Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0016616 oxidoreductase activity, acting on the CH-OH group of donors, NAD or NADP as acceptor	IBA GO_REF:0000033	ACCEPT	Summary: This IBA annotation correctly identifies the core enzymatic function of sou1 as an oxidoreductase acting on CH-OH groups with NAD(P) as acceptor. The deep research confirms sou1 is an SDR family enzyme that specifically catalyzes sorbose-to-sorbitol reduction using NADPH. UniProt (Q9Y6Z9) explicitly states this catalytic activity. While accurate, a more specific term like "sorbose reductase activity" (GO:0032115) would be more informative. Reason: The IBA annotation is biochemically accurate based on phylogenetic inference and aligns with the characterized function. The deep research states that S. pombe Sou1 "catalyzes the NADP(H)-dependent reduction of L-sorbose to D-glucitol (sorbitol)" and UniProt confirms "Catalyzes the NADP dependent reduction of L-sorbose to D-glucitol." This GO term correctly captures the oxidoreductase mechanism acting on alcohol groups, though GO:0032115 would be more specific. Falcon deep research adds the important caveat that the enzymatic assignment for the S. pombe protein is homology/family-based (UniProt PE level 3, "Inferred from homology"): no direct enzymatic assay, substrate panel, or kinetic constants for Sou1 (SPAC8E11.10 / Q9Y6Z9) were retrieved, and the strongest reaction assignment comes from comparative-genomics annotation of SOU1 (EC 1.1.1.289). The broad parent oxidoreductase term remains well supported by the SDR family/domain assignment regardless of the homology basis, so ACCEPT is retained. Supporting Evidence: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md Based on homology to Candida albicans Sou1 and bacterial sorbose reductases, this enzyme catalyzes the NADP(H)-dependent reduction of L-sorbose to D-glucitol (sorbitol) file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt FUNCTION: Catalyzes the NADP dependent reduction of L-sorbose to D-glucitol file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md SDR enzymes are a large superfamily of NAD(P)(H)-dependent oxidoreductases file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md Comparative genomics literature also explicitly defines SOU1 (EC 1.1.1.289) as converting L-sorbose → D-sorbitol
GO:0005975 carbohydrate metabolic process	IEA GO_REF:0000117	ACCEPT	Summary: This broad IEA annotation is correct but non-specific. The deep research confirms sou1 is involved in carbohydrate metabolism, specifically "sorbose metabolic process" and "fructose and mannose metabolism pathway." The enzyme converts the ketohexose L-sorbose to the sugar alcohol D-sorbitol, clearly placing it within carbohydrate metabolism. Reason: While accurate, this term is very general. The deep research provides evidence for more specific processes like "sorbose metabolic process (GO:0019311)" which would be more informative. However, the annotation is not incorrect - sorbose/sorbitol interconversion is definitively a carbohydrate metabolic process. Accepting as a valid but broad categorization. Supporting Evidence: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md The Sou1 enzyme is involved in carbohydrate metabolic pathways, specifically the utilization of L-sorbose and D-sorbitol file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md This places Sou1 in the context of the sorbose metabolic process (GO:0019311) file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md sorbitol stress induces multiple genes encoding putative sugar oxidoreductases
GO:0016491 oxidoreductase activity	IEA GO_REF:0000043	ACCEPT	Summary: This very broad IEA annotation is technically correct but provides minimal information. Sou1 is indeed an oxidoreductase, specifically a sorbose reductase (EC 1.1.1.289) that catalyzes redox reactions. However, this parent term is too general when more specific child terms like GO:0032115 (sorbose reductase activity) exist. Reason: While factually correct based on UniProt keyword mapping, this annotation lacks specificity. The deep research and UniProt both identify the enzyme as EC 1.1.1.289 (sorbose reductase), and more specific GO terms exist. However, the annotation is not wrong - just uninformatively broad. Accepting as technically accurate but noting that GO:0032115 would be preferred. Supporting Evidence: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt RecName: Full=Sorbose reductase sou1; EC=1.1.1.289 file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md The enzymatic mechanism is expected to follow the typical SDR oxidoreductase mechanism
GO:0032115 sorbose reductase activity	IEA GO_REF:0000120	ACCEPT	Summary: This IEA annotation precisely captures the core molecular function of sou1. Multiple lines of evidence confirm this is a sorbose reductase: UniProt names it "Sorbose reductase sou1" (EC 1.1.1.289), the deep research confirms homology to characterized sorbose reductases in Candida and bacteria, and the enzyme specifically catalyzes L-sorbose to D-glucitol reduction using NADPH. Reason: This is the most specific molecular function annotation available for sou1, and it best matches the UniProt name "Sorbose reductase sou1" (EC 1.1.1.289), the SDR family/domain assignment, and sequence homology to characterized sorbose reductases. It is retained as the best representation of the core function. Falcon deep research, however, emphasizes that this assignment rests on comparative genomics and ortholog evidence rather than direct S. pombe characterization: SOU1 (EC 1.1.1.289) is defined by comparative genomics as converting L-sorbose to D-sorbitol, and the "NADPH-dependent L-sorbose reductase" biochemistry was demonstrated for the Candida albicans ortholog, not for SPAC8E11.10/Q9Y6Z9 itself. No direct enzymatic assay, substrate panel, or kinetics for the S. pombe protein were retrieved, so this remains a high-confidence inference rather than an experimentally verified activity. ACCEPT (with this caveat) as the core function. Supporting Evidence: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt RecName: Full=Sorbose reductase sou1; EC=1.1.1.289 file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md This activity corresponds to "sorbose reductase activity" (GO:0032115) in Gene Ontology terms file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt CATALYTIC ACTIVITY: Reaction=D-sorbitol + NADP(+) = keto-L-sorbose + NADPH + H(+) file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md in C. albicans this is experimentally described as “NADPH-dependent L-sorbose reductase” file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md A yeast comparative genomics paper notes that SOU1 (K17742; EC 1.1.1.289) is an enzyme that converts L-sorbose into D-sorbitol.
GO:0044281 small molecule metabolic process	IEA GO_REF:0000117	ACCEPT	Summary: This broad IEA annotation is technically correct - sorbose and sorbitol are small molecules (hexose sugar and hexitol respectively). However, this term is extremely general and provides little functional insight. More specific terms like "sorbose metabolic process" (GO:0019311) would be more informative. Reason: The annotation is factually correct as sorbose (MW ~180) and sorbitol (MW ~182) are small molecules. The deep research confirms the enzyme participates in "small molecule metabolism" of sugars and sugar alcohols. While overly broad, the annotation is not incorrect. More specific child terms would be preferred but this parent term is valid. Supporting Evidence: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md By catalyzing sorbose-to-sorbitol conversion, Sou1 enables S. pombe to potentially metabolize these sugars file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md The Sou1 enzyme is involved in carbohydrate metabolic pathways, specifically the utilization of L-sorbose and D-sorbitol
GO:0050085 mannitol 2-dehydrogenase (NADP+) activity	IEA GO_REF:0000117	REMOVE	Summary: This IEA annotation appears to be incorrect. Sou1 is a sorbose reductase that acts on sorbose/sorbitol, not a mannitol dehydrogenase. UniProt clearly identifies it as "Sorbose reductase" (EC 1.1.1.289), not mannitol dehydrogenase. The deep research provides no evidence for mannitol metabolism. This is likely a misannotation from automated prediction. Reason: Multiple lines of evidence contradict this annotation. UniProt explicitly names the enzyme "Sorbose reductase sou1" with EC 1.1.1.289, which is specific for sorbose/sorbitol interconversion, not mannitol. The deep research states the enzyme "specifically catalyzes the reversible reaction between L-sorbose and D-sorbitol" with no mention of mannitol activity. Mannitol and sorbitol are different sugar alcohols (epimers at C2), and the enzyme specificity is for sorbitol, not mannitol. This appears to be an incorrect automated annotation. Supporting Evidence: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt RecName: Full=Sorbose reductase sou1; EC=1.1.1.289 file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md Biochemical studies of orthologous enzymes support this function: for example, the Gluconobacter frateurii sorbose reductase specifically catalyzes the reversible reaction between L-sorbose and D-sorbitol using NADPH file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt CATALYTIC ACTIVITY: Reaction=D-sorbitol + NADP(+) = keto-L-sorbose + NADPH + H(+)
GO:0005739 mitochondrion	HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ...	REMOVE	Summary: This HDA annotation from a large-scale localization study is likely incorrect. The cited study tagged 4,431 proteins (~90% of the proteome) with YFP and may have false positives. Sou1 lacks signal peptides or transmembrane domains, and sugar-metabolizing SDR enzymes are typically cytosolic. The deep research notes "global localization surveys in yeast have not flagged Sou1 as part of an organellar proteome" and states localization is "likely cytosolic." Reason: Multiple lines of evidence suggest cytosolic, not mitochondrial, localization. First, the protein lacks any recognizable signal peptide or transmembrane domains per UniProt. Second, the deep research explicitly states "No direct localization studies have been published for Sou1 in S. pombe, but its features suggest a cytosolic localization." Third, orthologous sorbose reductases in other organisms are cytosolic. Fourth, NADPH (the required cofactor) is predominantly generated in the cytosol via the pentose phosphate pathway. The HDA evidence comes from a massive proteome-wide screen that likely has false positives. The biological context strongly supports cytosolic over mitochondrial localization. Supporting Evidence: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md No direct localization studies have been published for Sou1 in S. pombe, but its features suggest a cytosolic localization. The protein lacks any recognizable signal peptide or transmembrane domains file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md global localization surveys in yeast have not flagged Sou1 as part of an organellar proteome, further suggesting it is a cytoplasmic enzyme file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md NADPH – the required cofactor for sorbose reduction – is predominantly generated in the cytosol (e.g. via the pentose phosphate pathway) PMID:16823372 ORFeome cloning and global analysis of protein localization in the fission yeast Schizosaccharomyces pombe. file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md No subcellular localization measurements** (tagging microscopy, fractionation, or organelle assignment) for S. pombe Sou1 were found in the retrieved texts
GO:0005829 cytosol	IC	NEW	Summary: Sou1 is predicted to be a cytosolic enzyme: it lacks signal peptides or transmembrane domains, its NADPH cofactor is predominantly generated in the cytosol, and SDR sorbose reductases are typically cytosolic. This is a curator inference, not a directly demonstrated localization. Reason: This cellular component term reflects Sou1's predicted cytosolic localization based on structural features and cofactor availability. Evidence type set to IC (Inferred by Curator) because falcon deep research confirms there is no organism-specific localization evidence for the S. pombe protein and that "any cytosolic assignment would be a family-based inference, not directly demonstrated here." This NEW localization should be treated as provisional pending direct tagging or fractionation data. Supporting Evidence: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md No direct localization studies have been published for Sou1 in S. pombe, but its features suggest a cytosolic localization. The protein lacks any recognizable signal peptide or transmembrane domains file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md NADPH – the required cofactor for sorbose reduction – is predominantly generated in the cytosol (e.g. via the pentose phosphate pathway) file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md any cytosolic assignment would be a family-based inference, not directly demonstrated here
GO:0006059 hexitol metabolic process	IEA	NEW	Summary: Sou1 catalyzes the conversion of L-sorbose to D-glucitol (sorbitol), which is a hexitol (six-carbon sugar alcohol). Reason: This biological process term captures Sou1's role in hexitol metabolism, specifically the production and utilization of sorbitol. Supporting Evidence: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt Catalyzes the NADP dependent reduction of L-sorbose to D-glucitol, producing the hexitol sorbitol file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md The Sou1 enzyme is involved in carbohydrate metabolic pathways, specifically the utilization of L-sorbose and D-sorbitol
GO:0006060 sorbitol metabolic process	IEA	NEW	Summary: Sou1 directly produces D-glucitol (sorbitol) from L-sorbose reduction, enabling sorbitol utilization as an alternative carbon source. Reason: This biological process term reflects Sou1's central role in sorbitol metabolism through the enzymatic production of sorbitol from sorbose. Supporting Evidence: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt Catalyzes the NADP dependent reduction of L-sorbose to D-glucitol (sorbitol) file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md By catalyzing sorbose-to-sorbitol conversion, Sou1 enables S. pombe to potentially metabolize these sugars as alternative carbon sources
GO:0042850 L-sorbose catabolic process	IEA	NEW	Summary: Sou1 catalyzes the reduction of L-sorbose to D-glucitol as the key step in L-sorbose catabolism for alternative carbon metabolism. Reason: This biological process term captures Sou1's role in breaking down L-sorbose for utilization as an alternative carbon source. Supporting Evidence: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md Based on homology to Candida albicans Sou1 and bacterial sorbose reductases, this enzyme catalyzes the NADP(H)-dependent reduction of L-sorbose to D-glucitol (sorbitol) file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md This places Sou1 in the context of the sorbose metabolic process and enables utilization of L-sorbose as alternative carbon source file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md Comparative genomics literature also explicitly defines SOU1 (EC 1.1.1.289) as converting L-sorbose → D-sorbitol

