CelE (CtCel5C-CE2) is a multifunctional enzyme involved in plant cell wall degradation. It contains an N-terminal GH5 cellulase domain (CtCel5C), a central type I dockerin module for cellulosome integration, and a C-terminal CE2 esterase domain (CtCE2). The GH5 domain displays endo-1,4-beta-glucanase activity against cellulose, beta-glucan, and CMC. The CE2 domain exhibits both acetylxylan esterase and glucomannan deacetylase activities, with strong preference for glucomannan. Uniquely, the CE2 domain also functions as a cellulose-binding module through its catalytic site region, potentiating the cellulase activity of the appended GH5 domain on recalcitrant substrates.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0000272
polysaccharide catabolic process
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: This broad biological process annotation is supported by the established functions of CelE in degrading cellulose, xylan, and glucomannan - all plant cell wall polysaccharides (PMID:19338387, PMID:3066698).
Reason: CelE functions in the catabolism of multiple polysaccharides including cellulose, xylan, and glucomannan. This general term correctly captures the enzyme's role in polysaccharide breakdown, though more specific terms (cellulose catabolic process, xylan catabolic process, glucomannan catabolic process) provide greater specificity and are also annotated.
Supporting Evidence:
PMID:19338387
CtCE2 catalyses deacetylation of noncellulosic plant structural polysaccharides to deprotect these substrates for attack by other enzymes
PMID:3066698
The complete nucleotide sequence of the Clostridium thermocellum celE gene, coding for an endo-beta-1,4-glucanase (endoglucanase E; EGE) with xylan-hydrolysing activity has been determined.
file:ACET2/P10477/P10477-deep-research-falcon.md
CelE is a bifunctional enzyme with both cellulase and esterase domains
|
|
GO:0003824
catalytic activity
|
IEA
GO_REF:0000043 |
KEEP AS NON CORE |
Summary: This is a very general molecular function term that is true but uninformative. CelE has well-characterized specific catalytic activities including cellulase (EC 3.2.1.4) and acetylxylan esterase (EC 3.1.1.72) activities.
Reason: While technically correct, this term is too general to be informative. The specific catalytic activities (cellulase activity GO:0008810, acetylxylan esterase activity GO:0046555) are far more useful annotations. This annotation can be retained as a parent term but should not be considered a core annotation.
|
|
GO:0004553
hydrolase activity, hydrolyzing O-glycosyl compounds
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: This annotation correctly captures the glycoside hydrolase activity of the GH5 domain. The enzyme hydrolyzes beta-1,4-glucosidic linkages in cellulose and beta-glucan (PMID:3066698, PMID:1991028).
Reason: The GH5 cellulase domain of CelE catalyzes hydrolysis of O-glycosyl bonds in cellulose. This is an accurate parent term for the more specific cellulase activity.
Supporting Evidence:
PMID:3066698
coding for an endo-beta-1,4-glucanase (endoglucanase E; EGE)
|
|
GO:0005576
extracellular region
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: CelE is a secreted protein that functions as part of the extracellular cellulosome complex. The protein has a signal peptide (residues 1-34) and integrates into the cellulosome via its dockerin domain.
Reason: The UniProt record indicates the protein is secreted (signal peptide residues 1-34), and the protein functions in the extracellular cellulosome complex. The dockerin domain mediates integration into this extracellular multi-enzyme complex.
Supporting Evidence:
PMID:19338387
The enzyme also contains a type I dockerin module that, by binding to cohesin modules in the scaffoldin protein, incorporates CtCel5C-CE2 into the multienzyme plant cell-wall-degrading complex known as the cellulosome
|
|
GO:0005975
carbohydrate metabolic process
|
IEA
GO_REF:0000002 |
KEEP AS NON CORE |
Summary: This very broad biological process term is accurate but provides minimal specificity. The enzyme is involved in carbohydrate catabolism, specifically of polysaccharides.
Reason: While technically correct, this is a very high-level term. The more specific terms (cellulose catabolic process, xylan catabolic process, glucomannan catabolic process) provide much better functional annotation.
|
|
GO:0008810
cellulase activity
|
IEA
GO_REF:0000003 |
ACCEPT |
Summary: Cellulase activity is a core function of CelE, demonstrated through biochemical assays showing activity against CMC and barley beta-glucan (PMID:3066698, PMID:1991028). This activity is localized to the N-terminal GH5 domain (CtCel5C).
Reason: This is a core molecular function of CelE. The enzyme has EC 3.2.1.4 activity confirmed by direct experimental evidence. The GH5 domain catalyzes endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose.
Supporting Evidence:
PMID:3066698
coding for an endo-beta-1,4-glucanase (endoglucanase E; EGE)
|
|
GO:0016787
hydrolase activity
|
IEA
GO_REF:0000043 |
KEEP AS NON CORE |
Summary: CelE is a hydrolase with both glycosidase and esterase activities. This broad term is accurate but not specific.
Reason: This is a parent term that is technically correct but uninformative. The specific hydrolase activities (cellulase, acetylxylan esterase) are better annotations.
|
|
GO:0016788
hydrolase activity, acting on ester bonds
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: The CE2 domain of CelE has well-characterized esterase activity, catalyzing deacetylation of xylan and glucomannan (PMID:19338387).
Reason: This correctly captures the esterase activity of the CE2 domain. The enzyme hydrolyzes acetyl ester bonds in acetylated polysaccharides. More specific terms (acetylxylan esterase activity) provide additional detail.
Supporting Evidence:
PMID:19338387
All of these CE2 enzymes act as acetyl esterases, releasing acetate from activated artificial substrates such as 4-nitrophenyl acetate (4-NPAc; see Table 1) and, to different extents, the acetylated plant polysaccharides xylan and glucomannan
|
|
GO:0016798
hydrolase activity, acting on glycosyl bonds
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: This annotation correctly captures the glycoside hydrolase activity of the GH5 domain, which cleaves beta-1,4-glucosidic bonds in cellulose.
Reason: The GH5 domain of CelE is a glycoside hydrolase that cleaves glycosyl bonds. This is a parent term for the more specific cellulase activity annotation.
Supporting Evidence:
PMID:3066698
coding for an endo-beta-1,4-glucanase
|
|
GO:0030245
cellulose catabolic process
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: CelE participates in cellulose degradation through its GH5 cellulase domain, which hydrolyzes beta-1,4-glucosidic linkages in cellulose. The CE2 domain further enhances this activity by binding to cellulose and bringing the enzyme into contact with its substrate (PMID:19338387, PMID:1991028).
Reason: This is a core biological process annotation. CelE is a cellulosome component that directly participates in cellulose catabolism through its cellulase activity and cellulose-binding function.
Supporting Evidence:
PMID:19338387
it also acts as a cellulose-binding domain, which promotes the activity of the appended cellulase on recalcitrant substrates
|
|
GO:0046555
acetylxylan esterase activity
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: The CE2 domain of CelE has acetylxylan esterase activity (EC 3.1.1.72), catalyzing deacetylation of xylan (PMID:19338387). Kinetic parameters show KM of 2.7 mM and kcat of 12 min-1 for acetylated birchwood xylan.
Reason: This is a core molecular function of the CE2 domain. The enzyme catalyzes deacetylation of xylan, removing acetyl groups that protect the xylan backbone from degradation by other enzymes.
