CRH1 (Congo Red Hypersensitive protein 1) encodes a GPI-anchored cell wall transglycosylase of the GH16 family that cross-links chitin to both beta(1-3)- and beta(1-6)-glucan in the S. cerevisiae cell wall. The enzyme uses a retaining double-displacement mechanism: it cleaves a chitin donor chain and transfers it to glucan acceptors, thereby integrating chitin into the glucan network. CRH1 has a secondary weak endochitinase activity (EC 3.2.1.14) but its primary biological role is as a chitin transglycosylase (EC 2.4.-.-). The protein is GPI-anchored at the cell surface and concentrated at chitin-rich areas including the incipient bud site, septum, and bud scars. CRH1 acts redundantly with its paralog CRH2/UTR2; the double mutant completely lacks chitin-glucan cross-links and shows strong sensitivity to Congo Red and Calcofluor White. CRH1 expression is cell-cycle regulated, induced during sporulation, and upregulated by the cell wall integrity pathway (MPK1/RLM1) in response to heat stress and cell wall damage. Present at approximately 44,000 wall-bound copies per cell in log phase.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0005576
extracellular region
|
IBA
GO_REF:0000033 |
KEEP AS NON CORE |
Summary: IBA annotation from phylogenetic inference. CRH1 is a GPI-anchored cell wall protein that is secreted and covalently attached to the outer cell wall. While "extracellular region" is not wrong for a secreted protein, the more specific and accurate term is "fungal-type cell wall" (GO:0009277), which is already annotated with direct experimental evidence (IDA). This IBA adds little information beyond the existing IDA annotations.
Reason: Technically correct but too broad. CRH1 is a GPI-CWP covalently incorporated into the cell wall, not a freely secreted extracellular protein. The IDA annotation to fungal-type cell wall is more informative.
|
|
GO:0006030
chitin metabolic process
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: IBA annotation from phylogenetic inference. CRH1 is directly involved in chitin metabolic process as a chitin transglycosylase that transfers chitin chains to glucan acceptors. This is consistent with IMP and IGI evidence from PMID:18694928.
Reason: Correct and supported by direct experimental evidence. CRH1 transfers chitin to glucan, which is a chitin metabolic process.
|
|
GO:0031505
fungal-type cell wall organization
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: IBA annotation from phylogenetic inference. CRH1 is a key enzyme in fungal cell wall organization, cross-linking chitin to the glucan network. This is consistent with IMP and IGI evidence from PMID:18694928.
Reason: Correct. CRH1 cross-links chitin to glucan, which is an essential step in cell wall organization. Well-supported by multiple lines of evidence.
|
|
GO:0009277
fungal-type cell wall
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: IBA annotation from phylogenetic inference for cell wall localization. CRH1 is a GPI-CWP covalently attached to the cell wall, confirmed by mass spectrometry (PMID:15781460) and GFP localization (PMID:10757808). Consistent with IDA evidence.
Reason: Correct. CRH1 is covalently linked to the cell wall via its GPI anchor remnant. Multiple IDA annotations confirm this.
|
|
GO:0016757
glycosyltransferase activity
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: IBA annotation from phylogenetic inference. CRH1 is a chitin transglycosylase that transfers chitin chains to glucan acceptors, which is a glycosyltransferase activity. Supported by IDA evidence from PMID:23919454 and IMP/IGI from PMID:18694928.
Reason: Correct. Transglycosylase activity is a form of glycosyltransferase activity. This is the core molecular function of CRH1.
|
|
GO:0004553
hydrolase activity, hydrolyzing O-glycosyl compounds
|
IEA
GO_REF:0000002 |
KEEP AS NON CORE |
Summary: IEA from InterPro mapping (IPR000757 Beta-glucanase-like domain). CRH1 does have weak endochitinase activity (EC 3.2.1.14) as demonstrated by Mazan et al. (2013), so the annotation is not incorrect. However, the primary function is transglycosylase activity, not hydrolase activity. The hydrolytic activity is secondary and weak.
Reason: Technically correct -- CRH1 has documented weak endochitinase activity (PMID:23919454) -- but the primary evolved function is transglycosylation, not hydrolysis. This InterPro-based annotation reflects the ancestral GH16 hydrolase function rather than the derived transglycosylase specialization.
Supporting Evidence:
file:yeast/CRH1/CRH1-deep-research-bioreason-sft.md
[BioReason identifies the GH16 catalytic core as executing a retaining double-displacement reaction, consistent with the transglycosylase being the primary function rather than simple hydrolysis]
|
|
GO:0005975
carbohydrate metabolic process
|
IEA
GO_REF:0000002 |
KEEP AS NON CORE |
Summary: IEA from InterPro mapping. CRH1 is indeed involved in carbohydrate metabolism (chitin and glucan processing). This is correct but very broad -- the more specific term "chitin metabolic process" (GO:0006030) is already annotated.