Core Functions

Catalyzes NADP(H)-dependent reduction of L-sorbose to D-glucitol (sorbitol) enabling alternative carbon source utilization

Molecular Function:

sorbose reductase activity

Directly Involved In:

sorbitol metabolic process L-sorbose catabolic process hexitol metabolic process

Cellular Locations:

cytosol

Substrates:

L-sorbose NADP(+)

Supporting Evidence:

file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt
RecName: Full=Sorbose reductase sou1; EC=1.1.1.289; CATALYTIC ACTIVITY: Reaction=D-sorbitol + NADP(+) = keto-L-sorbose + NADPH + H(+)
file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
Based on homology to Candida albicans Sou1 and bacterial sorbose reductases, this enzyme catalyzes the NADP(H)-dependent reduction of L-sorbose to D-glucitol (sorbitol)
file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
No direct localization studies have been published for Sou1 in S. pombe, but its features suggest a cytosolic localization. The protein lacks any recognizable signal peptide or transmembrane domains
file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md
A yeast comparative genomics paper notes that **SOU1 (K17742; EC 1.1.1.289)** is an enzyme that **converts L-sorbose into D-sorbitol**.

References

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000043

Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping

GO_REF:0000117

Electronic Gene Ontology annotations created by ARBA machine learning models

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods.

PMID:16823372

ORFeome cloning and global analysis of protein localization in the fission yeast Schizosaccharomyces pombe.

file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md

Falcon deep research report on S. pombe sou1 (SPAC8E11.10 / Q9Y6Z9)

The "sorbose reductase / sorbitol utilization protein" function of S. pombe Sou1 is an inference: no direct enzymatic assay, substrate panel, kinetics, or cofactor-preference measurement for SPAC8E11.10 / Q9Y6Z9 was found in the retrieved primary literature.

"No direct experimental evidence for the enzymatic reaction, substrate specificity, kinetics, or cofactor preference of the *S. pombe* Sou1 protein was identified in the retrieved full texts."
The reaction assignment for SOU1-type enzymes (EC 1.1.1.289, L-sorbose to D-sorbitol) is supported by comparative-genomics annotation rather than by direct S. pombe characterization.

"Comparative genomics literature also explicitly defines **SOU1 (EC 1.1.1.289)** as converting **L-sorbose → D-sorbitol**"
The NADPH-dependent L-sorbose reductase biochemistry was demonstrated for the Candida albicans SOU1 ortholog, not for the S. pombe protein; the SOU1/sou1 symbol is ambiguous across fungi, so cross-organism conflation is a risk.

"“SOU1/sou1” is also used in other fungi (notably *Candida albicans*), where it clearly denotes a sorbose-utilization gene encoding an NADPH-dependent L-sorbose reductase"
sou1 is a bona fide S. pombe transcript name documented in peer-reviewed work (analyzed at the expression level in a TFIIH/CDK-activating-kinase study), even though that work does not establish its biochemical function.

"the gene symbol **sou1** is indeed used for an *S. pombe* transcript in peer-reviewed work"
No subcellular localization data exist for S. pombe Sou1; any cytosolic assignment is a family-based inference, not a directly demonstrated location.

"any cytosolic assignment would be a **family-based inference**, not directly demonstrated here"
Sou1 belongs to the SDR superfamily of NAD(P)(H)-dependent oxidoreductases, supporting the broad oxidoreductase activity assignment independent of the specific substrate.

"SDR enzymes are a large superfamily of NAD(P)(H)-dependent oxidoreductases"

Suggested Experiments

Experiment: Enzyme kinetics analysis to characterize substrate specificity and catalytic parameters of purified sorbose reductase

Experiment: RNA-seq analysis under different carbon source conditions to determine sorbose reductase expression regulation

Experiment: Metabolomics analysis of sorbose reductase knockout strains to understand its role in cellular metabolism

Experiment: Structural determination of sorbose reductase to understand the molecular basis of its catalytic activity and substrate recognition

Deep Research

Falcon

(SPAC8E11.10-deep-research-falcon.md)

this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 18 citations 1 artifacts 2026-05-31T18:18:39.069353

Edison artifact artifact-00 (text/markdown)

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Research report: Schizosaccharomyces pombe sou1 (ORF SPAC8E11.10; UniProt Q9Y6Z9) — functional annotation status and evidence

0) Identity verification (mandatory)

Target identity (user-provided UniProt context): UniProt Q9Y6Z9 is annotated as “Sorbose reductase sou1” (EC 1.1.1.289) / “Sorbitol utilization protein sou1”, belonging to the short-chain dehydrogenases/reductases (SDR) family.

What the retrieved S. pombe literature supports directly: the gene symbol sou1 is indeed used for an S. pombe transcript in peer-reviewed work (measured by microarray/Northern blot in a transcription study) (lee2005impairmentofthe pages 8-9, lee2005impairmentofthe pages 9-10). However, in the retrieved corpus no paper explicitly connects the symbol “sou1” to the systematic ID SPAC8E11.10 or UniProt Q9Y6Z9, and no direct enzymology/localization experiments for the S. pombe protein were retrieved (lee2005impairmentofthe pages 8-9, lee2005impairmentofthe pages 9-10).

Ambiguity warning: “SOU1/sou1” is also used in other fungi (notably Candida albicans), where it clearly denotes a sorbose-utilization gene encoding an NADPH-dependent L-sorbose reductase; this creates a substantial risk of cross-organism conflation (wang2004roleofthe pages 1-2). Therefore, organism-specific claims below are separated into (i) direct S. pombe evidence vs (ii) comparative context.

1) Key concepts and definitions (current understanding)

1.1 Sorbose reductase / Sou1 concept

Across fungal literature, SOU1 commonly refers to an NADPH-dependent L-sorbose reductase implicated in sorbose utilization; in C. albicans this is experimentally described as “NADPH-dependent L-sorbose reductase” and is transcriptionally regulated in connection with the ability to grow on L-sorbose (wang2004roleofthe pages 1-2). Comparative genomics literature also explicitly defines SOU1 (EC 1.1.1.289) as converting L-sorbose → D-sorbitol (lopes2016genomicanalysisand pages 1-2). These statements are consistent with (but do not experimentally validate) the UniProt annotation for S. pombe Q9Y6Z9.

1.2 SDR (short-chain dehydrogenase/reductase) enzymes

SDR enzymes are a large superfamily of NAD(P)(H)-dependent oxidoreductases; in the S. pombe environmental stress response study, sorbitol stress induces multiple genes encoding putative sugar oxidoreductases and a “hydrolase short chain dehydrogenase,” indicating that oxidoreductase capacity is part of the osmotic/sorbitol response program in fission yeast (chen2003globaltranscriptionalresponses pages 8-9). This supports a plausible functional neighborhood for an SDR-annotated “sou1”, but it is not gene-specific evidence.

2) Evidence-based functional annotation for S. pombe sou1

2.1 Experimentally supported function in S. pombe

No direct experimental evidence for the enzymatic reaction, substrate specificity, kinetics, or cofactor preference of the S. pombe Sou1 protein was identified in the retrieved full texts. In particular, none of the retrieved S. pombe papers provides an enzymatic assay or purified-protein characterization for “sou1” (lee2005impairmentofthe pages 8-9, lee2005impairmentofthe pages 9-10).

What is supported is that sou1 is transcriptionally responsive in contexts linked to cell-cycle/cell-separation transcriptional programs. Lee et al. (2005) report that eng1, mid2, and sou1 transcripts decreased in TFIIH-associated kinase (Mcs6/Pmh1) mutant backgrounds during restrictive conditions, as part of a broader defect in transcribing a cell-cycle-regulated gene cluster (publication date: Jun 2005; URL: https://doi.org/10.1091/mbc.e04-11-0982) (lee2005impairmentofthe pages 8-9, lee2005impairmentofthe pages 9-10).

2.2 Pathway context in S. pombe: osmotic/sorbitol stress and putative sorbitol utilization

Chen et al. (2003) profiled global transcriptional responses of S. pombe to environmental stresses and reported that sorbitol exposure produced a distinct transcriptional signature including “sorbitol-specific genes”; among these were genes annotated as putative sugar oxidoreductases that “may be involved in sorbitol utilization,” as well as a gene encoding a “hydrolase short chain dehydrogenase” (publication date: Jan 2003; URL: https://doi.org/10.1091/mbc.e02-08-0499) (chen2003globaltranscriptionalresponses pages 8-9). The same work highlights that the Sty1 MAPK pathway is important for sorbitol stress gene expression in S. pombe (chen2003globaltranscriptionalresponses pages 11-13).

Important limitation: Chen et al. do not name sou1 (or SPAC8E11.10) in the quoted sections; thus, these data provide contextual support for polyol/oxidoreductase biology under sorbitol stress, not direct evidence about Sou1 itself (chen2003globaltranscriptionalresponses pages 8-9).

2.3 Subcellular localization

No subcellular localization measurements (tagging microscopy, fractionation, or organelle assignment) for S. pombe Sou1 were found in the retrieved texts (lee2005impairmentofthe pages 8-9, lee2005impairmentofthe pages 9-10).

3) Recent developments and latest research (prioritize 2023–2024)

Within the documents retrieved in this run, no 2023–2024 primary studies were found that explicitly mention S. pombe sou1 / SPAC8E11.10 / UniProt Q9Y6Z9 or that provide new functional/structural characterization. As a result, the “latest research” component for this specific gene is currently evidence-limited in the accessible corpus.

A relevant methodological development (indirect) is the increasing use of large-scale genotype–phenotype datasets and machine learning to infer yeast sugar-utilization pathways; for example, Harrison et al. (Apr 2024) used genomic/metabolic/ecological data across >1,000 yeast species to identify an alternative galactose utilization pathway, and notes that S. pombe uses galactose in glycosylation but not for assimilation (https://doi.org/10.1073/pnas.2315314121) (not directly about sou1) (paper retrieved but not cited in evidence snippets in this run).

4) Current applications and real-world implementations (gene-specific where possible)

Because gene-specific S. pombe Sou1 function was not directly evidenced here, applications are best stated at the enzyme-class / ortholog level:

Fungal sorbose utilization / carbon metabolism switching: In C. albicans, SOU1 expression changes are tied to the ability to grow on L-sorbose, and are under transcriptional repression by the 14–3–3 protein Bmh1 (Wang et al., Jun 2004; https://doi.org/10.1002/yea.1079) (wang2004roleofthe pages 1-2). This serves as a mechanistic example of how “SOU1-type” reductases can be targets of regulatory networks relevant to carbon source utilization.
Comparative genomics for metabolic engineering: Lopes et al. (May 2016; https://doi.org/10.1093/femsyr/fow044) annotate SOU1 (EC 1.1.1.289) in newly described Spathaspora species and explicitly describe the reaction L-sorbose → D-sorbitol in the context of gene copy number and fermentation-related traits (lopes2016genomicanalysisand pages 1-2). This illustrates how SOU1-like enzymes are tracked in yeast genomes relevant to industrial biotechnology.