Supporting Evidence:
PMID:19338387
CtCE2 and CjCE2B exhibit a significant preference for acetylated glucomannan over xylan
|
|
GO:0046872
metal ion binding
|
IEA
GO_REF:0000043 |
MODIFY |
Summary: The dockerin domain of CelE contains calcium-binding sites that are essential for its function in binding to cohesin domains of the scaffoldin protein. Multiple calcium-binding residues are annotated in the UniProt record (residues 415-462).
Reason: While this annotation is technically correct, it would be more informative to use the more specific term GO:0005509 (calcium ion binding), as the metal binding is specifically to calcium ions in the dockerin domain.
Proposed replacements:
calcium ion binding
|
|
GO:0052689
carboxylic ester hydrolase activity
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: The CE2 domain hydrolyzes carboxylic esters (acetyl groups) from polysaccharides. This is consistent with its acetylxylan esterase and glucomannan deacetylase activities.
Reason: This is an accurate parent term for the esterase activity. The CE2 domain catalyzes hydrolysis of acetyl ester bonds, releasing acetate from polysaccharide substrates.
Supporting Evidence:
PMID:19338387
The esterases appear specific for acetyl groups
|
|
GO:2000884
glucomannan catabolic process
|
IEA
GO_REF:0000117 |
ACCEPT |
Summary: CelE participates in glucomannan catabolism through deacetylation of acetylated glucomannan by its CE2 domain. The enzyme shows preference for glucomannan over xylan, with KM of 0.019 mM (PMID:19338387).
Reason: This is a core biological process annotation. The CE2 domain deacetylates glucomannan, removing acetyl groups that protect the polysaccharide from degradation. The very low KM indicates high affinity for this substrate.
Supporting Evidence:
PMID:19338387
CtCE2 and CjCE2B exhibit a significant preference for acetylated glucomannan over xylan
|
|
GO:0045493
xylan catabolic process
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: CelE participates in xylan catabolism through both its xylanase activity (noted in PMID:3066698) and its acetylxylan esterase activity that deacetylates xylan to make it accessible to other enzymes (PMID:19338387).
Reason: This is a core biological process annotation. The original characterization noted xylan-hydrolyzing activity, and the CE2 domain deacetylates xylan, contributing to xylan degradation.
Supporting Evidence:
PMID:3066698
an endo-beta-1,4-glucanase (endoglucanase E; EGE) with xylan-hydrolysing activity
PMID:19338387
CtCE2 catalyses deacetylation of noncellulosic plant structural polysaccharides to deprotect these substrates for attack by other enzymes
|
|
GO:0008810
cellulase activity
|
IDA
PMID:3066698 Conserved reiterated domains in Clostridium thermocellum end... |
ACCEPT |
Summary: Direct experimental evidence from the original characterization of CelE demonstrates cellulase activity against cellulose substrates (PMID:3066698).
Reason: This IDA annotation is strongly supported by the original biochemical characterization of CelE as an endoglucanase. This is a core molecular function.
Supporting Evidence:
PMID:3066698
coding for an endo-beta-1,4-glucanase (endoglucanase E; EGE)
|
|
GO:0030245
cellulose catabolic process
|
IDA
PMID:3066698 Conserved reiterated domains in Clostridium thermocellum end... |
ACCEPT |
Summary: The original characterization established CelE's role in cellulose degradation.
Reason: This IDA annotation is appropriate based on the biochemical evidence for cellulase activity and the enzyme's role in the cellulosome complex.
Supporting Evidence:
PMID:3066698
coding for an endo-beta-1,4-glucanase
|
|
GO:0030248
cellulose binding
|
IDA
PMID:19338387 The active site of a carbohydrate esterase displays divergen... |
ACCEPT |
Summary: The CE2 domain of CelE binds cellulose through a unique mechanism involving its catalytic site region. ITC measurements show KD of 33 uM for cellohexaose. This binding potentiates the activity of the appended cellulase domain on recalcitrant substrates (PMID:19338387, PMID:1991028).
Reason: This is a key molecular function that distinguishes CelE from other CE2 family members. The cellulose-binding function is mediated through the active site of the CE2 domain, representing a novel dual-function in a single domain. Pull-down assays and AGE demonstrated binding to insoluble cellulose.
Supporting Evidence:
PMID:19338387
CtCE2 was previously characterized as a carbohydrate-binding module (CBM) by virtue of its cellulose-binding capacity and its ability to potentiate the cellulase activity of the linked CtCel5C catalytic module
PMID:19338387
Isothermal titration calorimetry (ITC) revealed that CtCE2 binds to cellooligosaccharides with a K
|
|
GO:0045493
xylan catabolic process
|
IDA
PMID:19338387 The active site of a carbohydrate esterase displays divergen... |
ACCEPT |
Summary: PMID:19338387 demonstrates that CelE (CtCE2 domain) deacetylates xylan, contributing to xylan catabolism by removing protective acetyl groups.
Reason: Direct experimental evidence shows the CE2 domain catalyzes deacetylation of acetylated birchwood xylan, contributing to xylan degradation.
Supporting Evidence:
PMID:19338387
All of these CE2 enzymes act as acetyl esterases, releasing acetate from activated artificial substrates such as 4-nitrophenyl acetate (4-NPAc; see Table 1) and, to different extents, the acetylated plant polysaccharides xylan and glucomannan
|
|
GO:0046555
acetylxylan esterase activity
|
IDA
PMID:19338387 The active site of a carbohydrate esterase displays divergen... |
ACCEPT |
Summary: PMID:19338387 provides extensive biochemical characterization of the acetylxylan esterase activity of the CE2 domain, including kinetic parameters (KM 2.7 mM, kcat 12 min-1 for acetylated birchwood xylan).
Reason: Strong experimental evidence supports this annotation. The CE2 domain was shown to deacetylate xylan with defined kinetic parameters.
Supporting Evidence:
PMID:19338387
All of these CE2 enzymes act as acetyl esterases, releasing acetate from activated artificial substrates such as 4-nitrophenyl acetate (4-NPAc; see Table 1) and, to different extents, the acetylated plant polysaccharides xylan and glucomannan
|
|
GO:2000884
glucomannan catabolic process
|
IDA
PMID:19338387 The active site of a carbohydrate esterase displays divergen... |
ACCEPT |
Summary: PMID:19338387 demonstrates that the CE2 domain preferentially deacetylates glucomannan over xylan, with KM of 0.019 mM showing very high affinity for this substrate.
Reason: Direct experimental evidence establishes CelE's role in glucomannan catabolism. The very low KM for glucomannan indicates this may be a preferred physiological substrate for the CE2 domain.
Supporting Evidence:
PMID:19338387
Based on their catalytic efficiencies, CtCE2 and CjCE2B exhibit a significant preference for acetylated glucomannan over xylan
|
|
GO:0043263
cellulosome
|
IDA
PMID:19338387 The active site of a carbohydrate esterase displays divergen... |
NEW |
Summary: CelE contains a type I dockerin domain that mediates its integration into the cellulosome complex. This localization is essential for its function in plant cell wall degradation.
Reason: The literature clearly establishes that CelE is a cellulosome component via its dockerin domain, but this cellular component annotation is missing from the current annotation set. This should be added as it represents a key aspect of the protein's localization and function.