Reason: Correct but very broad. Subsumed by the more specific GO:0006030 (chitin metabolic process) which is already annotated with experimental evidence.
|
|
GO:0008843
endochitinase activity
|
IEA
GO_REF:0000003 |
KEEP AS NON CORE |
Summary: IEA from EC number mapping (EC 3.2.1.14). Mazan et al. (2013) demonstrated weak endochitinase activity for heterologously expressed CRH1. The endo:exo chitinase ratio was approximately 4-fold higher in Crh1 than Crh2. However, the chitinase activity is secondary to the primary transglycosylase function.
Reason: Correct. CRH1 has documented endochitinase activity (PMID:23919454), but this is a secondary activity. The primary molecular function is chitin transglycosylase activity.
Supporting Evidence:
PMID:23919454
Both proteins exhibited a weak chitinolytic activity in different assays whereby the ratio of endo- compared with exo-chitinase activity was approximately 4-fold higher in Crh1 than in Crh2
|
|
GO:0009277
fungal-type cell wall
|
IEA
GO_REF:0000117 |
ACCEPT |
Summary: IEA from ARBA machine learning model. Correct -- CRH1 is covalently linked to the fungal-type cell wall. Redundant with IDA annotations from PMID:10757808 and PMID:15781460.
Reason: Correct and consistent with multiple lines of direct experimental evidence.
|
|
GO:0016020
membrane
|
IEA
GO_REF:0000044 |
KEEP AS NON CORE |
Summary: IEA from UniProtKB subcellular location mapping. CRH1 is GPI-anchored to the outer leaflet of the plasma membrane before being transferred to the cell wall. The annotation is technically correct but imprecise. CRH1 is primarily a cell wall protein, not a membrane protein in the traditional sense. The GPI anchor transiently associates it with the membrane during transport.
Reason: Technically correct (GPI-anchored to membrane) but misleading for CRH1, which is primarily a covalently-linked cell wall protein. The GPI anchor is processed during transfer to the cell wall.
|
|
GO:0016798
hydrolase activity, acting on glycosyl bonds
|
IEA
GO_REF:0000002 |
KEEP AS NON CORE |
Summary: IEA from InterPro mapping (IPR017168 CRH-like family). CRH1 has weak endochitinase activity, so hydrolysis of glycosyl bonds is technically correct. However, this is a parent term of endochitinase activity (GO:0008843) which is already annotated, and the primary function is transglycosylation rather than hydrolysis.
Reason: Correct but broad and redundant. The more specific endochitinase activity (GO:0008843) is already annotated. The primary function is transglycosylase, not hydrolase.
|
|
GO:0031505
fungal-type cell wall organization
|
IEA
GO_REF:0000117 |
ACCEPT |
Summary: IEA from ARBA machine learning model. Correct -- CRH1 is essential for cell wall organization through chitin-glucan cross-linking. Consistent with IMP/IGI evidence.
Reason: Correct and consistent with experimental evidence from PMID:18694928.
|
|
GO:0071555
cell wall organization
|
IEA
GO_REF:0000002 |
KEEP AS NON CORE |
Summary: IEA from InterPro mapping. Correct but broad -- the more specific term "fungal-type cell wall organization" (GO:0031505) is already annotated with experimental evidence.
Reason: Correct but subsumed by the more specific GO:0031505 (fungal-type cell wall organization) which is already annotated.
|
|
GO:0071944
cell periphery
|
HDA
PMID:26928762 One library to make them all: streamlining the creation of y... |
KEEP AS NON CORE |
Summary: HDA annotation from the SWAp-Tag high-throughput localization study (Yofe et al. 2016). CRH1 is a GPI-anchored cell wall protein at the cell surface, so cell periphery is correct. However, more specific terms (fungal-type cell wall, incipient cellular bud site) are already annotated with direct experimental evidence.
Reason: Correct but broad. The high-throughput dataset correctly places CRH1 at the cell periphery, but more specific localization terms are already available from focused studies.
Supporting Evidence:
PMID:26928762
we constructed and investigated a library of ∼1,800 strains carrying SWAT-GFP modules at the amino termini of endomembrane proteins
|
|
GO:0016757
glycosyltransferase activity
|
IDA
PMID:23919454 A novel fluorescence assay and catalytic properties of Crh1 ... |
ACCEPT |
Summary: IDA annotation based on Mazan et al. (2013). Heterologously expressed CRH1 was shown to transfer chitin chains to glucan oligosaccharide acceptors in a direct in vitro assay using fluorescently-labeled substrates. This is the most direct demonstration of CRH1's transglycosylase activity.