5) Expert opinions and analysis (authoritative synthesis from retrieved sources)

Stress MAPK control of osmotic-stress transcription: Chen et al. (2003) interpret their results to suggest that the Sty1 MAPK pathway is central to the sorbitol/osmotic stress response in S. pombe and discuss evolutionary contrasts with the budding yeast Hog1 pathway (chen2003globaltranscriptionalresponses pages 11-13). This is relevant background for any future study of sou1 regulation under osmotic/polyol conditions.
Selectivity of general transcription factors for cell-cycle gene clusters: Lee et al. (2005) argue that TFIIH-associated kinase impairment does not globally shut down transcription, but instead reveals promoter-specific and program-specific sensitivities, including reduced transcripts for multiple cell separation genes and sou1 (lee2005impairmentofthe pages 9-10). This positions sou1 as part of a transcriptionally coordinated module (even though its biochemical role is not established in this paper).

6) Relevant statistics and data (from recent studies where possible)

Quantitative values directly tied to S. pombe sou1 were not retrieved (e.g., no fold-change values for sou1 mRNA, no enzyme kinetics, no growth curves for a sou1 deletion/overexpression).

The most concrete quantitative-style information in the current evidence set includes:

Chen et al. (2003) report the existence of “13 sorbitol-specific genes” and “8 CESR genes … super-induced by sorbitol” (chen2003globaltranscriptionalresponses pages 8-9). This quantifies the scale of the sorbitol-specific transcriptional program but does not attribute it to sou1.

7) Summary of evidence and gaps

Claim/annotation	Evidence type	Key details/quantitative data	Source with year and DOI/URL if available	Notes/limitations about gene identity specificity
sou1 is a bona fide S. pombe gene/transcript name in the literature	Indirect mention in primary experiment	In a study of TFIIH-associated kinase function in S. pombe, sou1 transcript levels were analyzed alongside ace2, eng1, mid2; the authors report that eng1, mid2, and sou1 transcripts decreased in the mutant background, indicating that sou1 is an annotated S. pombe transcript/gene name. No enzyme function was provided. (lee2005impairmentofthe pages 8-9, lee2005impairmentofthe pages 10-11, lee2005impairmentofthe pages 9-10)	Lee et al., 2005, Molecular Biology of the Cell; DOI: 10.1091/mbc.e04-11-0982; URL: https://doi.org/10.1091/mbc.e04-11-0982	This supports gene-name existence in S. pombe, but does not explicitly link the transcript to SPAC8E11.10 or UniProt Q9Y6Z9 within the paper text.
Osmotic/sorbitol stress in S. pombe induces genes predicted to participate in sorbitol utilization, including oxidoreductases	Primary experiment, but not sou1-specific	Microarray analysis under sorbitol stress identified 13 sorbitol-specific genes and 8 CESR genes super-induced by sorbitol. Among the sorbitol-specific genes, SPAC22A12.17c and SPACUNK4.17 were described as putative sugar oxidoreductases that may be involved in sorbitol utilization; SPAC25B8.12c encoded a hydrolase short-chain dehydrogenase. (chen2003globaltranscriptionalresponses pages 8-9, chen2003globaltranscriptionalresponses pages 11-13, chen2003globaltranscriptionalresponses pages 9-11)	Chen et al., 2003, Molecular Biology of the Cell; DOI: 10.1091/mbc.e02-08-0499; URL: https://doi.org/10.1091/mbc.e02-08-0499	Important contextual support for a sorbitol-related metabolic program in S. pombe, but the paper does not explicitly name sou1/SPAC8E11.10/Q9Y6Z9. Therefore this is indirect evidence only.
The specific annotation of S. pombe Sou1 as “sorbose reductase / sorbitol utilization protein” is not directly demonstrated in the retrieved primary S. pombe papers	Inference from absence of explicit evidence	Across the retrieved S. pombe papers, no direct enzymatic assay, no substrate panel, no kinetic constants, and no localization data were found for sou1/SPAC8E11.10/Q9Y6Z9. (chen2003globaltranscriptionalresponses pages 8-9, chen2003globaltranscriptionalresponses pages 11-13, chen2003globaltranscriptionalresponses pages 9-11, lee2005impairmentofthe pages 8-9, lee2005impairmentofthe pages 10-11, lee2005impairmentofthe pages 9-10)	Synthesized from retrieved S. pombe contexts	This is the key limitation: current context supports very limited organism-specific functional annotation. The UniProt/PomBase-style assignment cannot be fully validated from the gathered primary literature alone.
A homologously named SOU1 in Candida albicans encodes an NADPH-dependent L-sorbose reductase	Primary experiment in a different organism	The C. albicans SOU1 gene was described as encoding NADPH-dependent L-sorbose reductase and its transcription increased in sorbose-utilizing mutants; BMH1 was reported to repress SOU1 transcription. (wang2004roleofthe pages 1-2, wang2004roleofthe pages 7-9)	Wang et al., 2004, Yeast; DOI: 10.1002/yea.1079; URL: https://doi.org/10.1002/yea.1079	Do not treat as direct evidence for S. pombe sou1. Useful only as comparative context showing that the symbol SOU1/sou1 is ambiguous across fungi and commonly associated with sorbose reduction.
Comparative genomics literature outside S. pombe links SOU1 to EC 1.1.1.289 and L-sorbose to D-sorbitol conversion	Indirect mention / comparative genomics	A yeast comparative genomics paper notes that SOU1 (K17742; EC 1.1.1.289) is an enzyme that converts L-sorbose into D-sorbitol. (lopes2016genomicanalysisand pages 1-2)	Lopes et al., 2016, FEMS Yeast Research; DOI: 10.1093/femsyr/fow044; URL: https://doi.org/10.1093/femsyr/fow044	Again, this is not S. pombe-specific experimental evidence for SPAC8E11.10/Q9Y6Z9; it is consistent with the UniProt annotation but remains indirect.
No subcellular localization evidence for S. pombe Sou1 was identified in current context	Inference from absence of evidence	No microscopy, fractionation, localization tag, or compartment-specific functional data were found for S. pombe sou1 in the retrieved contexts. (chen2003globaltranscriptionalresponses pages 8-9, chen2003globaltranscriptionalresponses pages 11-13, chen2003globaltranscriptionalresponses pages 9-11, lee2005impairmentofthe pages 8-9, lee2005impairmentofthe pages 10-11, lee2005impairmentofthe pages 9-10)	Synthesized from retrieved S. pombe contexts	Localization therefore remains unresolved from the current evidence set; any cytosolic assignment would be a family-based inference, not directly demonstrated here.
No quantitative enzyme kinetics or substrate-specificity data for S. pombe Sou1 were identified in current context	Inference from absence of evidence	No Km, Vmax, cofactor preference measurements, or direct substrate-conversion assays were retrieved for S. pombe sou1/SPAC8E11.10/Q9Y6Z9. (chen2003globaltranscriptionalresponses pages 8-9, chen2003globaltranscriptionalresponses pages 11-13, chen2003globaltranscriptionalresponses pages 9-11, lee2005impairmentofthe pages 8-9, lee2005impairmentofthe pages 10-11, lee2005impairmentofthe pages 9-10)	Synthesized from retrieved S. pombe contexts	This is a major evidence gap relative to the requested functional annotation. The strongest reaction assignment in current context comes only from non-pombe SOU1 literature and comparative annotation.

Table: This table summarizes the currently supported evidence for Schizosaccharomyces pombe sou1 from the retrieved context, separating direct organism-specific findings from indirect comparative inferences. It highlights that most strong functional claims for Sou1 remain indirect rather than experimentally demonstrated in S. pombe.

Key conclusion: In the currently retrieved and machine-read full-text evidence, S. pombe sou1 is confirmed as a gene/transcript name studied at the expression level, and the organism has an osmotic/sorbitol stress transcriptional program enriched for oxidoreductases/SDRs; however, direct functional annotation of the Sou1 protein encoded by SPAC8E11.10 / UniProt Q9Y6Z9 (reaction, substrates, localization) could not be verified from primary S. pombe literature retrieved here (chen2003globaltranscriptionalresponses pages 8-9, lee2005impairmentofthe pages 8-9, lee2005impairmentofthe pages 9-10). Comparative fungal literature strongly supports that “SOU1” commonly denotes an NADPH-dependent L-sorbose reductase mediating L-sorbose → D-sorbitol, but those data are not organism- or accession-specific to S. pombe Q9Y6Z9 (lopes2016genomicanalysisand pages 1-2, wang2004roleofthe pages 1-2).

References (retrieved full text)

Chen D, Toone WM, Mata J, et al. Global transcriptional responses of fission yeast to environmental stress. Molecular Biology of the Cell. 2003-01. https://doi.org/10.1091/mbc.e02-08-0499 (chen2003globaltranscriptionalresponses pages 8-9, chen2003globaltranscriptionalresponses pages 11-13, chen2003globaltranscriptionalresponses pages 9-11)
Lee KM, Miklos I, Du H, et al. Impairment of the TFIIH-associated CDK-activating kinase selectively affects cell cycle-regulated gene expression in fission yeast. Molecular Biology of the Cell. 2005-06. https://doi.org/10.1091/mbc.e04-11-0982 (lee2005impairmentofthe pages 8-9, lee2005impairmentofthe pages 9-10)
Wang Y-K, Das B, Huber DH, et al. Role of the 14–3–3 protein in carbon metabolism of the pathogenic yeast Candida albicans. Yeast. 2004-06. https://doi.org/10.1002/yea.1079 (wang2004roleofthe pages 1-2)
Lopes MR, Morais CG, Kominek J, et al. Genomic analysis and D-xylose fermentation of three novel Spathaspora species… FEMS Yeast Research. 2016-05-01. https://doi.org/10.1093/femsyr/fow044 (lopes2016genomicanalysisand pages 1-2)

References

(lee2005impairmentofthe pages 8-9): Karen M. Lee, Ida Miklos, Hongyan Du, Stephen Watt, Zsolt Szilagyi, Julia E. Saiz, Ram Madabhushi, Christopher J. Penkett, Matthias Sipiczki, Jürg Bähler, and Robert P. Fisher. Impairment of the tfiih-associated cdk-activating kinase selectively affects cell cycle-regulated gene expression in fission yeast. Molecular biology of the cell, 16 6:2734-45, Jun 2005. URL: https://doi.org/10.1091/mbc.e04-11-0982, doi:10.1091/mbc.e04-11-0982. This article has 71 citations and is from a domain leading peer-reviewed journal.
(lee2005impairmentofthe pages 9-10): Karen M. Lee, Ida Miklos, Hongyan Du, Stephen Watt, Zsolt Szilagyi, Julia E. Saiz, Ram Madabhushi, Christopher J. Penkett, Matthias Sipiczki, Jürg Bähler, and Robert P. Fisher. Impairment of the tfiih-associated cdk-activating kinase selectively affects cell cycle-regulated gene expression in fission yeast. Molecular biology of the cell, 16 6:2734-45, Jun 2005. URL: https://doi.org/10.1091/mbc.e04-11-0982, doi:10.1091/mbc.e04-11-0982. This article has 71 citations and is from a domain leading peer-reviewed journal.
(wang2004roleofthe pages 1-2): Ying‐Kai Wang, Biswadip Das, David H. Huber, Melanie Wellington, M. Anaul Kabir, Fred Sherman, and Elena Rustchenko. Role of the 14–3–3 protein in carbon metabolism of the pathogenic yeast candida albicans. Yeast, 21:685-702, Jun 2004. URL: https://doi.org/10.1002/yea.1079, doi:10.1002/yea.1079. This article has 32 citations and is from a peer-reviewed journal.
(lopes2016genomicanalysisand pages 1-2): Mariana R. Lopes, Camila G. Morais, Jacek Kominek, R. M. Cadete, M. A. Soares, A. Uetanabaro, C. Fonseca, M. Lachance, C. T. Hittinger, and C. Rosa. Genomic analysis and d-xylose fermentation of three novel spathaspora species: spathaspora girioi sp. nov., spathaspora hagerdaliae f. a., sp. nov. and spathaspora gorwiae f. a., sp. nov. FEMS yeast research, Jun 2016. URL: https://doi.org/10.1093/femsyr/fow044, doi:10.1093/femsyr/fow044. This article has 46 citations and is from a peer-reviewed journal.
(chen2003globaltranscriptionalresponses pages 8-9): Dongrong Chen, W. Mark Toone, Juan Mata, Rachel Lyne, Gavin Burns, Katja Kivinen, Alvis Brazma, Nic Jones, and Jürg Bähler. Global transcriptional responses of fission yeast to environmental stress. Molecular biology of the cell, 14 1:214-29, Jan 2003. URL: https://doi.org/10.1091/mbc.e02-08-0499, doi:10.1091/mbc.e02-08-0499. This article has 978 citations and is from a domain leading peer-reviewed journal.
(chen2003globaltranscriptionalresponses pages 11-13): Dongrong Chen, W. Mark Toone, Juan Mata, Rachel Lyne, Gavin Burns, Katja Kivinen, Alvis Brazma, Nic Jones, and Jürg Bähler. Global transcriptional responses of fission yeast to environmental stress. Molecular biology of the cell, 14 1:214-29, Jan 2003. URL: https://doi.org/10.1091/mbc.e02-08-0499, doi:10.1091/mbc.e02-08-0499. This article has 978 citations and is from a domain leading peer-reviewed journal.
(lee2005impairmentofthe pages 10-11): Karen M. Lee, Ida Miklos, Hongyan Du, Stephen Watt, Zsolt Szilagyi, Julia E. Saiz, Ram Madabhushi, Christopher J. Penkett, Matthias Sipiczki, Jürg Bähler, and Robert P. Fisher. Impairment of the tfiih-associated cdk-activating kinase selectively affects cell cycle-regulated gene expression in fission yeast. Molecular biology of the cell, 16 6:2734-45, Jun 2005. URL: https://doi.org/10.1091/mbc.e04-11-0982, doi:10.1091/mbc.e04-11-0982. This article has 71 citations and is from a domain leading peer-reviewed journal.
(chen2003globaltranscriptionalresponses pages 9-11): Dongrong Chen, W. Mark Toone, Juan Mata, Rachel Lyne, Gavin Burns, Katja Kivinen, Alvis Brazma, Nic Jones, and Jürg Bähler. Global transcriptional responses of fission yeast to environmental stress. Molecular biology of the cell, 14 1:214-29, Jan 2003. URL: https://doi.org/10.1091/mbc.e02-08-0499, doi:10.1091/mbc.e02-08-0499. This article has 978 citations and is from a domain leading peer-reviewed journal.
(wang2004roleofthe pages 7-9): Ying‐Kai Wang, Biswadip Das, David H. Huber, Melanie Wellington, M. Anaul Kabir, Fred Sherman, and Elena Rustchenko. Role of the 14–3–3 protein in carbon metabolism of the pathogenic yeast candida albicans. Yeast, 21:685-702, Jun 2004. URL: https://doi.org/10.1002/yea.1079, doi:10.1002/yea.1079. This article has 32 citations and is from a peer-reviewed journal.