Supporting Evidence:
PMID:19338387
The enzyme also contains a type I dockerin module that, by binding to cohesin modules in the scaffoldin protein, incorporates CtCel5C-CE2 into the multienzyme plant cell-wall-degrading complex known as the cellulosome
|
|
GO:1990311
type-I cohesin domain binding
|
IDA
PMID:19338387 The active site of a carbohydrate esterase displays divergen... |
NEW |
Summary: The dockerin domain of CelE binds to type-I cohesin domains in the scaffoldin protein, enabling integration into the cellulosome.
Reason: The type I dockerin domain of CelE binds to cohesin domains, which is essential for cellulosome assembly. This molecular function annotation would complete the annotation set.
Supporting Evidence:
PMID:19338387
The enzyme also contains a type I dockerin module that, by binding to cohesin modules in the scaffoldin protein, incorporates CtCel5C-CE2 into the multienzyme plant cell-wall-degrading complex
|
Q: What is the relative contribution of the cellulase vs esterase activities to plant cell wall degradation?
Q: Does the cellulose-binding function of the CE2 domain have regulatory significance beyond substrate targeting?
Q: Are there other CE2 family members that have gained cellulose-binding function through similar mechanisms?
Experiment: Quantify the enhancement of cellulase activity on natural plant cell wall substrates when CtCE2 cellulose binding is intact vs abolished
Hypothesis: The cellulose-binding function of CtCE2 significantly enhances cellulase activity on crystalline cellulose
Experiment: Determine whether CtCE2 cellulose binding affects cellulosome assembly or localization
Hypothesis: Cellulose binding by CtCE2 may help anchor the cellulosome to its substrate
Experiment: Characterize the deacetylation activity on native plant cell wall polysaccharides from different plant sources
Hypothesis: The preference for glucomannan may reflect the substrate composition of natural plant cell walls
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template_variables:
organism: ACET2
gene_id: P10477
gene_symbol: celE
uniprot_accession: P10477
protein_description: 'RecName: Full=Cellulase/esterase CelE {ECO:0000305}; AltName:
Full=CtCel5C-CE2 {ECO:0000303|PubMed:19338387}; Includes: RecName: Full=Cellulase
E {ECO:0000303|PubMed:3066698}; EC=3.2.1.4 {ECO:0000269|PubMed:1991028, ECO:0000269|PubMed:3066698};
AltName: Full=CtCel5C {ECO:0000303|PubMed:19338387}; AltName: Full=Endo-1,4-beta-glucanase
E {ECO:0000303|PubMed:3066698}; Short=EGE {ECO:0000303|PubMed:3066698}; Short=Endoglucanase
E {ECO:0000303|PubMed:3066698}; Includes: RecName: Full=Acetylxylan esterase /
glucomannan deacetylase {ECO:0000305|PubMed:19338387}; EC=3.1.1.- {ECO:0000269|PubMed:19338387};
EC=3.1.1.72 {ECO:0000269|PubMed:19338387}; AltName: Full=CtCE2 {ECO:0000303|PubMed:19338387};
Flags: Precursor;'
gene_info: Name=celE {ECO:0000303|PubMed:3066698}; OrderedLocusNames=Cthe_0797 {ECO:0000312|EMBL:ABN52032.1};
organism_full: Acetivibrio thermocellus (strain ATCC 27405 / DSM 1237 / JCM 9322
/ NBRC 103400 / NCIMB 10682 / NRRL B-4536 / VPI 7372) (Clostridium thermocellum).
protein_family: In the C-terminal section; belongs to the carbohydrate
protein_domains: CE2_N. (IPR040794); CtCE2-like_dom. (IPR037461); Dockerin_1_rpt.
(IPR002105); Dockerin_dom. (IPR016134); Dockerin_dom_sf. (IPR036439)
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BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.
DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'celE' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information
Please provide a comprehensive research report on the gene celE (gene ID: P10477, UniProt: P10477) in ACET2.
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.
Question: You are an expert researcher providing comprehensive, well-cited information.
Provide detailed information focusing on:
1. Key concepts and definitions with current understanding
2. Recent developments and latest research (prioritize 2023-2024 sources)
3. Current applications and real-world implementations
4. Expert opinions and analysis from authoritative sources
5. Relevant statistics and data from recent studies
Format as a comprehensive research report with proper citations. Include URLs and publication dates where available.
Always prioritize recent, authoritative sources and provide specific citations for all major claims.
BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.
DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'celE' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information
Please provide a comprehensive research report on the gene celE (gene ID: P10477, UniProt: P10477) in ACET2.
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.
Plan and verification
- Identity check: The target is celE encoding Endoglucanase E (also known as CelE; CtCel5C-CE2) from Clostridium thermocellum (syn. Acetivibrio thermocellus). Primary literature on Endoglucanase E (CelE) from C. thermocellum confirms gene/protein naming and association with the extracellular cellulosome. Early biochemical work mapped the catalytic N‑terminus and a distinct C‑terminal cellulose-binding region for Endoglucanase E, consistent with a multimodular, cellulosomal enzyme. Later studies characterized the appended CE2 esterase module (CtCE2) within the same protein, establishing bifunctionality alongside GH5 endoglucanase activity (montanier2009; gold2007; durrant1991; hazlewood1993) (montanier2009theactivesite pages 8-9, gold2007globalviewof pages 8-8, durrant1991thenoncatalyticcterminal pages 1-2, hazlewood1993genesequenceand pages 10-10).
Comprehensive research report
1) Key concepts and definitions with current understanding
- Protein and primary function: CelE (Endoglucanase E; UniProt P10477) is a cellulosomal, multimodular enzyme from C. thermocellum that combines an N‑terminal GH5 endo‑1,4‑β‑glucanase with a C‑terminal carbohydrate esterase family 2 (CE2) module. The GH5 domain hydrolyzes internal β‑1,4‑glucan linkages of cellulose/β‑glucans, while the CE2 domain catalyzes deacetylation reactions on plant polysaccharides and also provides noncatalytic cellulose binding that augments cellulase action (PLoS Biol, 2009-03-24; URL: https://doi.org/10.1371/journal.pbio.1000071). Proteomic analysis of native cellulosomes identified CelE as a bifunctional subunit with GH5 and CE2 domains (J Bacteriol, 2007-10; URL: https://doi.org/10.1128/jb.00882-07) (montanier2009theactivesite pages 8-9, gold2007globalviewof pages 8-8).
- Modular architecture: Early mapping of Endoglucanase E showed the N‑terminal catalytic region and a separate C‑terminal cellulose-binding domain; truncation constructs retained catalysis but lost cellulose affinity, highlighting distinct modules. This is consistent with later, more detailed modular annotations of GH5 and CE2 appended to a cellulosomal dockerin-bearing enzyme (Biochem J, 1991-01; URL: https://doi.org/10.1042/bj2730289; J Gen Microbiol, 1993-02; URL: https://doi.org/10.1099/00221287-139-2-307) (durrant1991thenoncatalyticcterminal pages 1-2, hazlewood1993genesequenceand pages 10-10).
- Cellulosome localization: Endoglucanase E is part of the extracellular cellulosome, a surface-anchored multi‑enzyme complex specialized for plant cell-wall deconstruction in C. thermocellum. Proteomics detected CelE in purified cellulosome preparations, supporting extracellular, complex-associated localization (J Bacteriol, 2007-10; URL: https://doi.org/10.1128/jb.00882-07) (gold2007globalviewof pages 8-8, durrant1991thenoncatalyticcterminal pages 1-2).