Reason: Core molecular function of CRH1 demonstrated by direct biochemical assay. CRH1 uses soluble chitin derivatives as donors and glucan-derived oligosaccharides as acceptors to catalyze transglycosylation.
Supporting Evidence:
PMID:23919454
Both proteins act as chitin transglycosylases; they use soluble chitin derivatives, such as carboxymethyl chitin, glycol-chitin and/or N-acetyl chito-oligosaccharides of DP (degree of polymerization)≥5 as the oligoglycosyl donors, and oligosaccharides derived from chitin, β-(1,3)-glucan (laminarin) and β-(1,6)-glucan (pustulan), fluorescently labelled with sulforhodamine or FITC as acceptors
|
|
GO:0000131
incipient cellular bud site
|
IDA
PMID:10757808 A novel family of cell wall-related proteins regulated diffe... |
ACCEPT |
Summary: IDA annotation based on Rodriguez-Pena et al. (2000). Crh1-GFP was observed at the incipient bud site by confocal fluorescence microscopy. CRH1 localizes to chitin-rich areas where cell wall remodeling occurs during polarized growth.
Reason: Correct and specific. CRH1-GFP localization to the incipient bud site is consistent with its function in chitin-glucan cross-linking during bud emergence.
Supporting Evidence:
PMID:10757808
Crh1-green fluorescent protein was found at the incipient bud site, around the septum area in later stages of budding, and in ascospore envelopes
|
|
GO:0006030
chitin metabolic process
|
IMP
PMID:18694928 Assembly of the yeast cell wall. Crh1p and Crh2p act as tran... |
ACCEPT |
Summary: IMP annotation based on Cabib et al. (2008). Mutant phenotype analysis showed that CRH genes are required for chitin transfer to glucan. Fluorescent chitin acceptor labeling in vivo was dependent on CRH genes. This directly demonstrates CRH1 involvement in chitin metabolism.
Reason: Core biological process. CRH1 transfers chitin chains to glucan acceptors, directly participating in chitin metabolism. The crh1/crh2 double mutant completely lacks chitin-glucan cross-links.
Supporting Evidence:
PMID:18694928
the Crh proteins act by transferring chitin chains to beta(1-6)glucan, with a newly observed high activity in the bud scar
|
|
GO:0006030
chitin metabolic process
|
IGI
PMID:18694928 Assembly of the yeast cell wall. Crh1p and Crh2p act as tran... |
ACCEPT |
Summary: IGI annotation based on genetic interaction between CRH1 and CRH2 (SGD:S000000766). Cabib et al. (2008) showed that CRH1 and CRH2 are redundantly required for chitin transfer to glucan; the double mutant shows complete loss of chitin-glucan cross-links while single mutants show partial loss.
Reason: Correct. The genetic interaction between CRH1 and CRH2 demonstrates redundant function in chitin metabolism.
Supporting Evidence:
PMID:18694928
In vivo, fluorescence was detected in bud scars and at a lower level in the cell contour, both being dependent on the CRH genes
|
|
GO:0009277
fungal-type cell wall
|
IDA
PMID:10757808 A novel family of cell wall-related proteins regulated diffe... |
ACCEPT |
Summary: IDA annotation based on Rodriguez-Pena et al. (2000). Crh1-GFP localized to the cell surface, particularly in chitin-rich areas. The protein is a GPI-CWP covalently attached to the cell wall.
Reason: Core localization. CRH1 is a GPI-anchored cell wall protein, demonstrated by GFP localization at the cell surface in chitin-rich regions.
Supporting Evidence:
PMID:10757808
Crh1 and Crh2 are localized at the cell surface, particularly in chitin-rich areas
|
|
GO:0009277
fungal-type cell wall
|
IDA
PMID:15781460 Comprehensive proteomic analysis of Saccharomyces cerevisiae... |
ACCEPT |
Summary: IDA annotation based on Yin et al. (2005). CRH1 was identified as a covalently-bound cell wall protein by mass spectrometry of isolated cell walls. Specifically identified as a GPI-modified CWP.
Reason: Direct proteomic identification of CRH1 in isolated cell walls confirms cell wall localization.