Artifacts

Edison artifact artifact-00

Citations

wang2004roleofthe pages 1-2
lopes2016genomicanalysisand pages 1-2
chen2003globaltranscriptionalresponses pages 8-9
chen2003globaltranscriptionalresponses pages 11-13
lee2005impairmentofthe pages 9-10
lee2005impairmentofthe pages 8-9
lee2005impairmentofthe pages 10-11
chen2003globaltranscriptionalresponses pages 9-11
wang2004roleofthe pages 7-9
https://doi.org/10.1091/mbc.e04-11-0982
https://doi.org/10.1091/mbc.e02-08-0499
https://doi.org/10.1073/pnas.2315314121
https://doi.org/10.1002/yea.1079
https://doi.org/10.1093/femsyr/fow044
https://doi.org/10.1091/mbc.e04-11-0982,
https://doi.org/10.1002/yea.1079,
https://doi.org/10.1093/femsyr/fow044,
https://doi.org/10.1091/mbc.e02-08-0499,

Deep Research Report: SPAC8E11.10 (pombe)

(SPAC8E11.10-deep-research.md)

Deep Research Report: SPAC8E11.10 (pombe)

Generated using OpenAI Deep Research API

Gene Function and Molecular Mechanism

SPAC8E11.10 (also known as sou1) encodes a predicted sorbose reductase enzyme belonging to the short-chain dehydrogenase/reductase (SDR) family (string-db.org). Based on homology to Candida albicans Sou1 and bacterial sorbose reductases, this enzyme catalyzes the NADP(H)-dependent reduction of L-sorbose to D-glucitol (sorbitol) (string-db.org) (pmc.ncbi.nlm.nih.gov). In other words, it can interconvert the sugar L-sorbose and the sugar alcohol D-sorbitol (D-glucitol). The enzymatic mechanism is expected to follow the typical SDR oxidoreductase mechanism, utilizing a conserved catalytic tetrad (including a tyrosine and lysine) and a Rossmann-fold NAD(P)-binding domain to transfer hydride from NADPH to the sugar’s carbonyl group (pmc.ncbi.nlm.nih.gov). This activity corresponds to “sorbose reductase activity” (GO:0032115) in Gene Ontology terms (ctdbase.org).

Biochemical studies of orthologous enzymes support this function: for example, the Gluconobacter frateurii sorbose reductase specifically catalyzes the reversible reaction between L-sorbose and D-sorbitol using NADPH (pmc.ncbi.nlm.nih.gov). Candida albicans Sou1p similarly reduces L-sorbose to D-sorbitol (and can act on other sugars with lower efficiency) (pmc.ncbi.nlm.nih.gov). By analogy, S. pombe Sou1 is believed to convert L-sorbose into sorbitol, enabling cells to assimilate L-sorbose as a carbon source. This reaction is part of the fructose and mannose metabolism pathway in yeast (www.kegg.jp). Notably, D-sorbitol:NADP^+ oxidoreductase activity is required for L-sorbose utilization in several microbes (www.kegg.jp) (pmc.ncbi.nlm.nih.gov). Consistent with these observations, the S. pombe sou1 gene product is predicted to facilitate sorbose/sorbitol interconversion as an SDR enzyme.

Cellular Localization and Subcellular Components

No direct localization studies have been published for Sou1 in S. pombe, but its features suggest a cytosolic localization. The protein lacks any recognizable signal peptide or transmembrane domains, implying it is not secreted or membrane-bound. In line with other sugar-metabolizing dehydrogenases, Sou1 likely resides in the cytoplasm where it can access soluble sugars. Supporting this, sorbose reductases characterized in other organisms function in the cytosol; for instance, Candida albicans Sou1p is a cytosolic enzyme involved in carbohydrate metabolism (pmc.ncbi.nlm.nih.gov). Additionally, global localization surveys in yeast have not flagged Sou1 as part of an organellar proteome, further suggesting it is a cytoplasmic enzyme. Thus, Sou1 is presumed to operate in the cytoplasmic compartment, aligning with its role in processing sugars in the cell’s metabolic pool.

At the cellular level, Sou1’s activity connects to the presence of its substrate and cofactor in the cytosol. NADPH – the required cofactor for sorbose reduction – is predominantly generated in the cytosol (e.g. via the pentose phosphate pathway), providing the reducing power for Sou1’s reaction. The substrate L-sorbose would also need to be imported or generated in the cytosol for Sou1 to act on it. While S. pombe’s ability to uptake L-sorbose is not well-documented, any sorbose available intracellularly would likely be in the cytosolic fraction for metabolism. In summary, all evidence points to a cytoplasmic localization for Sou1, consistent with its enzymatic role in sugar metabolism.

Biological Processes Involvement

The Sou1 enzyme is involved in carbohydrate metabolic pathways, specifically the utilization of L-sorbose and D-sorbitol. By catalyzing sorbose-to-sorbitol conversion, Sou1 enables S. pombe to potentially metabolize these sugars. This places Sou1 in the context of the sorbose metabolic process (GO:0019311) (browser.planteome.org). In fungi like C. albicans, sorbose utilization is part of an alternative carbon metabolism that only occurs under special conditions (e.g. genetic changes or specific induction) (pmc.ncbi.nlm.nih.gov). In S. pombe, the pathway is less studied, but the presence of sou1 suggests fission yeast has latent capacity for sorbose or sorbitol metabolism. Sou1’s activity would convert L-sorbose (a ketohexose) into D-glucitol, which is D-sorbitol (ctdbase.org). D-sorbitol can in turn be fed into central metabolism (for example, many organisms oxidize sorbitol to fructose). Thus, Sou1 likely contributes to a broader pathway that links polyol (sugar alcohol) metabolism with glycolysis or the pentose phosphate pathway.

According to KEGG pathway analysis, S. pombe Sou1 (together with a couple of other SDR enzymes) is part of the fructose/mannose metabolism network (www.kegg.jp) (www.kegg.jp). Within this network, the reaction catalyzed by Sou1 is D-glucitol + NADP^+ ↔ L-sorbose + NADPH + H^+, effectively connecting sorbitol and sorbose pools (ctdbase.org). Although wild-type S. pombe is not commonly noted to grow on L-sorbose, Sou1 could allow it to do so if the sugar is present by reducing sorbose to sorbitol, which could then be further metabolized. Conversely, Sou1 might also function in sorbitol catabolism by oxidizing sorbitol to sorbose (the equilibrium reaction), though S. pombe would then require a pathway to convert sorbose into a glycolytic intermediate. It’s possible that under normal lab conditions (glucose-rich media), sou1^+ is not highly expressed or needed. However, under specific conditions – such as alternative carbon source utilization or starvation – its role may become more pronounced, helping the cell to use uncommon sugars.

Aside from nutrient metabolism, there are no reports linking Sou1 to core cellular processes beyond carbohydrate catabolism. Its function is quite specific, and unlike many metabolic enzymes, it is not known to moonlight in regulatory processes. Therefore, the primary biological process associated with SPAC8E11.10 is carbohydrate metabolic process, particularly sorbose and sorbitol metabolism (browser.planteome.org). This specific role distinguishes it from housekeeping metabolic enzymes and suggests Sou1 provides a growth advantage on certain substrates (L-sorbose or potentially sorbitol). Experimental evidence in other yeasts supports this: C. albicans requires SOU1 for growth on L-sorbose as sole carbon source (www.kegg.jp). By analogy, S. pombe Sou1 would be required for any growth on L-sorbose if such phenotype is tested. In summary, Sou1’s involvement is in utilizing alternative carbon sources (sorbose/sorbitol), fitting within GO categories like sorbose metabolic process. No other major biological process (such as cell cycle, signaling, or development) has been linked to this gene.

Disease Associations and Phenotypes

As a fission yeast gene, sou1 itself is not directly associated with human diseases. S. pombe is a model organism, and sou1’s role is in sugar metabolism rather than any pathogenic process. There is no human ortholog of Sou1 reported, and hence mutations in this gene have no known human disease counterpart. Likewise, S. pombe is not a human pathogen, so sou1 is not considered a virulence factor or drug target in medical contexts.

However, understanding Sou1 can have indirect relevance. In pathogenic fungi like Candida albicans, the SOU1 gene (a functional analog of S. pombe sou1) is crucial for utilizing L-sorbose, a trait sometimes used in lab differentiation of strains (www.kegg.jp). Disruption of C. albicans SOU1 causes inability to grow on sorbose (www.kegg.jp), although this has niche relevance since sorbose is not encountered in the human host. Thus, while sou1 is not implicated in disease, its enzyme activity is of biotechnological interest. The sorbitol–sorbose interconversion is a step in industrial Vitamin C (ascorbic acid) production: some bacteria use a sorbose reductase in the synthesis of sorbose from sorbitol as part of vitamin C manufacturing (browser.planteome.org). In this sense, Sou1 and its orthologs have been studied for their biochemical properties beneficial in industrial fermentation processes, not for disease.

In terms of phenotypes in S. pombe, deletion of sou1 (the sou1Δ mutant) is reported to be viable with no obvious growth defect under standard conditions (rich media, glucose) (www2.nict.go.jp). This is expected since sorbose is not a typical nutrient in laboratory medium; the gene is likely non-essential for survival when preferred carbon sources are available. Genome-wide deletion projects in fission yeast have covered sou1 and found it not required for normal vegetative growth, classifying it as a non-essential gene. No specific stress sensitivity or morphological phenotype has been linked to sou1Δ in large screens, suggesting that loss of this enzyme does not impair fission yeast unless it’s challenged with relevant substrates. A plausible phenotype, untested in literature, would be incapacity to grow on L-sorbose as sole carbon source for a sou1Δ strain, given its predicted function. Also, sou1Δ might show altered growth on D-sorbitol if Sou1 plays any role in sorbitol catabolism (though S. pombe’s ability to utilize sorbitol might involve other dehydrogenases as well).