2) Recent developments and latest research (priority to 2023–2024 sources)
- Direct 2023–2024 sources specifically on C. thermocellum CelE/CtCel5C‑CE2 were not captured in the accessible evidence corpus. However, the modern mechanistic understanding of CelE’s CE2 module as both an esterase and a cellulose-binding enhancer derives from PLoS Biology (2009), which remains a definitive source on CtCE2’s multifunctionality within CelE (montanier2009theactivesite pages 8-9). Proteomic placement of CelE within the cellulosome and its regulation under substrates such as cellobiose was established in 2007 and remains relevant (gold2007globalviewof pages 8-8). Where 2023–2024 review statements on cellulosomes and CE2/GH5 roles are desired, additional targeted retrieval would be needed beyond the current evidence set.
3) Current applications and real-world implementations
- Biomass deconstruction and enzyme engineering: CelE’s bifunctional architecture exemplifies cellulosomal design that synergizes glycoside hydrolase activity with accessory deacetylation and substrate-binding, informing synthetic cellulosome assembly and enzyme cocktail optimization for industrial lignocellulose saccharification. The CtCE2 module’s unusual combination of catalysis and cellulose binding demonstrates a design principle for improving activity on recalcitrant substrates by embedding noncatalytic binding within the catalytic module’s site, potentially transferable to engineered biocatalysts for biomass valorization (PLoS Biol, 2009-03-24; URL: https://doi.org/10.1371/journal.pbio.1000071). Proteomic observations of CelE abundance under cellobiose growth conditions also provide cues for fermentation strategies and substrate-induced enzyme expression profiles relevant to bioprocess development (J Bacteriol, 2007-10; URL: https://doi.org/10.1128/jb.00882-07) (montanier2009theactivesite pages 8-9, gold2007globalviewof pages 8-8).
4) Expert opinions and analysis from authoritative sources
- Multifunctionality in CE2: Montanier et al. argue that the CtCE2 domain within CelE is an example of “gene sharing,” where a catalytic esterase active site also mediates noncatalytic cellulose binding via aromatic residue presentation, thereby boosting the appended GH5’s function on insoluble substrates without compromising esterase activity (PLoS Biol, 2009-03-24; URL: https://doi.org/10.1371/journal.pbio.1000071) (montanier2009theactivesite pages 8-9).
- Cellulosomal context and regulation: Quantitative proteomics by Gold and Martin provides a systems view of the C. thermocellum cellulosome, listing CelE as a bifunctional GH5+CE2 component whose relative abundance varies with growth substrate (e.g., cellobiose), reflecting coordinated regulation within the complex (J Bacteriol, 2007-10; URL: https://doi.org/10.1128/jb.00882-07) (gold2007globalviewof pages 8-8).
- Foundational mapping of CelE modularity: Durrant et al. and Hazlewood et al. established that Endoglucanase E contains separable catalytic and cellulose-binding regions, supporting the broader concept that cellulosomal enzymes bear modular architectures suited for extracellular polysaccharide deconstruction (Biochem J, 1991-01; J Gen Microbiol, 1993-02) (durrant1991thenoncatalyticcterminal pages 1-2, hazlewood1993genesequenceand pages 10-10).
5) Relevant statistics and data from recent studies
- Effects of CE2 aromatic residue mutations in CelE: Mutation of Trp‑790, Tyr‑665, or Trp‑746 in the CE2 module reduced cellulase activity on insoluble substrates by approximately 3–5‑fold, demonstrating the contribution of CE2-mediated cellulose binding to overall activity (PLoS Biol, 2009-03-24; URL: https://doi.org/10.1371/journal.pbio.1000071) (montanier2009theactivesite pages 8-9).
- CE2 catalytic assays and conditions: CtCE2 activity was quantified by hydrolysis of para‑nitrophenyl acetate (4‑NPAc) in defined buffer (e.g., 50 mM sodium phosphate, pH 7.0) and by acetate-release assays upon deacetylation of polysaccharide substrates; additional biophysical binding measurements included ITC and pull‑down with phosphoric acid-swollen cellulose (PLoS Biol, 2009-03-24; URL: https://doi.org/10.1371/journal.pbio.1000071) (montanier2009theactivesite pages 8-9).
- Modular mapping and activity tradeoffs in early work: Truncation analyses showed that the N‑terminal catalytic construct (EGEa) had about fourfold higher specific activity than the full-length Endoglucanase E but with reduced β‑glucan affinity, quantifying functional contributions of the C‑terminal binding region (Biochem J, 1991-01; URL: https://doi.org/10.1042/bj2730289) (durrant1991thenoncatalyticcterminal pages 1-2).
Mechanistic and pathway role
- Pathway context: CelE participates in extracellular cellulose and hemicellulose deconstruction within the C. thermocellum cellulosome. The GH5 domain cleaves internal β‑1,4‑glucan linkages in amorphous cellulose/β‑glucans, generating soluble oligosaccharides for downstream metabolism, while the CE2 module deacetylates noncellulosic plant polysaccharides (e.g., acetylated hemicelluloses), facilitating access for glycoside hydrolases; CE2 also binds cellulose to position CelE on insoluble substrates, enhancing catalytic efficiency on complex biomass (PLoS Biol, 2009-03-24; J Bacteriol, 2007-10) (montanier2009theactivesite pages 8-9, gold2007globalviewof pages 8-8).
Subcellular localization and complex membership
- CelE is secreted and incorporated into the cellulosome, as inferred from its identification in isolated cellulosome fractions and early biochemical characterization showing extracellular, cellulose-binding behavior characteristic of cellulosomal endoglucanases (J Bacteriol, 2007-10; Biochem J, 1991-01) (gold2007globalviewof pages 8-8, durrant1991thenoncatalyticcterminal pages 1-2).
Limitations and notes on recent literature
- Despite an explicit search for 2023–2024 sources specifically discussing CelE/CtCel5C‑CE2 in C. thermocellum, the present evidence set did not surface directly citable recent reviews focused on this protein. The core functional and structural understanding remains grounded in the definitive 2007–2009 literature cited above; additional targeted retrieval would be needed to incorporate any newer syntheses or updates.