Supporting Evidence:
PMID:15781460
The identified proteins include 12 predicted glycosylphosphatidylinositol-modified CWPs ...seven of the identified proteins (Gas1p, Gas3p, Gas5p, Crh1p, Utr2p, Scw4p, and Scw10p) are classified as glycoside hydrolases
|
|
GO:0016757
glycosyltransferase activity
|
IMP
PMID:18694928 Assembly of the yeast cell wall. Crh1p and Crh2p act as tran... |
ACCEPT |
Summary: IMP annotation based on Cabib et al. (2008). Mutant phenotype analysis showed CRH-dependent transfer of chitin to glucan both in vivo (fluorescent acceptor labeling) and in digitonin-permeabilized cells. The linking reaction required CRH genes.
Reason: Core molecular function demonstrated by mutant phenotype. Loss of CRH genes eliminates chitin-to-glucan transglycosylation activity.
Supporting Evidence:
PMID:18694928
The linking reaction was also shown in digitonin-permeabilized cells, with UDP-N-acetylglucosamine as the substrate for nascent chitin production. Both the nucleotide and the Crh proteins were required here
|
|
GO:0016757
glycosyltransferase activity
|
IGI
PMID:18694928 Assembly of the yeast cell wall. Crh1p and Crh2p act as tran... |
ACCEPT |
Summary: IGI annotation based on genetic interaction between CRH1 and CRH2. The redundant requirement of both genes for full transglycosylase activity was demonstrated by comparing single and double mutants.
Reason: Correct. CRH1 and CRH2 have redundant glycosyltransferase activity for chitin-glucan cross-linking.
Supporting Evidence:
PMID:18694928
In vivo, fluorescence was detected in bud scars and at a lower level in the cell contour, both being dependent on the CRH genes
|
|
GO:0031505
fungal-type cell wall organization
|
IMP
PMID:18694928 Assembly of the yeast cell wall. Crh1p and Crh2p act as tran... |
ACCEPT |
Summary: IMP annotation based on Cabib et al. (2008). crh1/crh2 double mutants show altered cell wall architecture with loss of chitin-glucan cross-links and increased alkali-soluble glucan. Deletion aggravated defects of fks1 and gas1 mutants.
Reason: Core biological process. CRH1 is essential for proper cell wall organization through chitin-glucan cross-linking.
Supporting Evidence:
PMID:18694928
The importance of transglycosylation for cell wall assembly is thus firmly established
|
|
GO:0031505
fungal-type cell wall organization
|
IGI
PMID:18694928 Assembly of the yeast cell wall. Crh1p and Crh2p act as tran... |
ACCEPT |
Summary: IGI annotation based on genetic interaction between CRH1 and CRH2. Single and double mutant analysis demonstrates their redundant contribution to cell wall organization.
Reason: Correct. The genetic interaction confirms both CRH1 and CRH2 contribute to cell wall organization.
Supporting Evidence:
PMID:18694928
The importance of transglycosylation for cell wall assembly is thus firmly established
|
Q: Is there a more specific GO term for chitin transglycosylase activity that could distinguish the primary transglycosylation function from the secondary endochitinase activity? Currently both activities are annotated under different parent terms (glycosyltransferase vs endochitinase), but there is no specific "chitin transglycosylase activity" term in GO.
Q: What is the relative in vivo contribution of the endochitinase activity versus the transglycosylase activity of CRH1? Is the chitinase activity biologically relevant or simply a side reaction of the GH16 catalytic mechanism?
Experiment: Use compartment-specific fluorescent chitin acceptors with conditional CRH1 expression to determine whether transglycosylation rates differ at different cell surface locations. Compare with CRH2 localization and activity patterns.
Hypothesis: CRH1 chitin transglycosylase activity may have distinct substrate preferences in different cell wall compartments (bud scar vs lateral wall vs septum).
Type: fluorescence microscopy with functional assay
---
provider: bioreason-pro
model: SFT
source: huggingface.co/datasets/wanglab/protein_catalogue
date: '2026-04-04'
uniprot_id: P53301
gene: CRH1
organism: Saccharomyces cerevisiae (strain ATCC 204508 / S288c) (Baker's yeast)
---
## Thinking Trace
I begin with the InterPro architecture. The N-terminal half is dominated by glycoside hydrolase family-16 signatures: IPR050546 (Glycosyl Hydrolase Family 16, residues 11–258) overlaps with two concordant domain calls, IPR000757 (Beta-glucanase-like, N-terminal domain, residues 34–260) and IPR000757 (Beta-glucanase-like, N-terminal domain, residues 69–235), all embedded within the broader IPR013320 (Concanavalin A-like lectin/glucanase domain superfamily, residues 52–257). This cluster defines the canonical GH16 β-jelly-roll catalytic fold that uses a retaining double-displacement mechanism to cleave β-1,3-glucan with a catalytic glutamate pair and to transfer the glycan to an acceptor. The entire polypeptide is further classified by IPR017168 (CRH-like family, residues 18–485), which specifies the specialized fungal clade of GH16 enzymes that act as chitin β-glucan transglycosylases. The ordered layout—an N-terminal GH16 catalytic core followed by a C-terminal region that typically harbors a GPI-attachment signal—creates a secretory, cell-surface enzyme optimized to remodel the cell wall by forming new β-1,3-glucan linkages to chitin.