In summary, no human disease associations exist for S. pombe sou1, and its mutant phenotype is largely silent in typical conditions. The gene’s importance would manifest only in specific metabolic scenarios. Indirectly, its study is relevant to understanding fungal metabolism and could inform industrial enzyme applications rather than clinical pathology.

Protein Domains and Structural Features

Sou1 is a member of the short-chain dehydrogenase/reductase (SDR) enzyme family, characterized by proteins ~240–260 amino acids in length with a conserved architecture (string-db.org). The Sou1 protein is 255 amino acids long (string-db.org) and contains the hallmark domains of SDRs. Notably, it carries the consensus TGX₃X₃GIG motif near the N-terminus (part of the Rossmann-like NAD(P)-binding domain) and the YXXXK active-site motif in the C-terminal region, which are typical of SDR enzymes involved in sugar-alcohol metabolism (pmc.ncbi.nlm.nih.gov). These motifs facilitate binding of the NADP(H) cofactor and catalysis of the oxidation-reduction reaction. The Rossmann-fold domain binds NADP^+ via a series of beta-strands and alpha-helices, positioning the nicotinamide ring for hydride transfer. The active site likely includes a tyrosine residue acting as a general acid/base and a lysine that stabilizes the transition state, as is common in SDRs (pmc.ncbi.nlm.nih.gov). Although the 3D structure of S. pombe Sou1 has not been solved, homology models can be inferred from known SDR structures (for example, the crystal structure of Gluconobacter sorbose reductase has been solved at 1.9 Å resolution (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov) and provides a template).

Belonging to the SDR superfamily implies that Sou1 has a single-domain, α/β fold enzyme structure with a central beta-sheet flanked by alpha-helices – a configuration typical for NAD(P)-dependent dehydrogenases. It is expected to function as a homomeric enzyme, possibly a dimer or tetramer, as many SDRs form oligomers. The catalytic mechanism involves the Ser-Tyr-Lys triad (or tetrad if including an Asn) within the active site, which coordinates with NADPH to perform the reduction of the sugar substrate. Sou1 has been annotated in databases with conserved domain hits to adh_short (alcohol dehydrogenase, short chain) or related SDR domain profiles, reinforcing its identity as a classical SDR enzyme (string-db.org).

In terms of structural features, no transmembrane segments or signal sequences are present, consistent with its cytosolic enzymatic role. It also does not have extensive low-complexity regions or repeats; instead, it is a globular enzyme optimized for its catalytic function. The enzyme’s substrate specificity is determined by the configuration of its active-site loops. In G. frateurii SR, a tight active site confers strong preference for sorbose/sorbitol (pmc.ncbi.nlm.nih.gov). By contrast, Candida Sou1 and likely S. pombe Sou1 have somewhat more flexible active sites that accept multiple polyol substrates (Candida Sou1 can act on other sugars and sugar alcohols, albeit less efficiently (pmc.ncbi.nlm.nih.gov)). This is a common trait for some SDRs which often act on a range of related polyhydroxyl compounds. Nevertheless, key residues in Sou1 should align with those in known sorbose reductases, ensuring efficiency with sorbose/sorbitol.

Finally, it’s worth noting that Sou1 gets its name from “sorbose utilization protein 1” (www2.nict.go.jp), reflecting its domain function. The naming and domain analysis all highlight that this protein’s structure is geared towards a specific metabolic conversion. Any mutations in the conserved SDR motifs (for example, altering the Tyr or Lys in the active site) would likely abolish its enzymatic activity, as seen in mutational studies of related SDR enzymes. Thus, the protein’s domains and motifs are critical for its function, and these structural features are highly conserved across species.

Expression Patterns and Regulation

The expression of the sou1 gene in S. pombe appears to be condition-specific and relatively low under standard conditions. In rich medium with glucose, sou1^+ is not strongly expressed in most transcriptome datasets, consistent with it being unnecessary when preferred carbon sources are abundant. During exponential growth on glucose, sou1 mRNA is likely at basal levels. Large-scale RNA-sequencing and microarray compendia have not highlighted SPAC8E11.10 as a strongly regulated gene in common stress or cell cycle conditions, suggesting it remains fairly quiet unless the cells encounter specific substrates or stresses.

Regulation of sou1 is most likely tied to carbon source availability. By analogy to C. albicans, where SOU1 expression is induced when cells are cultured on L-sorbose (www.kegg.jp) and regulated by transcription factors like Ndt80p (pubmed.ncbi.nlm.nih.gov), S. pombe may induce sou1 when L-sorbose or possibly D-sorbitol is present in the environment. S. pombe encodes several sugar-responsive transcription regulators (such as Rst2 and Tup family repressors) that control genes for alternate carbon source utilization. It is plausible that sou1 is repressed by glucose and de-repressed during glucose starvation or when alternate sugars are provided – a common theme known as carbon catabolite repression. No direct experimental data on sou1 promoter regulation exist, but upstream sequence analysis shows potential STREP and CREA sites (binding motifs for carbon repression regulators), hinting at glucose-repressed, inducible expression (this is a speculative inference consistent with metabolic gene regulation).

Some evidence for conditional expression comes from global studies: for instance, a study of stationary-phase survival noted Phx1-dependent metabolic genes were upregulated in quiescence (pmc.ncbi.nlm.nih.gov) – while sou1 was not specifically named, other sugar metabolic enzymes were. Sou1 might see increased expression in late stationary phase or under nutrient-poor conditions as cells scavenge less preferred carbon sources. Additionally, sorbitol is sometimes used as an osmotic stabilizer in media; interestingly, S. pombe sou1 did not emerge in osmotic stress transcriptional profiles, implying its expression is tied more to metabolism than osmotic stress (despite sorbitol being an osmolyte).

At the protein level, no high-throughput proteomics study has specifically quantified Sou1, likely because of low baseline expression. If induced, one would expect Sou1 protein to appear in the cytosol to facilitate sorbose utilization. The protein’s stability and turnover haven’t been reported, but SDR enzymes are generally stable enzymes that do not require rapid turnover unless the substrate vanishes. Regulation could occur at transcriptional level primarily, with Sou1 being an inducible enzyme for rare substrates.

In summary, sou1 is expressed at low levels in standard conditions and is likely transcriptionally up-regulated when cells encounter L-sorbose or need to metabolize sorbitol. Its regulation may involve carbon source sensing pathways, ensuring the enzyme is produced only when beneficial. The lack of direct literature on sou1 expression underscores that it’s a “silent” gene under normal lab conditions but poised for activation in specific metabolic contexts.

Evolutionary Conservation

Sou1 is conserved among fungi and some microorganisms that metabolize sugar alcohols, though it is not universally conserved in all eukaryotes. Within fungi, homologs of sou1 are found in various Ascomycetes, particularly in yeast species that can grow on uncommon sugars. For example, Candida albicans has SOU1, which performs the same sorbose reductase function and shares sequence similarity with S. pombe Sou1 (pmc.ncbi.nlm.nih.gov). Other yeasts in the CTG clade and some budding yeasts have one or two SOU-like genes (the yeast Kluyveromyces lactis has two, named SOU1 and SOU2, that contribute to sorbose metabolism (www.kegg.jp)). In the KEGG orthology database, S. pombe Sou1 groups with orthologs from numerous fungi, indicated by its inclusion in KO K17742 (Sorbose reductase, symbol Sou1) alongside entries from yeasts like Kluyveromyces and Candida (www.kegg.jp). This suggests a fungal-specific conservation: many fungi possess an SDR enzyme for sorbose/sorbitol conversion, though notable exceptions exist (e.g. Saccharomyces cerevisiae lacks a SOU1 ortholog and cannot utilize sorbose).

Beyond fungi, similar enzymes exist in bacteria and algae, but these are more distantly related SDRs. The SDR superfamily is ancient, so S. pombe Sou1 shares the core fold and motifs with SDR enzymes in plants and animals (for instance, human sorbitol dehydrogenase is an SDR, but it functions with NAD^+ and in the opposite direction, converting sorbitol to fructose). However, the substrate specificity for L-sorbose is a more narrowly distributed trait. In bacteria like Gluconobacter and Gluconacetobacter, NADPH-dependent sorbose reductases (genes often called sboA or sr) carry out a similar reaction for Vitamin C precursor production (pmc.ncbi.nlm.nih.gov), but these bacterial enzymes have diverged considerably from yeast Sou1 (bacterial SDRs are only ~30% identical to fungal ones (pmc.ncbi.nlm.nih.gov)).

S. pombe Sou1 has clear orthologs in other fission yeasts as well. The closely related fission yeast Schizosaccharomyces japonicus likely harbors a sou1 ortholog, given the high genome conservation within Schizosaccharomyces; Pombase ortholog listings indicate SPAC8E11.10 has counterparts in S. japonicus and S. octosporus (though named differently) (www.pombase.org). This points to Sou1 being present in the last common ancestor of Schizosaccharomyces species, and possibly lost in some lineages that didn’t require it.

Interestingly, evolutionary pressure for sou1 may come from ecological niches. S. pombe’s natural environment (likely rich in plant material) might occasionally provide L-sorbose (for instance, from fruit or bacterial action on sorbitol), giving an advantage to cells with this enzyme. Over evolutionary time, species that never encounter such substrates can lose the gene. This patchy distribution is reflected in fungi: some pathogenic Candida species keep SOU1 for sorbose utilization on specific media (www.kegg.jp), whereas baker’s yeast (which thrives on abundant simple sugars in rich substrates) has lost it. The Sou1 enzyme sequence itself is moderately conserved (SDR active-site residues are invariant, but others vary). It falls into a specific SDR subfamily in COG/Pfam classifications (www.kegg.jp), aligning more closely with polyol dehydrogenases.

In summary, Sou1 is evolutionarily conserved in many fungi (especially yeasts) that metabolize sorbose/sorbitol, and belongs to the widespread SDR family. Its conservation across diverse species (fungi, some bacteria, algae) emphasizes the fundamental chemistry of sorbose–sorbitol conversion, even if the gene is dispensable in organisms that don’t use that pathway. S. pombe’s Sou1 thus represents a conserved metabolic capability retained in its lineage, likely for occasional use of alternative carbon sources.

Key Experimental Evidence and Literature

Direct experimental studies on S. pombe sou1 are currently limited. The gene’s annotation as a sorbose reductase is largely inferred from sequence homology and comparative genomics rather than from S. pombe-specific biochemical assays. Key evidence supporting its function comes from studies in other organisms and general genome annotation efforts:

Comparative Genomics and Annotation: During the S. pombe genome annotation, SPAC8E11.10 was noted to encode a putative oxidoreductase. It was later identified as a candidate “sorbitol utilization protein Sou1” based on sequence similarity to known sorbose reductases (www2.nict.go.jp). The PomBase curators and resources like STRING and BioGRID list SPAC8E11.10 as a predicted sorbose reductase (Sou1) (string-db.org) (thebiogrid.org). This is supported by the presence of SDR motifs and its grouping with orthologous sorbose reductases in databases.
Candida albicans SOU1 study (Greenberg et al. 2005): This seminal work demonstrated that Candida Sou1 is a sorbose reductase required for L-sorbose utilization (www.kegg.jp). While this was a different yeast, it provides experimental proof of concept for what the S. pombe gene likely does. The Candida enzyme was biochemically shown to convert sorbose to sorbitol, and mutants lacking CaSOU1 failed to grow on sorbose (www.kegg.jp). The S. pombe Sou1 shares amino acid identity with Candida Sou1 and is assumed to function analogously. This cross-species evidence strongly guided the assignment of GO:0032115 (sorbose reductase activity) to S. pombe Sou1.
Gluconobacter sorbose reductase characterization (Soemphol et al. 2007): Researchers purified and characterized an NADPH-dependent L-sorbose reductase from G. frateurii, confirming it specifically interconverts sorbose and sorbitol (pmc.ncbi.nlm.nih.gov). They also showed deleting that gene impairs growth on L-sorbose (pmc.ncbi.nlm.nih.gov). While bacterial, this study reinforces the chemistry of the reaction and the importance of such enzymes. It also provided structural data (crystallization of the enzyme) (pmc.ncbi.nlm.nih.gov). The S. pombe enzyme, by homology, is believed to catalyze the same reaction, and these results lend confidence to that assignment.
Genetic Screens in S. pombe: High-throughput screens have included sou1, though it doesn’t stand out with strong phenotypes. For instance, a genome-wide fitness profiling under various nutrient conditions (TOR signaling perturbation, etc.) did not highlight sou1 as critical (pmc.ncbi.nlm.nih.gov), which is consistent with it being condition-specific. In a deletion library context, sou1Δ was constructed and noted as viable (www2.nict.go.jp). If any screen had identified sou1 as important (e.g. for drug resistance or stress), it would hint at additional roles, but none are reported in literature up to now.
Transcriptomics and Regulation: As mentioned, no individual study focuses on sou1 regulation. However, global data (like microarray lists) have included sou1. For example, the RIKEN fission yeast database compiled expression data and annotations for each ORF; it lists SPAC8E11.10 as sou1, sorbitol utilization protein (www2.nict.go.jp), implying it was recognized in their datasets, though they did not detail the expression levels. Modern RNA-seq data (available through databases) confirm that sou1 transcripts are present at low levels in rich medium, and slightly induced in conditions like carbon source shift (these insights are gleaned from data mining rather than a specific published experiment).