Embedded evidence table
| Aspect | Key finding (1–2 sentences) | Organism / Protein | Method / Assay | Quant / Stats (if any) | Source (citation ID) | URL | Year |
|---|---|---|---:|---|---|---|---|
| Bifunctional architecture (GH5 + CE2) and cellulosomal association | CelE/CtCel5C-CE2 is a multimodular, bifunctional enzyme combining a GH5 catalytic module with a CE2 esterase module and is described as a cellulosomal (extracellular) subunit. | Clostridium thermocellum — CelE (CtCel5C-CE2, UniProt P10477) | Sequence/domain annotation and proteomics | N/A (domain architecture reported; abundance assessed by proteomics) | (gold2007globalviewof pages 8-8, montanier2009theactivesite pages 8-9) | https://doi.org/10.1128/jb.00882-07 ; https://doi.org/10.1371/journal.pbio.1000071 | 2007, 2009 |
| CE2 domain: dual esterase and cellulose‑binding functions enhancing cellulase activity | The CE2 module displays classical esterase (deacetylase) activity and a noncatalytic cellulose‑binding function that enhances the appended cellulase activity; mutations in aromatic residues in CE2 reduce cellulase activity ~3–5×. | Clostridium thermocellum — CtCE2 (C‑terminal of CtCel5C-CE2) | Site-directed mutagenesis; hydrolytic assays (4‑NPAc), acetate-release assays, ITC/binding and pull‑down with PASC; stopped‑flow pre‑steady‑state | Mutations (Trp-790, Tyr-665, Trp-746) reduce activity on insoluble substrates by ~3–5×; esterase and binding assays quantified in vitro | (montanier2009theactivesite pages 8-9) | https://doi.org/10.1371/journal.pbio.1000071 | 2009 |
| Early mapping: catalytic region vs C‑terminal cellulose‑binding region in Endoglucanase E | Endoglucanase E (product of celE) is ~780 aa; N‑terminal region contains the catalytic activity while a distinct C‑terminal cellulose‑binding domain (CBD) spans ~residues 432–671; truncation of the C‑terminus alters activity/affinity. | Clostridium thermocellum — Endoglucanase E (CelE / EGE) | Truncation constructs; binding to Avicel/biochemical assays; sequence analysis | N‑terminal construct (EGEa) showed ~4× higher specific activity than full‑length but lower β‑glucan affinity | (durrant1991thenoncatalyticcterminal pages 1-2, hazlewood1993genesequenceand pages 10-10) | https://doi.org/10.1042/bj2730289 ; https://doi.org/10.1099/00221287-139-2-307 | 1991, 1993 |
| Proteomic identification and regulation under cellobiose | Quantitative proteomics detected CelE in the native cellulosome and reported increased CelE abundance under cellobiose growth conditions, indicating regulated expression linked to substrate. | Clostridium thermocellum — CelE | Quantitative proteomic analysis of isolated cellulosomes from different growth substrates | Increase in CelE abundance under cellobiose reported (fold‑change not specified in excerpt) | (gold2007globalviewof pages 8-8) | https://doi.org/10.1128/jb.00882-07 | 2007 |
| Evidence for extracellular / cellulosome localization of endoglucanases (including CelE family) | Endoglucanase E and related cellulases are secreted/extracellular and are components of the cellulosome (cell‑surface multi‑enzyme complex), with CBDs mediating tight binding to cellulose. | Clostridium thermocellum — Endoglucanases (CelE family) | Biochemical fractionation/isolation of cellulosome, binding assays, proteomics | Mature enzyme size and extracellular association reported; CBD mediates Avicel binding | (durrant1991thenoncatalyticcterminal pages 1-2, gold2007globalviewof pages 8-8) | https://doi.org/10.1042/bj2730289 ; https://doi.org/10.1128/jb.00882-07 | 1991, 2007 |
| Kinetic / activity assay details reported for CE2 | CE2 activity measured by hydrolysis of model esterase substrates (e.g., 4‑NPAc) and acetate‑release (deacetylation) assays; stopped‑flow and pre‑steady‑state experiments and binding assays were used to dissect catalytic vs binding roles. | Clostridium thermocellum — CtCE2 (part of CtCel5C-CE2) | 4‑NPAc hydrolysis assays, acetate release (Megazyme kit), stopped‑flow pre‑steady‑state with cellohexaose, ITC, pull‑down | Assay conditions and comparative activities reported; mutational effects on activity (3–5× reductions) documented | (montanier2009theactivesite pages 8-9) | https://doi.org/10.1371/journal.pbio.1000071 | 2009 |
Table: Concise literature evidence for CelE (CtCel5C‑CE2, UniProt P10477) summarizing domain architecture, CE2 multifunctionality, localization to the cellulosome, proteomic detection, and key assay/quantitative findings from primary sources.
References (with URLs and publication dates)
- Montanier C et al. The active site of a carbohydrate esterase displays divergent catalytic and noncatalytic binding functions. PLoS Biology. 2009-03-24. URL: https://doi.org/10.1371/journal.pbio.1000071 (montanier2009theactivesite pages 8-9)
- Gold ND, Martin VJJ. Global view of the Clostridium thermocellum cellulosome revealed by quantitative proteomic analysis. Journal of Bacteriology. 2007-10. URL: https://doi.org/10.1128/jb.00882-07 (gold2007globalviewof pages 8-8)
- Durrant AJ et al. The non‑catalytic C‑terminal region of endoglucanase E from Clostridium thermocellum contains a cellulose‑binding domain. Biochemical Journal. 1991-01. URL: https://doi.org/10.1042/bj2730289 (durrant1991thenoncatalyticcterminal pages 1-2)
- Hazlewood GP et al. Gene sequence and properties of CelI, a family E endoglucanase from Clostridium thermocellum. Journal of General Microbiology. 1993-02. URL: https://doi.org/10.1099/00221287-139-2-307 (hazlewood1993genesequenceand pages 10-10)
References
(montanier2009theactivesite pages 8-9): Cedric Montanier, Victoria A Money, Virginia M. R Pires, James E Flint, Benedita A Pinheiro, Arun Goyal, José A. M Prates, Atsushi Izumi, Henrik Stålbrand, Carl Morland, Alan Cartmell, Katarina Kolenova, Evangelos Topakas, Eleanor J Dodson, David N Bolam, Gideon J Davies, Carlos M. G. A Fontes, and Harry J Gilbert. The active site of a carbohydrate esterase displays divergent catalytic and noncatalytic binding functions. PLoS Biology, 7:e1000071, Mar 2009. URL: https://doi.org/10.1371/journal.pbio.1000071, doi:10.1371/journal.pbio.1000071. This article has 83 citations and is from a highest quality peer-reviewed journal.
(gold2007globalviewof pages 8-8): Nicholas D. Gold and Vincent J. J. Martin. Global view of the clostridium thermocellum cellulosome revealed by quantitative proteomic analysis. Journal of Bacteriology, 189:6787-6795, Oct 2007. URL: https://doi.org/10.1128/jb.00882-07, doi:10.1128/jb.00882-07. This article has 271 citations and is from a peer-reviewed journal.
(durrant1991thenoncatalyticcterminal pages 1-2): Alastair J. Durrant, Judith Hall, Geoffrey P. HAZLEWOODt, and H. Gilbert. The non-catalytic c-terminal region of endoglucanase e from clostridium thermocellum contains a cellulose-binding domain. The Biochemical journal, 273(Pt 2):289-93, Jan 1991. URL: https://doi.org/10.1042/bj2730289, doi:10.1042/bj2730289. This article has 63 citations.
(hazlewood1993genesequenceand pages 10-10): G. P. Hazlewood, K. Davidson, J. I. Laurie, N. S. Huskisson, and H. J. Gilbert. Gene sequence and properties of cell, a family e endoglucanase from clostridium thermocellum. Journal of General Microbiology, 139:307-316, Feb 1993. URL: https://doi.org/10.1099/00221287-139-2-307, doi:10.1099/00221287-139-2-307. This article has 52 citations.
id: P10477
gene_symbol: celE
aliases:
- CelE
- Endoglucanase E
- EGE
product_type: PROTEIN
status: DRAFT
taxon:
id: NCBITaxon:203119
label: Acetivibrio thermocellus (strain ATCC 27405 / DSM 1237 / JCM 9322 / NBRC
103400 / NCIMB 10682 / NRRL B-4536 / VPI 7372)
description: >
CelE (CtCel5C-CE2) is a multifunctional enzyme involved in plant cell wall degradation.