This GH16/CRH-like architecture causes glycosyltransfer-like chemistry in a transglycosylation mode: the catalytic nucleophile forms a glycosyl–enzyme intermediate from a β-1,3-glucan donor, then transfers the glucan to the non-reducing end of chitin, extending the chitin chain. That mechanism directly supports the molecular function formalized as GO:0016757 glycosyltransferase activity, here realized as a retaining transglycosylation rather than a simple hydrolysis.
By extending chitin with β-1,3-glucan and cross-linking these polymers, the enzyme drives the assembly and maturation of the fungal cell wall. This places it squarely in GO:0006037 cell wall chitin metabolic process and, at a higher organizational level, in GO:0031505 fungal-type cell wall organization. The CRH-like family is known to be essential for robust wall architecture, and the catalytic logic here provides the cross-linking needed to integrate chitin with the glucan network.
The presence of a GPI-anchor signal inferred from the CRH-like family and the absence of transmembrane helices indicate extracellular targeting via the secretory pathway, with the enzyme attached to the outer leaflet of the plasma membrane and covalently or noncovalently incorporated into the wall matrix. This explains localization to the GO:0009277 fungal-type cell wall and, during polarized growth, enrichment at the GO:0000131 incipient cellular bud site where wall construction is initiated. The GPI anchor ensures the catalytic domain is presented to the periplasmic/cell wall space, where its substrates—chitin and β-1,3-glucan—reside.
Mechanistically, the enzyme likely operates in concert with other wall-remodeling factors. A plausible partner is the probable glycosidase CRH2, which can provide complementary transglycosylation or processing of glucan acceptors, forming a cooperative pair that tunes cross-link density. The 1,3-beta-glucanosyltransferase GAS1 can elongate β-1,3-glucan chains that then become donors or acceptors for this enzyme, creating a feed-forward loop that builds robust glucan scaffolds. Endo-beta-1,3-glucanase can trim or open glucan chains to generate optimal acceptor termini, increasing efficiency of transglycosylation. Cell wall proteins with GPI-attachment sites, including mannoproteins that mark birth scars, likely serve as structural substrates or scaffolds that spatially constrain the reaction during bud formation and daughter-cell differentiation. Together, these interactions would coordinate polymer remodeling and cross-linking precisely where wall expansion and septation occur.
## Functional Summary
A GPI-anchored cell-surface transglycosylase in baker’s yeast that extends chitin chains using β-1,3-glucan as a donor, thereby cross-linking chitin into the glucan network and strengthening the cell wall. Its GH16 catalytic core executes a retaining double-displacement reaction that transfers glucan to the non-reducing end of chitin, integrating polymers during wall assembly and polarized growth. The enzyme concentrates at nascent bud sites and birth scars, where it collaborates with glucanases, glucanosyltransferases, and other GPI-anchored mannoproteins to organize the wall architecture.
## UniProt Summary
Involved in cell wall construction. Extends chitin with beta-1,3-glucan. May be involved in the cross-linking of chitin to the glucan network of the cell wall.