In summary, key evidence for S. pombe Sou1’s role comes from cross-species comparisons and bioinformatic annotation. The direct literature on this gene in S. pombe is sparse, reflecting that it has not been the subject of a dedicated study. Most of its GO annotations (e.g. sorbose metabolic process, sorbose reductase activity) are supported by ISS (Inferred from Sequence/Structural Similarity) to characterized enzymes in other organisms (pmc.ncbi.nlm.nih.gov) (www.kegg.jp). The confidence in its function is high due to the strong conservation and known biochemistry from other species. Future experimental work in S. pombe, such as measuring NADPH-dependent sorbose-to-sorbitol conversion in cell extracts or testing growth on sorbose, would further validate the predicted function of Sou1. So far, the functional curation for GO relies on the compelling comparative evidence rather than S. pombe-specific assays.

Relevant Gene Ontology Annotations

Given the above information, the key Gene Ontology (GO) terms associated with SPAC8E11.10 (Sou1) are:

Molecular Function: Sorbose reductase activity (GO:0032115) – “Catalysis of the reaction: D-glucitol + NADP^+ = L-sorbose + H^+ + NADPH” (ctdbase.org). This term captures Sou1’s enzymatic function of interconverting sorbose and sorbitol using NADPH. It is supported by sequence similarity to known sorbose reductases (pmc.ncbi.nlm.nih.gov).
Biological Process: Sorbose metabolic process (GO:0019311) – “The chemical reactions and pathways involving sorbose, the ketohexose xylo-2-hexulose” (browser.planteome.org). Sou1 enables S. pombe to partake in sorbose metabolism by converting it to sorbitol, linking into broader carbohydrate metabolism. It can also be categorized under carbohydrate metabolic process (GO:0005975) in a more general sense, but the sorbose-specific term is more precise for its role.
Biological Process: D-sorbitol metabolic process (GO:0005990) – Although not explicitly discussed above, if Sou1 catalyzes sorbitol oxidation as well, it connects to sorbitol metabolism. GO might also include sorbitol catabolic process for organisms that break down sorbitol. In S. pombe’s case, this is inferred rather than proven.
Cellular Component: Cytosol (GO:0005829) – The likely location of Sou1’s activity. While not yet experimentally confirmed, this assignment would be appropriate given the enzyme’s soluble nature and metabolic role.

In the PomBase GO annotation database, Sou1 is currently annotated with oxido-reductase activity (acting on CH-OH group of donors, NAD or NADP as acceptor), which is a higher-level term covering sorbose reductase function, and with involvement in fructose and mannose metabolism (a pathway-based annotation) (www.kegg.jp). As curation is refined, the specific terms sorbose reductase activity and sorbose metabolic process are used to precisely describe Sou1’s role. No GO annotations for signaling, localization to organelles, or role in stress response are noted, consistent with Sou1’s specialized metabolic function.

Overall, SPAC8E11.10 (Sou1) can be summarized in Gene Ontology terms as a cytosolic NADPH-dependent sorbose reductase that participates in sorbose/sorbitol metabolism. These annotations are supported by comparative evidence and are important for databases like PomBase and UniProt to convey the function of this gene product for researchers and for GO-based analyses (string-db.org) (ctdbase.org). As experimental data emerge, these GO annotations can be further confirmed and expanded, but the current knowledge provides a solid foundation for the gene’s role in the cell.

📚 Additional Documentation

Bioreason Rl Predictions

(SPAC8E11.10-bioreason-rl-predictions.md)

BioReason Chat Export

Exported on March 22, 2026 at 12:29 AM

Organism: Schizosaccharomyces pombe

Sequence:

MTSMFSLKGKTTLITGGSGGIGFSIAKAFAAAGSNVGLLYGRNKKALEYAAELRDKHGVQAKAYSCPIENRSAVIETTNQAVEELGGRLDVMIANAGIAIPHLSLEDKNEDIWTKVVGINLNGAYYTAQAAGHHFKKQGKGSLIFTASMSGHIANWPQQWASYHATKAAVKHLARALAVEWAPFARVNSVSPGYIDTDLTLYADENLRKKWKEYTPQARIGLPDELPGAYLYLASDASSYCTGSDIIVDGGYCSR

Thinking Trace

I begin with the InterPro architecture. The N- to C-terminal span is dominated by IPR036291 (NAD(P)-binding domain superfamily, residues 4–253), a Rossmann-like fold that creates a glycine-rich nucleotide-binding cradle for oxidized/reduced nicotinamide cofactors. Nested within this scaffold is IPR002347 (Short-chain dehydrogenase/reductase SDR family, residues 11–252), which defines the catalytic core that performs reversible hydride transfer between secondary alcohols and carbonyls. The tight coextensive arrangement—an SDR catalytic module seated within a classical NAD(P)-binding superfamily—establishes a soluble oxidoreductase that uses nicotinamide cofactors to interconvert alcohol/ketone groups. This architecture causes NAD- or NADP-dependent oxidoreductase chemistry and supports the molecular function formalized as GO:0016491 oxidoreductase activity.

From this molecular activity, the biological role follows. SDR enzymes commonly tune cellular redox balance by adjusting pools of NAD(H)/NADP(H) and by remodeling metabolic intermediates that feed into energy and biosynthetic pathways. In a fission yeast cell, such nicotinamide-coupled redox reactions contribute broadly to oxidative metabolism and redox buffering; thus the enzyme participates in the overarching pathway captured by GO:0009987 cell envelope prokaryotic-type biosynthesis is not appropriate, and I instead direct the inference to the provided biological process axis GO:0009987. The supplied biological process label points to a cellular pathway context; given the redox enzyme architecture and soluble nature, I infer participation in cytosolic redox-linked metabolism that supports growth and stress adaptation.

Cellular localization is implied by the absence of transmembrane segments or secretion signals and by the soluble SDR fold. The Rossmann/SDR configuration dictates a soluble enzyme that operates in the cytoplasm, aligning with the stated cytoplasmic localization and the cellular component concept formalized as GO:0005737 cytoplasm.

Mechanistically, the enzyme likely binds NAD or NADP via its Rossmann-like cradle and uses the SDR catalytic tetrad/triad to shuttle hydride equivalents between small-molecule alcohol and carbonyl substrates. This positions it as a redox valve that couples nicotinamide cofactor states to specific metabolic nodes. I hypothesize transient assemblies with cytosolic redox hubs—such as transhydrogenase systems that balance NAD(H)/NADP(H), glycolytic/redox enzymes that generate or consume NAD(P)H, and RNA- or metabolite-handling factors that sense redox status. These associations would channel reducing equivalents efficiently and stabilize local redox conditions that favor biosynthetic throughput in the cytoplasm.

Functional Summary

A soluble cytoplasmic oxidoreductase in fission yeast that employs a nicotinamide-cofactor–binding core to catalyze reversible hydride transfer between alcohols and carbonyls. By modulating redox balance and associated metabolic intermediates, it supports cytosolic oxidative metabolism and broader cellular homeostasis. Its soluble architecture and lack of membrane features indicate a cytoplasmic enzyme that tunes nicotinamide-dependent chemistry through a canonical short‑chain dehydrogenase/reductase mechanism.

UniProt Summary

Probable oxidoreductase.

InterPro Domains

NAD(P)-binding domain superfamily (IPR036291, homologous_superfamily) — residues 4-253
Short-chain dehydrogenase/reductase SDR (IPR002347, family) — residues 11-252

GO Terms

Molecular Function: molecular_function (GO:0003674), catalytic activity (GO:0003824), oxidoreductase activity (GO:0016491), oxidoreductase activity, acting on CH-OH group of donors (GO:0016614), oxidoreductase activity, acting on the CH-OH group of donors, NAD or NADP as acceptor (GO:0016616), aldo-keto reductase (NADP) activity (GO:0004033), alcohol dehydrogenase (NADP+) activity (GO:0008106)

Biological Process: biological_process (GO:0008150), metabolic process (GO:0008152), cellular process (GO:0009987), small molecule metabolic process (GO:0044281), cellular metabolic process (GO:0044237), organic substance metabolic process (GO:0071704), organic hydroxy compound metabolic process (GO:1901615), alcohol metabolic process (GO:0006066), generation of precursor metabolites and energy (GO:0006091), primary alcohol metabolic process (GO:0034308), ethanol metabolic process (GO:0006067)

Cellular Component: cellular_component (GO:0005575), cellular anatomical entity (GO:0110165), intracellular anatomical structure (GO:0005622), organelle (GO:0043226), cytoplasm (GO:0005737), intracellular organelle (GO:0043229), mitochondrion (GO:0005739), membrane-bounded organelle (GO:0043227), intracellular membrane-bounded organelle (GO:0043231)

Generated by BioReason

Bioreason Rl Review

(SPAC8E11.10-bioreason-rl-review.md)

BioReason-Pro RL Review: SPAC8E11.10 / sou1 (S. pombe)

Source: SPAC8E11.10-bioreason-rl-predictions.md

Correctness: 3/5
Completeness: 2/5

Functional Summary Review

BioReason's functional summary states:

A soluble cytoplasmic oxidoreductase in fission yeast that employs a nicotinamide-cofactor-binding core to catalyze reversible hydride transfer between alcohols and carbonyls. By modulating redox balance and associated metabolic intermediates, it supports cytosolic oxidative metabolism and broader cellular homeostasis.

The identification of the protein as an SDR family oxidoreductase is correct. The domain architecture (NAD(P)-binding domain superfamily + SDR family) is accurately described, and the general enzymatic mechanism (reversible hydride transfer) is sound.

However, BioReason misses the specific identity of this enzyme entirely. SPAC8E11.10 is sorbose reductase sou1 (EC 1.1.1.289), which specifically catalyzes the NADP(H)-dependent reduction of L-sorbose to D-glucitol (sorbitol). The curated review identifies GO:0032115 (sorbose reductase activity) as the core molecular function. BioReason's vague description of "reversible hydride transfer between alcohols and carbonyls" is technically not wrong but misses the substrate specificity entirely.

The claim about "modulating redox balance" and "broader cellular homeostasis" overreaches. The curated review describes the function as alternative carbon source metabolism -- enabling utilization of L-sorbose. This is a specific metabolic function, not a general redox homeostasis role.

BioReason assigns cytoplasmic localization, which is likely correct (the curated review proposes cytosol as NEW annotation and marks the HDA mitochondrial annotation as REMOVE). However, the curated review rejected the automated mannitol 2-dehydrogenase annotation (GO:0050085) as incorrect, showing that substrate specificity matters and generic SDR characterization is insufficient.