It contains an N-terminal GH5 cellulase domain (CtCel5C), a central type I dockerin module
for cellulosome integration, and a C-terminal CE2 esterase domain (CtCE2). The GH5 domain
displays endo-1,4-beta-glucanase activity against cellulose, beta-glucan, and CMC. The CE2 domain
exhibits both acetylxylan esterase and glucomannan deacetylase activities, with strong preference
for glucomannan. Uniquely, the CE2 domain also functions as a cellulose-binding module through
its catalytic site region, potentiating the cellulase activity of the appended GH5 domain on
recalcitrant substrates.
existing_annotations:
- term:
id: GO:0000272
label: polysaccharide catabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >
This broad biological process annotation is supported by the established functions of CelE
in degrading cellulose, xylan, and glucomannan - all plant cell wall polysaccharides
(PMID:19338387, PMID:3066698).
action: ACCEPT
reason: >
CelE functions in the catabolism of multiple polysaccharides including cellulose, xylan,
and glucomannan. This general term correctly captures the enzyme's role in polysaccharide
breakdown, though more specific terms (cellulose catabolic process, xylan catabolic process,
glucomannan catabolic process) provide greater specificity and are also annotated.
supported_by:
- reference_id: PMID:19338387
supporting_text: "CtCE2 catalyses deacetylation of noncellulosic plant structural polysaccharides to deprotect these substrates for attack by other enzymes"
- reference_id: PMID:3066698
supporting_text: "The complete nucleotide sequence of the Clostridium thermocellum celE gene, coding for an endo-beta-1,4-glucanase (endoglucanase E; EGE) with xylan-hydrolysing activity has been determined."
- reference_id: file:ACET2/P10477/P10477-deep-research-falcon.md
supporting_text: "CelE is a bifunctional enzyme with both cellulase and esterase domains"
- term:
id: GO:0003824
label: catalytic activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >
This is a very general molecular function term that is true but uninformative.
CelE has well-characterized specific catalytic activities including cellulase (EC 3.2.1.4)
and acetylxylan esterase (EC 3.1.1.72) activities.
action: KEEP_AS_NON_CORE
reason: >
While technically correct, this term is too general to be informative. The specific
catalytic activities (cellulase activity GO:0008810, acetylxylan esterase activity GO:0046555)
are far more useful annotations. This annotation can be retained as a parent term but
should not be considered a core annotation.
- term:
id: GO:0004553
label: hydrolase activity, hydrolyzing O-glycosyl compounds
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >
This annotation correctly captures the glycoside hydrolase activity of the GH5 domain.
The enzyme hydrolyzes beta-1,4-glucosidic linkages in cellulose and beta-glucan (PMID:3066698, PMID:1991028).
action: ACCEPT
reason: >
The GH5 cellulase domain of CelE catalyzes hydrolysis of O-glycosyl bonds in cellulose.
This is an accurate parent term for the more specific cellulase activity.
supported_by:
- reference_id: PMID:3066698
supporting_text: "coding for an endo-beta-1,4-glucanase (endoglucanase E; EGE)"
- term:
id: GO:0005576
label: extracellular region
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: >
CelE is a secreted protein that functions as part of the extracellular cellulosome complex.
The protein has a signal peptide (residues 1-34) and integrates into the cellulosome via
its dockerin domain.
action: ACCEPT
reason: >
The UniProt record indicates the protein is secreted (signal peptide residues 1-34),
and the protein functions in the extracellular cellulosome complex. The dockerin domain
mediates integration into this extracellular multi-enzyme complex.
supported_by:
- reference_id: PMID:19338387
supporting_text: "The enzyme also contains a type I dockerin module that, by binding to cohesin modules in the scaffoldin protein, incorporates CtCel5C-CE2 into the multienzyme plant cell-wall-degrading complex known as the cellulosome"
- term:
id: GO:0005975
label: carbohydrate metabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >
This very broad biological process term is accurate but provides minimal specificity.
The enzyme is involved in carbohydrate catabolism, specifically of polysaccharides.
action: KEEP_AS_NON_CORE
reason: >
While technically correct, this is a very high-level term. The more specific terms
(cellulose catabolic process, xylan catabolic process, glucomannan catabolic process)
provide much better functional annotation.
- term:
id: GO:0008810
label: cellulase activity
evidence_type: IEA
original_reference_id: GO_REF:0000003
review:
summary: >
Cellulase activity is a core function of CelE, demonstrated through biochemical assays
showing activity against CMC and barley beta-glucan (PMID:3066698, PMID:1991028).
This activity is localized to the N-terminal GH5 domain (CtCel5C).
action: ACCEPT
reason: >
This is a core molecular function of CelE. The enzyme has EC 3.2.1.4 activity confirmed
by direct experimental evidence. The GH5 domain catalyzes endohydrolysis of (1->4)-beta-D-glucosidic
linkages in cellulose.
supported_by:
- reference_id: PMID:3066698
supporting_text: "coding for an endo-beta-1,4-glucanase (endoglucanase E; EGE)"
- term:
id: GO:0016787
label: hydrolase activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >
CelE is a hydrolase with both glycosidase and esterase activities. This broad term
is accurate but not specific.
action: KEEP_AS_NON_CORE
reason: >
This is a parent term that is technically correct but uninformative. The specific
hydrolase activities (cellulase, acetylxylan esterase) are better annotations.
- term:
id: GO:0016788
label: hydrolase activity, acting on ester bonds
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >
The CE2 domain of CelE has well-characterized esterase activity, catalyzing deacetylation
of xylan and glucomannan (PMID:19338387).
action: ACCEPT
reason: >
This correctly captures the esterase activity of the CE2 domain. The enzyme hydrolyzes
acetyl ester bonds in acetylated polysaccharides. More specific terms (acetylxylan esterase
activity) provide additional detail.
supported_by:
- reference_id: PMID:19338387
supporting_text: "All of these CE2 enzymes act as acetyl esterases, releasing acetate from activated artificial substrates such as 4-nitrophenyl acetate (4-NPAc; see Table 1) and, to different extents, the acetylated plant polysaccharides xylan and glucomannan"
- term:
id: GO:0016798
label: hydrolase activity, acting on glycosyl bonds
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >
This annotation correctly captures the glycoside hydrolase activity of the GH5 domain,
which cleaves beta-1,4-glucosidic bonds in cellulose.
action: ACCEPT
reason: >
The GH5 domain of CelE is a glycoside hydrolase that cleaves glycosyl bonds. This
is a parent term for the more specific cellulase activity annotation.
supported_by:
- reference_id: PMID:3066698
supporting_text: "coding for an endo-beta-1,4-glucanase"
- term:
id: GO:0030245
label: cellulose catabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >
CelE participates in cellulose degradation through its GH5 cellulase domain, which
hydrolyzes beta-1,4-glucosidic linkages in cellulose. The CE2 domain further enhances
this activity by binding to cellulose and bringing the enzyme into contact with its
substrate (PMID:19338387, PMID:1991028).
action: ACCEPT
reason: >
This is a core biological process annotation. CelE is a cellulosome component that
directly participates in cellulose catabolism through its cellulase activity and
cellulose-binding function.
supported_by:
- reference_id: PMID:19338387
supporting_text: "it also acts as a cellulose-binding domain, which promotes the activity of the appended cellulase on recalcitrant substrates"
- term:
id: GO:0046555
label: acetylxylan esterase activity
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >
The CE2 domain of CelE has acetylxylan esterase activity (EC 3.1.1.72), catalyzing
deacetylation of xylan (PMID:19338387). Kinetic parameters show KM of 2.7 mM and
kcat of 12 min-1 for acetylated birchwood xylan.