## InterPro Domains
- IPR050546: Glycosyl Hydrolase Family 16 (family) [11-258]
- IPR017168: CRH-like (family) [18-485]
- IPR000757: Beta-glucanase-like, N-terminal domain (domain) [34-260]
- IPR013320: Concanavalin A-like lectin/glucanase domain superfamily (homologous_superfamily) [52-257]
- IPR000757: Beta-glucanase-like, N-terminal domain (domain) [69-235]
## GO Term Predictions
### Molecular Function
### Biological Process
### Cellular Component
Rodriguez-Pena et al. (2000) identified CRH1, CRH2, and CRR1 as a novel family of cell wall-related proteins with homology to bacterial beta-glucanases and eukaryotic endotransglycosidases. Deletion of CRH1 and CRH2 caused additive sensitivity to Congo Red and Calcofluor White (cell wall-perturbing agents). The putative glycosidase domain was critical for function. Crh1-GFP localized to incipient bud site, septum area in late budding, and ascospore envelopes. The alkali-soluble glucan fraction in crh1/crh2 double mutant was almost twice wild-type levels. PMID:10757808
Hamada et al. (1998) identified CRH1 as a GPI-dependent cell wall protein through genome-wide screening. PMID:9613572
Yin et al. (2005) confirmed CRH1 is covalently attached to cell wall via GPI remnants by comprehensive proteomic analysis using tandem mass spectrometry. PMID:15781460
Cabib et al. (2007) showed Crh1p and Crh2p are required for cross-linking chitin to beta(1-6)glucan. In crh1/crh2 double mutants, chitin linked to beta(1-6)glucan was completely absent. Heat stress (38C) increased chitin-beta(1-6)glucan cross-links and CRH1 expression (cell integrity pathway dependent). PMID:17302808
Cabib et al. (2008) demonstrated that Crh1p and Crh2p act as transglycosylases both in vivo and in vitro. Using fluorescent sulforhodamine-linked laminari-oligosaccharides as artificial chitin acceptors, they showed CRH-dependent fluorescence at bud scars and cell contour. The cell wall reaction was inhibited by chitooligosaccharides. PMID:18694928
Cabib (2009) developed two novel techniques showing Crh1p and Crh2p transfer chitin to BOTH beta(1-3)- and beta(1-6)glucan. Previous results suggesting residual chitin-beta(1-3)glucan links in crh1/crh2 mutants were due to chitinase contamination in zymolyase. All chitin in crh1/crh2 double mutants is free (unlinked). PMID:19734368
Mazan et al. (2013) heterologously expressed CRH1 and CRH2 in Pichia pastoris and characterized their catalytic properties:
- Both act as chitin transglycosylases
- Donors: soluble chitin derivatives (CM-chitin, glycol-chitin, chitooligosaccharides DP>=5)
- Acceptors: oligosaccharides from chitin, beta(1,3)-glucan (laminarin), beta(1,6)-glucan (pustulan)
- Minimal acceptor: 2 hexopyranose units; effectivity increases with chain length
- Both exhibit weak endochitinase activity (ratio of endo:exo ~4x higher in Crh1 vs Crh2)
- pH optimum: 3.5; temperature optimum: 37C
PMID:23919454
Yin et al. (2007) quantified CRH1 at 44,000 wall-bound copies per cell in log phase YPD. In gas1 mutants (constitutive cell wall integrity pathway), Crh1p levels increased ~3-5 fold. PMID:17617218
CRH1 is positively regulated by MPK1/SLT2 through the cell wall integrity signaling pathway via Rlm1 transcription factor. Expression is upregulated in response to cell wall damage (fks1 disruption) and heat stress. [PMID:10594829, PMID:11016834]
Yofe et al. (2016) SWAp-Tag (SWAT) high-throughput localization study assigned CRH1 to cell periphery. This is a high-throughput dataset (HDA evidence). PMID:26928762
CRH2 (YEL040w, also called UTR2) is the key paralog. CRH1 and CRH2 have redundant transglycosylase activity for chitin-glucan cross-linking. Single mutants show partial phenotypes; double mutants show complete loss of chitin cross-links. CRH1 is cell-cycle regulated and expressed during sporulation; CRH2 expression is constitutive during mitotic cycle.
CRH1 is a dual-function enzyme: primarily a chitin transglycosylase (transfers chitin to glucan acceptors) with secondary weak endochitinase activity. The GH16 catalytic domain uses a retaining mechanism with a catalytic glutamate pair (E134 nucleophile, E138 proton donor, by homology). The enzyme forms a glycosyl-enzyme intermediate from a chitin donor, then transfers the chitin chain to beta(1-3)- or beta(1-6)glucan acceptors. This cross-links chitin into the cell wall glucan network, which is essential for cell wall integrity.
Source: CRH1-deep-research-bioreason-sft.md
The BioReason functional summary describes CRH1 as:
A GPI-anchored cell-surface transglycosylase in baker's yeast that extends chitin chains using beta-1,3-glucan as a donor, thereby cross-linking chitin into the glucan network and strengthening the cell wall. Its GH16 catalytic core executes a retaining double-displacement reaction that transfers glucan to the non-reducing end of chitin, integrating polymers during wall assembly and polarized growth. The enzyme concentrates at nascent bud sites and birth scars, where it collaborates with glucanases, glucanosyltransferases, and other GPI-anchored mannoproteins to organize the wall architecture.
This summary captures the essential biology of CRH1 reasonably well but contains a notable mechanistic error and some omissions.