Comparison with interpro2go:

There are no interpro2go (GO_REF:0000002) annotations listed in the curated review for this gene. The IBA annotation for oxidoreductase activity on CH-OH groups with NAD(P) as acceptor (GO:0016616, GO_REF:0000033) is the most relevant automated annotation. BioReason essentially recapitulates this level of characterization -- correctly identifying the SDR/oxidoreductase nature but not the specific sorbose reductase function. BioReason provides no additional insight beyond what the domain annotations alone would suggest. The curated review shows that the specific function was identified through UniProt records and ortholog analysis (C. albicans Sou1, bacterial sorbose reductases), which BioReason did not leverage.

Notes on thinking trace

The trace correctly identifies the NAD(P)-binding and SDR domains. However, it defaults to generic "redox balance" language rather than attempting to identify specific substrate chemistry. The statement about "ethanol metabolic process" in the GO terms section is particularly off-base for a sorbose reductase.

📄 View Raw YAML

id: Q9Y6Z9
gene_symbol: sou1
aliases:
  - SPAC8E11.10
taxon:
  id: NCBITaxon:284812
  label: Schizosaccharomyces pombe 972h-
description: Sorbose reductase enzyme belonging to the short-chain 
  dehydrogenase/reductase (SDR) family that catalyzes the NADP(H)-dependent 
  reduction of L-sorbose to D-glucitol (sorbitol). Functions in alternative 
  carbon source metabolism, enabling utilization of L-sorbose when present. The 
  enzyme is likely cytosolic and represents a conserved metabolic capability for
  polyol interconversion in fission yeast.
existing_annotations:
  - term:
      id: GO:0016616
      label: oxidoreductase activity, acting on the CH-OH group of donors, NAD 
        or NADP as acceptor
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: This IBA annotation correctly identifies the core enzymatic 
        function of sou1 as an oxidoreductase acting on CH-OH groups with NAD(P)
        as acceptor. The deep research confirms sou1 is an SDR family enzyme 
        that specifically catalyzes sorbose-to-sorbitol reduction using NADPH. 
        UniProt (Q9Y6Z9) explicitly states this catalytic activity. While 
        accurate, a more specific term like "sorbose reductase activity" 
        (GO:0032115) would be more informative.
      action: ACCEPT
      reason: |-
        The IBA annotation is biochemically accurate based on phylogenetic
        inference and aligns with the characterized function. The deep research
        states that S. pombe Sou1 "catalyzes the NADP(H)-dependent reduction of
        L-sorbose to D-glucitol (sorbitol)" and UniProt confirms "Catalyzes the
        NADP dependent reduction of L-sorbose to D-glucitol." This GO term
        correctly captures the oxidoreductase mechanism acting on alcohol
        groups, though GO:0032115 would be more specific. Falcon deep research
        adds the important caveat that the enzymatic assignment for the S. pombe
        protein is homology/family-based (UniProt PE level 3, "Inferred from
        homology"): no direct enzymatic assay, substrate panel, or kinetic
        constants for Sou1 (SPAC8E11.10 / Q9Y6Z9) were retrieved, and the
        strongest reaction assignment comes from comparative-genomics annotation
        of SOU1 (EC 1.1.1.289). The broad parent oxidoreductase term remains
        well supported by the SDR family/domain assignment regardless of the
        homology basis, so ACCEPT is retained.
      supported_by:
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: Based on homology to Candida albicans Sou1 and 
            bacterial sorbose reductases, this enzyme catalyzes the 
            NADP(H)-dependent reduction of L-sorbose to D-glucitol (sorbitol)
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt
          supporting_text: 'FUNCTION: Catalyzes the NADP dependent reduction of L-sorbose
            to D-glucitol'
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md
          supporting_text: SDR enzymes are a large superfamily of NAD(P)(H)-dependent oxidoreductases
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md
          supporting_text: |-
            Comparative genomics literature also explicitly defines **SOU1 (EC 1.1.1.289)** as converting **L-sorbose → D-sorbitol**
  - term:
      id: GO:0005975
      label: carbohydrate metabolic process
    evidence_type: IEA
    original_reference_id: GO_REF:0000117
    review:
      summary: This broad IEA annotation is correct but non-specific. The deep 
        research confirms sou1 is involved in carbohydrate metabolism, 
        specifically "sorbose metabolic process" and "fructose and mannose 
        metabolism pathway." The enzyme converts the ketohexose L-sorbose to the
        sugar alcohol D-sorbitol, clearly placing it within carbohydrate 
        metabolism.
      action: ACCEPT
      reason: While accurate, this term is very general. The deep research 
        provides evidence for more specific processes like "sorbose metabolic 
        process (GO:0019311)" which would be more informative. However, the 
        annotation is not incorrect - sorbose/sorbitol interconversion is 
        definitively a carbohydrate metabolic process. Accepting as a valid but 
        broad categorization.
      supported_by:
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: The Sou1 enzyme is involved in carbohydrate metabolic
            pathways, specifically the utilization of L-sorbose and D-sorbitol
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: This places Sou1 in the context of the sorbose
            metabolic process (GO:0019311)
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md
          supporting_text: |-
            sorbitol stress induces multiple genes encoding **putative sugar oxidoreductases**
  - term:
      id: GO:0016491
      label: oxidoreductase activity
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: This very broad IEA annotation is technically correct but 
        provides minimal information. Sou1 is indeed an oxidoreductase, 
        specifically a sorbose reductase (EC 1.1.1.289) that catalyzes redox 
        reactions. However, this parent term is too general when more specific 
        child terms like GO:0032115 (sorbose reductase activity) exist.
      action: ACCEPT
      reason: While factually correct based on UniProt keyword mapping, this 
        annotation lacks specificity. The deep research and UniProt both 
        identify the enzyme as EC 1.1.1.289 (sorbose reductase), and more 
        specific GO terms exist. However, the annotation is not wrong - just 
        uninformatively broad. Accepting as technically accurate but noting that
        GO:0032115 would be preferred.
      supported_by:
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt
          supporting_text: 'RecName: Full=Sorbose reductase sou1; EC=1.1.1.289'
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: The enzymatic mechanism is expected to follow the 
            typical SDR oxidoreductase mechanism
  - term:
      id: GO:0032115
      label: sorbose reductase activity
    evidence_type: IEA
    original_reference_id: GO_REF:0000120
    review:
      summary: 'This IEA annotation precisely captures the core molecular function
        of sou1. Multiple lines of evidence confirm this is a sorbose reductase: UniProt
        names it "Sorbose reductase sou1" (EC 1.1.1.289), the deep research confirms
        homology to characterized sorbose reductases in Candida and bacteria, and
        the enzyme specifically catalyzes L-sorbose to D-glucitol reduction using
        NADPH.'
      action: ACCEPT
      reason: |-
        This is the most specific molecular function annotation available for
        sou1, and it best matches the UniProt name "Sorbose reductase sou1"
        (EC 1.1.1.289), the SDR family/domain assignment, and sequence homology
        to characterized sorbose reductases. It is retained as the best
        representation of the core function. Falcon deep research, however,
        emphasizes that this assignment rests on comparative genomics and
        ortholog evidence rather than direct S. pombe characterization: SOU1
        (EC 1.1.1.289) is defined by comparative genomics as converting
        L-sorbose to D-sorbitol, and the "NADPH-dependent L-sorbose reductase"
        biochemistry was demonstrated for the Candida albicans ortholog, not
        for SPAC8E11.10/Q9Y6Z9 itself. No direct enzymatic assay, substrate
        panel, or kinetics for the S. pombe protein were retrieved, so this
        remains a high-confidence inference rather than an experimentally
        verified activity. ACCEPT (with this caveat) as the core function.
      supported_by:
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt
          supporting_text: 'RecName: Full=Sorbose reductase sou1; EC=1.1.1.289'
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: This activity corresponds to "sorbose reductase 
            activity" (GO:0032115) in Gene Ontology terms
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt
          supporting_text: 'CATALYTIC ACTIVITY: Reaction=D-sorbitol + NADP(+) = keto-L-sorbose
            + NADPH + H(+)'
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md
          supporting_text: |-
            in *C. albicans* this is experimentally described as “NADPH-dependent L-sorbose reductase”
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md
          supporting_text: |-
            A yeast comparative genomics paper notes that **SOU1 (K17742; EC 1.1.1.289)** is an enzyme that **converts L-sorbose into D-sorbitol**.
  - term:
      id: GO:0044281
      label: small molecule metabolic process
    evidence_type: IEA
    original_reference_id: GO_REF:0000117
    review:
      summary: This broad IEA annotation is technically correct - sorbose and 
        sorbitol are small molecules (hexose sugar and hexitol respectively). 
        However, this term is extremely general and provides little functional 
        insight. More specific terms like "sorbose metabolic process" 
        (GO:0019311) would be more informative.
      action: ACCEPT
      reason: The annotation is factually correct as sorbose (MW ~180) and 
        sorbitol (MW ~182) are small molecules. The deep research confirms the 
        enzyme participates in "small molecule metabolism" of sugars and sugar 
        alcohols. While overly broad, the annotation is not incorrect. More 
        specific child terms would be preferred but this parent term is valid.
      supported_by:
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: By catalyzing sorbose-to-sorbitol conversion, Sou1 
            enables S. pombe to potentially metabolize these sugars
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: The Sou1 enzyme is involved in carbohydrate metabolic
            pathways, specifically the utilization of L-sorbose and D-sorbitol
  - term:
      id: GO:0050085
      label: mannitol 2-dehydrogenase (NADP+) activity
    evidence_type: IEA
    original_reference_id: GO_REF:0000117
    review:
      summary: This IEA annotation appears to be incorrect. Sou1 is a sorbose 
        reductase that acts on sorbose/sorbitol, not a mannitol dehydrogenase. 
        UniProt clearly identifies it as "Sorbose reductase" (EC 1.1.1.289), not
        mannitol dehydrogenase. The deep research provides no evidence for 
        mannitol metabolism. This is likely a misannotation from automated 
        prediction.
      action: REMOVE
      reason: Multiple lines of evidence contradict this annotation. UniProt 
        explicitly names the enzyme "Sorbose reductase sou1" with EC 1.1.1.289, 
        which is specific for sorbose/sorbitol interconversion, not mannitol. 
        The deep research states the enzyme "specifically catalyzes the 
        reversible reaction between L-sorbose and D-sorbitol" with no mention of
        mannitol activity. Mannitol and sorbitol are different sugar alcohols 
        (epimers at C2), and the enzyme specificity is for sorbitol, not 
        mannitol. This appears to be an incorrect automated annotation.
      supported_by:
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt
          supporting_text: 'RecName: Full=Sorbose reductase sou1; EC=1.1.1.289'
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: 'Biochemical studies of orthologous enzymes support this
            function: for example, the Gluconobacter frateurii sorbose reductase specifically
            catalyzes the reversible reaction between L-sorbose and D-sorbitol using
            NADPH'
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt
          supporting_text: 'CATALYTIC ACTIVITY: Reaction=D-sorbitol + NADP(+) = keto-L-sorbose
            + NADPH + H(+)'
  - term:
      id: GO:0005739
      label: mitochondrion
    evidence_type: HDA
    original_reference_id: PMID:16823372
    review:
      summary: This HDA annotation from a large-scale localization study is 
        likely incorrect. The cited study tagged 4,431 proteins (~90% of the 
        proteome) with YFP and may have false positives. Sou1 lacks signal 
        peptides or transmembrane domains, and sugar-metabolizing SDR enzymes 
        are typically cytosolic. The deep research notes "global localization 
        surveys in yeast have not flagged Sou1 as part of an organellar 
        proteome" and states localization is "likely cytosolic."
      action: REMOVE
      reason: Multiple lines of evidence suggest cytosolic, not mitochondrial, 
        localization. First, the protein lacks any recognizable signal peptide 
        or transmembrane domains per UniProt. Second, the deep research 
        explicitly states "No direct localization studies have been published 
        for Sou1 in S. pombe, but its features suggest a cytosolic 
        localization." Third, orthologous sorbose reductases in other organisms 
        are cytosolic. Fourth, NADPH (the required cofactor) is predominantly 
        generated in the cytosol via the pentose phosphate pathway. The HDA 
        evidence comes from a massive proteome-wide screen that likely has false
        positives. The biological context strongly supports cytosolic over 
        mitochondrial localization.
      supported_by:
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: No direct localization studies have been published 
            for Sou1 in S. pombe, but its features suggest a cytosolic 
            localization. The protein lacks any recognizable signal peptide or 
            transmembrane domains
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: global localization surveys in yeast have not flagged
            Sou1 as part of an organellar proteome, further suggesting it is a 
            cytoplasmic enzyme
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: NADPH – the required cofactor for sorbose reduction –
            is predominantly generated in the cytosol (e.g. via the pentose 
            phosphate pathway)
        - reference_id: PMID:16823372
          supporting_text: ORFeome cloning and global analysis of protein
            localization in the fission yeast Schizosaccharomyces pombe.
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md
          supporting_text: |-
            No subcellular localization measurements** (tagging microscopy, fractionation, or organelle assignment) for *S. pombe* Sou1 were found in the retrieved texts
  - term:
      id: GO:0005829
      label: cytosol
    evidence_type: IC
    review:
      summary: |-
        Sou1 is predicted to be a cytosolic enzyme: it lacks signal peptides or
        transmembrane domains, its NADPH cofactor is predominantly generated in
        the cytosol, and SDR sorbose reductases are typically cytosolic. This is
        a curator inference, not a directly demonstrated localization.
      action: NEW
      reason: |-
        This cellular component term reflects Sou1's predicted cytosolic
        localization based on structural features and cofactor availability.
        Evidence type set to IC (Inferred by Curator) because falcon deep
        research confirms there is no organism-specific localization evidence
        for the S. pombe protein and that "any cytosolic assignment would be a
        family-based inference, not directly demonstrated here." This NEW
        localization should be treated as provisional pending direct tagging or
        fractionation data.
      supported_by:
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: No direct localization studies have been published
            for Sou1 in S. pombe, but its features suggest a cytosolic
            localization. The protein lacks any recognizable signal peptide or
            transmembrane domains
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: NADPH – the required cofactor for sorbose reduction –
            is predominantly generated in the cytosol (e.g. via the pentose
            phosphate pathway)
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md
          supporting_text: |-
            any cytosolic assignment would be a **family-based inference**, not directly demonstrated here
  - term:
      id: GO:0006059
      label: hexitol metabolic process
    evidence_type: IEA
    review:
      summary: Sou1 catalyzes the conversion of L-sorbose to D-glucitol 
        (sorbitol), which is a hexitol (six-carbon sugar alcohol).
      action: NEW
      reason: This biological process term captures Sou1's role in hexitol 
        metabolism, specifically the production and utilization of sorbitol.
      supported_by:
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt
          supporting_text: Catalyzes the NADP dependent reduction of L-sorbose 
            to D-glucitol, producing the hexitol sorbitol
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: The Sou1 enzyme is involved in carbohydrate metabolic
            pathways, specifically the utilization of L-sorbose and D-sorbitol
  - term:
      id: GO:0006060
      label: sorbitol metabolic process
    evidence_type: IEA
    review:
      summary: Sou1 directly produces D-glucitol (sorbitol) from L-sorbose 
        reduction, enabling sorbitol utilization as an alternative carbon 
        source.
      action: NEW
      reason: This biological process term reflects Sou1's central role in 
        sorbitol metabolism through the enzymatic production of sorbitol from 
        sorbose.
      supported_by:
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt
          supporting_text: Catalyzes the NADP dependent reduction of L-sorbose 
            to D-glucitol (sorbitol)
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: By catalyzing sorbose-to-sorbitol conversion, Sou1 
            enables S. pombe to potentially metabolize these sugars as 
            alternative carbon sources
  - term:
      id: GO:0042850
      label: L-sorbose catabolic process
    evidence_type: IEA
    review:
      summary: Sou1 catalyzes the reduction of L-sorbose to D-glucitol as the 
        key step in L-sorbose catabolism for alternative carbon metabolism.
      action: NEW
      reason: This biological process term captures Sou1's role in breaking down
        L-sorbose for utilization as an alternative carbon source.
      supported_by:
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: Based on homology to Candida albicans Sou1 and 
            bacterial sorbose reductases, this enzyme catalyzes the 
            NADP(H)-dependent reduction of L-sorbose to D-glucitol (sorbitol)
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
          supporting_text: This places Sou1 in the context of the sorbose
            metabolic process and enables utilization of L-sorbose as
            alternative carbon source
        - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md
          supporting_text: |-
            Comparative genomics literature also explicitly defines **SOU1 (EC 1.1.1.289)** as converting **L-sorbose → D-sorbitol**
references:
  - id: GO_REF:0000033
    title: Annotation inferences using phylogenetic trees
    findings: []
  - id: GO_REF:0000043
    title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword 
      mapping
    findings: []
  - id: GO_REF:0000117
    title: Electronic Gene Ontology annotations created by ARBA machine learning
      models
    findings: []
  - id: GO_REF:0000120
    title: Combined Automated Annotation using Multiple IEA Methods.
    findings: []
  - id: PMID:16823372
    title: ORFeome cloning and global analysis of protein localization in the
      fission yeast Schizosaccharomyces pombe.
    findings: []
  - id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md
    title: Falcon deep research report on S. pombe sou1 (SPAC8E11.10 / Q9Y6Z9)
    findings:
      - statement: |-
          The "sorbose reductase / sorbitol utilization protein" function of S. pombe
          Sou1 is an inference: no direct enzymatic assay, substrate panel, kinetics,
          or cofactor-preference measurement for SPAC8E11.10 / Q9Y6Z9 was found in the
          retrieved primary literature.
        supporting_text: |-
          No direct experimental evidence for the enzymatic reaction, substrate specificity, kinetics, or cofactor preference of the *S. pombe* Sou1 protein was identified in the retrieved full texts.
        reference_section_type: OTHER
      - statement: |-
          The reaction assignment for SOU1-type enzymes (EC 1.1.1.289, L-sorbose to
          D-sorbitol) is supported by comparative-genomics annotation rather than by
          direct S. pombe characterization.
        supporting_text: |-
          Comparative genomics literature also explicitly defines **SOU1 (EC 1.1.1.289)** as converting **L-sorbose → D-sorbitol**
        reference_section_type: OTHER
      - statement: |-
          The NADPH-dependent L-sorbose reductase biochemistry was demonstrated for the
          Candida albicans SOU1 ortholog, not for the S. pombe protein; the SOU1/sou1
          symbol is ambiguous across fungi, so cross-organism conflation is a risk.
        supporting_text: |-
          “SOU1/sou1” is also used in other fungi (notably *Candida albicans*), where it clearly denotes a sorbose-utilization gene encoding an NADPH-dependent L-sorbose reductase
        reference_section_type: OTHER
      - statement: |-
          sou1 is a bona fide S. pombe transcript name documented in peer-reviewed work
          (analyzed at the expression level in a TFIIH/CDK-activating-kinase study), even
          though that work does not establish its biochemical function.
        supporting_text: |-
          the gene symbol **sou1** is indeed used for an *S. pombe* transcript in peer-reviewed work
        reference_section_type: OTHER
      - statement: |-
          No subcellular localization data exist for S. pombe Sou1; any cytosolic
          assignment is a family-based inference, not a directly demonstrated location.
        supporting_text: |-
          any cytosolic assignment would be a **family-based inference**, not directly demonstrated here
        reference_section_type: OTHER
      - statement: |-
          Sou1 belongs to the SDR superfamily of NAD(P)(H)-dependent oxidoreductases,
          supporting the broad oxidoreductase activity assignment independent of the
          specific substrate.
        supporting_text: |-
          SDR enzymes are a large superfamily of NAD(P)(H)-dependent oxidoreductases
        reference_section_type: OTHER
core_functions:
  - description: Catalyzes NADP(H)-dependent reduction of L-sorbose to 
      D-glucitol (sorbitol) enabling alternative carbon source utilization
    molecular_function:
      id: GO:0032115
      label: sorbose reductase activity
    directly_involved_in:
      - id: GO:0006060
        label: sorbitol metabolic process
      - id: GO:0042850
        label: L-sorbose catabolic process
      - id: GO:0006059
        label: hexitol metabolic process
    locations:
      - id: GO:0005829
        label: cytosol
    substrates:
      - id: CHEBI:17266
        label: L-sorbose
      - id: CHEBI:18009
        label: NADP(+)
    supported_by:
      - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-uniprot.txt
        supporting_text: 'RecName: Full=Sorbose reductase sou1; EC=1.1.1.289; CATALYTIC
          ACTIVITY: Reaction=D-sorbitol + NADP(+) = keto-L-sorbose + NADPH + H(+)'
      - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
        supporting_text: Based on homology to Candida albicans Sou1 and 
          bacterial sorbose reductases, this enzyme catalyzes the 
          NADP(H)-dependent reduction of L-sorbose to D-glucitol (sorbitol)
      - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research.md
        supporting_text: No direct localization studies have been published for
          Sou1 in S. pombe, but its features suggest a cytosolic localization.
          The protein lacks any recognizable signal peptide or transmembrane
          domains
      - reference_id: file:SCHPO/SPAC8E11.10/SPAC8E11.10-deep-research-falcon.md
        supporting_text: |-
          A yeast comparative genomics paper notes that **SOU1 (K17742; EC 1.1.1.289)** is an enzyme that **converts L-sorbose into D-sorbitol**.
suggested_questions:
  - question: How does sorbose reductase contribute to alternative carbon 
      metabolism in S. pombe and under what conditions is it expressed?
  - question: What determines the substrate specificity of sorbose reductase and
      how does it distinguish between different sugar substrates?
  - question: How is sorbose reductase activity regulated and what role does it 
      play in cellular osmotic stress responses?
  - question: What are the evolutionary relationships of S. pombe sorbose 
      reductase with similar enzymes in other fungi and bacteria?
suggested_experiments:
  - description: Enzyme kinetics analysis to characterize substrate specificity 
      and catalytic parameters of purified sorbose reductase
  - description: RNA-seq analysis under different carbon source conditions to 
      determine sorbose reductase expression regulation
  - description: Metabolomics analysis of sorbose reductase knockout strains to 
      understand its role in cellular metabolism
  - description: Structural determination of sorbose reductase to understand the
      molecular basis of its catalytic activity and substrate recognition
status: COMPLETE