action: ACCEPT
reason: >
This is a core molecular function of the CE2 domain. The enzyme catalyzes deacetylation
of xylan, removing acetyl groups that protect the xylan backbone from degradation by
other enzymes.
supported_by:
- reference_id: PMID:19338387
supporting_text: "CtCE2 and CjCE2B exhibit a significant preference for acetylated glucomannan over xylan"
- term:
id: GO:0046872
label: metal ion binding
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >
The dockerin domain of CelE contains calcium-binding sites that are essential for
its function in binding to cohesin domains of the scaffoldin protein. Multiple
calcium-binding residues are annotated in the UniProt record (residues 415-462).
action: MODIFY
reason: >
While this annotation is technically correct, it would be more informative to use
the more specific term GO:0005509 (calcium ion binding), as the metal binding is
specifically to calcium ions in the dockerin domain.
proposed_replacement_terms:
- id: GO:0005509
label: calcium ion binding
- term:
id: GO:0052689
label: carboxylic ester hydrolase activity
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >
The CE2 domain hydrolyzes carboxylic esters (acetyl groups) from polysaccharides.
This is consistent with its acetylxylan esterase and glucomannan deacetylase activities.
action: ACCEPT
reason: >
This is an accurate parent term for the esterase activity. The CE2 domain catalyzes
hydrolysis of acetyl ester bonds, releasing acetate from polysaccharide substrates.
supported_by:
- reference_id: PMID:19338387
supporting_text: "The esterases appear specific for acetyl groups"
- term:
id: GO:2000884
label: glucomannan catabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000117
review:
summary: >
CelE participates in glucomannan catabolism through deacetylation of acetylated
glucomannan by its CE2 domain. The enzyme shows preference for glucomannan over
xylan, with KM of 0.019 mM (PMID:19338387).
action: ACCEPT
reason: >
This is a core biological process annotation. The CE2 domain deacetylates glucomannan,
removing acetyl groups that protect the polysaccharide from degradation. The very
low KM indicates high affinity for this substrate.
supported_by:
- reference_id: PMID:19338387
supporting_text: "CtCE2 and CjCE2B exhibit a significant preference for acetylated glucomannan over xylan"
- term:
id: GO:0045493
label: xylan catabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >
CelE participates in xylan catabolism through both its xylanase activity (noted in
PMID:3066698) and its acetylxylan esterase activity that deacetylates xylan to make
it accessible to other enzymes (PMID:19338387).
action: ACCEPT
reason: >
This is a core biological process annotation. The original characterization noted
xylan-hydrolyzing activity, and the CE2 domain deacetylates xylan, contributing to
xylan degradation.
supported_by:
- reference_id: PMID:3066698
supporting_text: "an endo-beta-1,4-glucanase (endoglucanase E; EGE) with xylan-hydrolysing activity"
- reference_id: PMID:19338387
supporting_text: "CtCE2 catalyses deacetylation of noncellulosic plant structural polysaccharides to deprotect these substrates for attack by other enzymes"
- term:
id: GO:0008810
label: cellulase activity
evidence_type: IDA
original_reference_id: PMID:3066698
review:
summary: >
Direct experimental evidence from the original characterization of CelE demonstrates
cellulase activity against cellulose substrates (PMID:3066698).
action: ACCEPT
reason: >
This IDA annotation is strongly supported by the original biochemical characterization
of CelE as an endoglucanase. This is a core molecular function.
supported_by:
- reference_id: PMID:3066698
supporting_text: "coding for an endo-beta-1,4-glucanase (endoglucanase E; EGE)"
- term:
id: GO:0030245
label: cellulose catabolic process
evidence_type: IDA
original_reference_id: PMID:3066698
review:
summary: >
The original characterization established CelE's role in cellulose degradation.
action: ACCEPT
reason: >
This IDA annotation is appropriate based on the biochemical evidence for cellulase
activity and the enzyme's role in the cellulosome complex.
supported_by:
- reference_id: PMID:3066698
supporting_text: "coding for an endo-beta-1,4-glucanase"
- term:
id: GO:0030248
label: cellulose binding
evidence_type: IDA
original_reference_id: PMID:19338387
review:
summary: >
The CE2 domain of CelE binds cellulose through a unique mechanism involving its
catalytic site region. ITC measurements show KD of 33 uM for cellohexaose. This
binding potentiates the activity of the appended cellulase domain on recalcitrant
substrates (PMID:19338387, PMID:1991028).
action: ACCEPT
reason: >
This is a key molecular function that distinguishes CelE from other CE2 family
members. The cellulose-binding function is mediated through the active site of
the CE2 domain, representing a novel dual-function in a single domain. Pull-down
assays and AGE demonstrated binding to insoluble cellulose.
supported_by:
- reference_id: PMID:19338387
supporting_text: "CtCE2 was previously characterized as a carbohydrate-binding module (CBM) by virtue of its cellulose-binding capacity and its ability to potentiate the cellulase activity of the linked CtCel5C catalytic module"
- reference_id: PMID:19338387
supporting_text: "Isothermal titration calorimetry (ITC) revealed that CtCE2 binds to cellooligosaccharides with a K"
- term:
id: GO:0045493
label: xylan catabolic process
evidence_type: IDA
original_reference_id: PMID:19338387
review:
summary: >
PMID:19338387 demonstrates that CelE (CtCE2 domain) deacetylates xylan, contributing
to xylan catabolism by removing protective acetyl groups.
action: ACCEPT
reason: >
Direct experimental evidence shows the CE2 domain catalyzes deacetylation of
acetylated birchwood xylan, contributing to xylan degradation.
supported_by:
- reference_id: PMID:19338387
supporting_text: "All of these CE2 enzymes act as acetyl esterases, releasing acetate from activated artificial substrates such as 4-nitrophenyl acetate (4-NPAc; see Table 1) and, to different extents, the acetylated plant polysaccharides xylan and glucomannan"
- term:
id: GO:0046555
label: acetylxylan esterase activity
evidence_type: IDA
original_reference_id: PMID:19338387
review:
summary: >
PMID:19338387 provides extensive biochemical characterization of the acetylxylan
esterase activity of the CE2 domain, including kinetic parameters (KM 2.7 mM,
kcat 12 min-1 for acetylated birchwood xylan).
action: ACCEPT
reason: >
Strong experimental evidence supports this annotation. The CE2 domain was shown
to deacetylate xylan with defined kinetic parameters.
supported_by:
- reference_id: PMID:19338387
supporting_text: "All of these CE2 enzymes act as acetyl esterases, releasing acetate from activated artificial substrates such as 4-nitrophenyl acetate (4-NPAc; see Table 1) and, to different extents, the acetylated plant polysaccharides xylan and glucomannan"
- term:
id: GO:2000884
label: glucomannan catabolic process
evidence_type: IDA
original_reference_id: PMID:19338387
review:
summary: >
PMID:19338387 demonstrates that the CE2 domain preferentially deacetylates glucomannan
over xylan, with KM of 0.019 mM showing very high affinity for this substrate.
action: ACCEPT
reason: >
Direct experimental evidence establishes CelE's role in glucomannan catabolism.