Correctness issues:
Donor-acceptor direction is reversed. The BioReason summary states CRH1 "extends chitin chains using beta-1,3-glucan as a donor" and "transfers glucan to the non-reducing end of chitin." This is backwards. According to Cabib et al. (2008, DOI) and Mazan et al. (2013, DOI), CRH1 uses chitin (or chitin derivatives) as the glycosyl donor and glucan oligosaccharides as the acceptor. The enzyme transfers chitin chains TO glucan, not glucan to chitin. The BioReason thinking trace also incorrectly states "the catalytic nucleophile forms a glycosyl-enzyme intermediate from a beta-1,3-glucan donor, then transfers the glucan to the non-reducing end of chitin." This reversal of donor and acceptor is a significant mechanistic error.
The thinking trace describes "cell wall chitin metabolic process" (GO:0006037). The actual GO term used in annotations is GO:0006030 (chitin metabolic process). GO:0006037 does not appear in the GOA for CRH1. This may be a hallucinated or incorrectly recalled GO term ID, though "cell wall chitin metabolic process" would be a reasonable concept.
The claim about "Endo-beta-1,3-glucanase" as a collaborator is vague. The thinking trace mentions this generically but does not identify a specific gene. In S. cerevisiae cell wall biology, the relevant enzymes are BGL2 (endo-beta-1,3-glucanase) and the GAS family (Gas1p etc., beta-1,3-glucanosyltransferases). The mention of GAS1 as a collaborator is appropriate.
Completeness issues:
No mention of the CRH2/UTR2 paralog relationship. The CRH1-CRH2 redundancy is central to understanding CRH1 function. The crh1/crh2 double mutant completely lacks chitin-glucan cross-links (PMID:17302808, DOI; PMID:19734368, DOI), while single mutants show only partial defects. This is one of the best-characterized examples of redundant cell wall enzymes.
No mention of the secondary endochitinase activity. UniProt assigns EC 3.2.1.14 to CRH1, and Mazan et al. (2013) demonstrated weak but measurable endochitinase activity in vitro. The dual chitinase/transglycosylase nature is biologically notable and relevant for annotation.
No mention of cell-cycle regulation. CRH1 is cell-cycle regulated and expressed during sporulation, while CRH2 is constitutive during the mitotic cycle (PMID:10757808, DOI). This differential regulation is key to understanding the division of labor between the paralogs.
No mention of regulation by the cell wall integrity pathway. CRH1 is induced by heat stress and cell wall damage through MPK1/SLT2 signaling and the RLM1 transcription factor (PMID:10594829, DOI; PMID:11016834, DOI; PMID:17302808).
No mention of quantitative protein data. CRH1 is present at approximately 44,000 wall-bound copies per cell in log phase (PMID:17617218, DOI), making it one of the more abundant cell wall proteins.
The GO term predictions section is empty. No MF, BP, or CC predictions were made, though the thinking trace and functional summary contain implicit predictions. This appears to be a formatting issue with the BioReason output rather than a content gap.
All PMIDs cited in the GOA annotations were verified as real publications in PubMed:
- PMID:10757808 -- Rodriguez-Pena et al. (2000) Mol Cell Biol (DOI)
- PMID:15781460 -- Yin et al. (2005) J Biol Chem (DOI)
- PMID:18694928 -- Cabib et al. (2008) J Biol Chem (DOI)
- PMID:23919454 -- Mazan et al. (2013) Biochem J (DOI)
- PMID:26928762 -- Yofe et al. (2016) Nat Methods (DOI)
Additional key references not in GOA but important for CRH1 biology:
- PMID:17302808 -- Cabib et al. (2007) Mol Microbiol (DOI)
- PMID:19734368 -- Cabib (2009) Eukaryot Cell (DOI)
- PMID:9613572 -- Hamada et al. (1998) Mol Gen Genet (DOI)
- PMID:10594829 -- Jung & Levin (1999) Mol Microbiol (DOI)
- PMID:11016834 -- Terashima et al. (2000) Mol Gen Genet (DOI)
- PMID:17617218 -- Yin et al. (2007) FEMS Yeast Res (DOI)
The BioReason report itself does not explicitly cite PMIDs in its thinking trace or functional summary. All assertions are derived from InterPro domain architecture reasoning rather than direct literature citations.
The InterPro2GO annotations for CRH1 include:
- GO:0004553 hydrolase activity, hydrolyzing O-glycosyl compounds (from IPR000757)
- GO:0005975 carbohydrate metabolic process (from IPR000757)
- GO:0016798 hydrolase activity, acting on glycosyl bonds (from IPR017168)
- GO:0071555 cell wall organization (from IPR017168)
The BioReason narrative adds substantial mechanistic context beyond raw InterPro2GO mappings: it correctly identifies the transglycosylase mechanism, the GPI-anchor, the bud site localization, and the cell wall cross-linking function. These insights go well beyond what InterPro2GO provides. The main error (reversed donor-acceptor direction) is a mechanistic detail that demonstrates the limitations of reasoning from domain architecture alone without careful interpretation of the specific reaction catalyzed by the CRH subfamily.