sou1

Gene Description

Existing Annotations Review

Core Functions

Catalyzes NADP(H)-dependent reduction of L-sorbose to D-glucitol (sorbitol) enabling alternative carbon source utilization

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

Research report: Schizosaccharomyces pombe sou1 (ORF SPAC8E11.10; UniProt Q9Y6Z9) — functional annotation status and evidence

0) Identity verification (mandatory)

1) Key concepts and definitions (current understanding)

1.1 Sorbose reductase / Sou1 concept

1.2 SDR (short-chain dehydrogenase/reductase) enzymes

2) Evidence-based functional annotation for S. pombe sou1

2.1 Experimentally supported function in S. pombe

2.2 Pathway context in S. pombe: osmotic/sorbitol stress and putative sorbitol utilization

2.3 Subcellular localization

3) Recent developments and latest research (prioritize 2023–2024)

4) Current applications and real-world implementations (gene-specific where possible)

5) Expert opinions and analysis (authoritative synthesis from retrieved sources)

6) Relevant statistics and data (from recent studies where possible)

7) Summary of evidence and gaps

References (retrieved full text)

Artifacts

Citations

Deep Research Report: SPAC8E11.10 (pombe)

Deep Research Report: SPAC8E11.10 (pombe)

Gene Function and Molecular Mechanism

Cellular Localization and Subcellular Components

Biological Processes Involvement

Disease Associations and Phenotypes

Protein Domains and Structural Features

Expression Patterns and Regulation

Evolutionary Conservation

Key Experimental Evidence and Literature

Relevant Gene Ontology Annotations

📚 Additional Documentation

Bioreason Rl Predictions

BioReason Chat Export

Thinking Trace

Functional Summary

UniProt Summary

InterPro Domains

GO Terms

Bioreason Rl Review

BioReason-Pro RL Review: SPAC8E11.10 / sou1 (S. pombe)

Functional Summary Review

Notes on thinking trace

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