The very low KM for glucomannan indicates this may be a preferred physiological
substrate for the CE2 domain.
supported_by:
- reference_id: PMID:19338387
supporting_text: "Based on their catalytic efficiencies, CtCE2 and CjCE2B exhibit a significant preference for acetylated glucomannan over xylan"
# Additional annotation that should be added based on the evidence
- term:
id: GO:0043263
label: cellulosome
evidence_type: IDA
original_reference_id: PMID:19338387
review:
summary: >
CelE contains a type I dockerin domain that mediates its integration into the
cellulosome complex. This localization is essential for its function in plant
cell wall degradation.
action: NEW
reason: >
The literature clearly establishes that CelE is a cellulosome component via its
dockerin domain, but this cellular component annotation is missing from the current
annotation set. This should be added as it represents a key aspect of the protein's
localization and function.
supported_by:
- reference_id: PMID:19338387
supporting_text: "The enzyme also contains a type I dockerin module that, by binding to cohesin modules in the scaffoldin protein, incorporates CtCel5C-CE2 into the multienzyme plant cell-wall-degrading complex known as the cellulosome"
- term:
id: GO:1990311
label: type-I cohesin domain binding
evidence_type: IDA
original_reference_id: PMID:19338387
review:
summary: >
The dockerin domain of CelE binds to type-I cohesin domains in the scaffoldin
protein, enabling integration into the cellulosome.
action: NEW
reason: >
The type I dockerin domain of CelE binds to cohesin domains, which is essential
for cellulosome assembly. This molecular function annotation would complete the
annotation set.
supported_by:
- reference_id: PMID:19338387
supporting_text: "The enzyme also contains a type I dockerin module that, by binding to cohesin modules in the scaffoldin protein, incorporates CtCel5C-CE2 into the multienzyme plant cell-wall-degrading complex"
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO terms
findings: []
- id: GO_REF:0000003
title: Gene Ontology annotation based on Enzyme Commission mapping
findings: []
- id: GO_REF:0000043
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
findings: []
- id: GO_REF:0000044
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
vocabulary mapping, accompanied by conservative changes to GO terms applied by
UniProt
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:19338387
title: The active site of a carbohydrate esterase displays divergent catalytic and
noncatalytic binding functions.
findings:
- statement: The CE2 domain (CtCE2) displays dual function with acetylxylan esterase/glucomannan deacetylase activity and cellulose-binding function, uniquely mediated through the same active site region.
supporting_text: "the CtCE2 domain displays divergent catalytic esterase and noncatalytic carbohydrate binding functions"
- statement: CtCE2 binds cellooligosaccharides with high affinity.
supporting_text: "Isothermal titration calorimetry (ITC) revealed that CtCE2 binds to cellooligosaccharides with a K"
- statement: The enzyme shows strong preference for glucomannan over xylan.
supporting_text: "Based on their catalytic efficiencies, CtCE2 and CjCE2B exhibit a significant preference for acetylated glucomannan over xylan"
- statement: Cellulose binding inhibits esterase activity, demonstrating the overlap of catalytic and binding functions.
supporting_text: "cellohexaose and beta-glucan binding inhibit the esterase activity of the wild-type CtCE2 enzyme"
- statement: The type I dockerin domain mediates incorporation into the cellulosome.
supporting_text: "The enzyme also contains a type I dockerin module that, by binding to cohesin modules in the scaffoldin protein, incorporates CtCel5C-CE2 into the multienzyme plant cell-wall-degrading complex known as the cellulosome"
- id: PMID:3066698
title: Conserved reiterated domains in Clostridium thermocellum endoglucanases are
not essential for catalytic activity.
findings:
- statement: Original characterization of CelE as an endo-beta-1,4-glucanase with xylan-hydrolysing activity.
supporting_text: "The complete nucleotide sequence of the Clostridium thermocellum celE gene, coding for an endo-beta-1,4-glucanase (endoglucanase E; EGE) with xylan-hydrolysing activity has been determined"
- statement: Identified the structural gene and confirmed N-terminal sequence of the purified protein.
supporting_text: "The nucleotide sequence obtained has been confirmed by comparing the predicted amino acid sequence with that derived by N-terminal amino acid sequencing of the purified protein"
- id: PMID:1991028
title: The non-catalytic C-terminal region of endoglucanase E from Clostridium
thermocellum contains a cellulose-binding domain.
findings:
- statement: Demonstrated endoglucanase activity against CMC and barley beta-glucan.
supporting_text: "Mature endoglucanase E (EGE) from Clostridium thermocellum consists of 780 amino acid residues and has an Mr of 84,016. The N-terminal 334 amino acids comprise a functional catalytic domain"
- statement: Identified the C-terminal cellulose-binding function.
supporting_text: "It is concluded that EGE contains a cellulose-binding domain, located between residues 432 and 671, that is distinct from the active site"
core_functions:
- description: >
The N-terminal GH5 domain (CtCel5C) catalyzes endohydrolysis of (1->4)-beta-D-glucosidic
linkages in cellulose, with demonstrated activity against CMC and barley beta-glucan
(PMID:3066698, PMID:1991028).
molecular_function:
id: GO:0008810
label: cellulase activity
directly_involved_in:
- id: GO:0030245
label: cellulose catabolic process
locations:
- id: GO:0005576
label: extracellular region
- description: >
The C-terminal CE2 domain catalyzes deacetylation of acetylated polysaccharides,
with strong preference for glucomannan (KM 0.019 mM) over xylan (KM 2.7 mM).
This activity removes protective acetyl groups to expose substrates for attack
by other enzymes (PMID:19338387).
molecular_function:
id: GO:0046555
label: acetylxylan esterase activity
directly_involved_in:
- id: GO:0045493
label: xylan catabolic process
- id: GO:2000884
label: glucomannan catabolic process
locations:
- id: GO:0005576
label: extracellular region
- description: >
Uniquely among CE2 family members, the CtCE2 domain binds cellulose through its
active site region (KD 33 uM for cellohexaose). This binding potentiates the
cellulase activity of the appended GH5 domain on recalcitrant substrates (PMID:19338387).
molecular_function:
id: GO:0030248
label: cellulose binding
directly_involved_in:
- id: GO:0030245
label: cellulose catabolic process
locations:
- id: GO:0005576
label: extracellular region
- description: >
Contains a type I dockerin domain that binds to cohesin modules in the scaffoldin
protein, integrating CelE into the extracellular cellulosome complex for efficient
plant cell wall degradation (PMID:19338387).
molecular_function:
id: GO:1990311
label: type-I cohesin domain binding
locations:
- id: GO:0043263
label: cellulosome
proposed_new_terms: []
suggested_questions:
- question: What is the relative contribution of the cellulase vs esterase activities to plant cell wall degradation?
- question: Does the cellulose-binding function of the CE2 domain have regulatory significance beyond substrate targeting?
- question: Are there other CE2 family members that have gained cellulose-binding function through similar mechanisms?
suggested_experiments:
- description: Quantify the enhancement of cellulase activity on natural plant cell wall substrates when CtCE2 cellulose binding is intact vs abolished
hypothesis: The cellulose-binding function of CtCE2 significantly enhances cellulase activity on crystalline cellulose
- description: Determine whether CtCE2 cellulose binding affects cellulosome assembly or localization
hypothesis: Cellulose binding by CtCE2 may help anchor the cellulosome to its substrate
- description: Characterize the deacetylation activity on native plant cell wall polysaccharides from different plant sources
hypothesis: The preference for glucomannan may reflect the substrate composition of natural plant cell walls