The thinking trace is well-structured and demonstrates competent domain architecture analysis. It correctly identifies the GH16 beta-jelly-roll catalytic fold, the CRH-like family specialization, and the GPI-anchor signal. The reasoning about retaining double-displacement mechanism and catalytic glutamate pair is sound.
The main weakness is the reversed reaction direction. The BioReason model appears to have defaulted to a general GH16 glucanase narrative ("cleave beta-1,3-glucan") rather than recognizing that the CRH subfamily specifically transfers chitin to glucan, not glucan to chitin. This is a subtle but important distinction that requires gene-specific literature knowledge.
The proposed collaborators (GAS1, CRH2, endo-beta-1,3-glucanase) are reasonable and consistent with known cell wall biology, though stated somewhat generically without gene-specific evidence for direct interactions.
Overall, the BioReason prediction for CRH1 is substantially better than for many other genes, reflecting the fact that CRH1's function is closely tied to its domain architecture. The main limitation is the donor-acceptor reversal, which would lead to an incorrect mechanistic model if taken at face value.
id: P53301
gene_symbol: CRH1
product_type: PROTEIN
status: COMPLETE
tags:
- UPB
- cell-wall
- transglycosylase
- GH16
- GPI-CWP
taxon:
id: NCBITaxon:559292
label: Saccharomyces cerevisiae
description: >-
CRH1 (Congo Red Hypersensitive protein 1) encodes a GPI-anchored cell wall transglycosylase
of the GH16 family that cross-links chitin to both beta(1-3)- and beta(1-6)-glucan in the
S. cerevisiae cell wall. The enzyme uses a retaining double-displacement mechanism: it cleaves
a chitin donor chain and transfers it to glucan acceptors, thereby integrating chitin into the
glucan network. CRH1 has a secondary weak endochitinase activity (EC 3.2.1.14) but its primary
biological role is as a chitin transglycosylase (EC 2.4.-.-). The protein is GPI-anchored at the
cell surface and concentrated at chitin-rich areas including the incipient bud site, septum, and
bud scars. CRH1 acts redundantly with its paralog CRH2/UTR2; the double mutant completely lacks
chitin-glucan cross-links and shows strong sensitivity to Congo Red and Calcofluor White. CRH1
expression is cell-cycle regulated, induced during sporulation, and upregulated by the cell wall
integrity pathway (MPK1/RLM1) in response to heat stress and cell wall damage. Present at
approximately 44,000 wall-bound copies per cell in log phase.
existing_annotations:
- term:
id: GO:0005576
label: extracellular region
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
IBA annotation from phylogenetic inference. CRH1 is a GPI-anchored cell wall protein that
is secreted and covalently attached to the outer cell wall. While "extracellular region" is
not wrong for a secreted protein, the more specific and accurate term is "fungal-type cell
wall" (GO:0009277), which is already annotated with direct experimental evidence (IDA).
This IBA adds little information beyond the existing IDA annotations.
action: KEEP_AS_NON_CORE
reason: >-
Technically correct but too broad. CRH1 is a GPI-CWP covalently incorporated into the cell
wall, not a freely secreted extracellular protein. The IDA annotation to fungal-type cell wall
is more informative.
- term:
id: GO:0006030
label: chitin metabolic process
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
IBA annotation from phylogenetic inference. CRH1 is directly involved in chitin metabolic
process as a chitin transglycosylase that transfers chitin chains to glucan acceptors.
This is consistent with IMP and IGI evidence from PMID:18694928.
action: ACCEPT
reason: >-
Correct and supported by direct experimental evidence. CRH1 transfers chitin to glucan,
which is a chitin metabolic process.
- term:
id: GO:0031505
label: fungal-type cell wall organization
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
IBA annotation from phylogenetic inference. CRH1 is a key enzyme in fungal cell wall
organization, cross-linking chitin to the glucan network. This is consistent with IMP
and IGI evidence from PMID:18694928.
action: ACCEPT
reason: >-
Correct. CRH1 cross-links chitin to glucan, which is an essential step in cell wall
organization. Well-supported by multiple lines of evidence.
- term:
id: GO:0009277
label: fungal-type cell wall
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
IBA annotation from phylogenetic inference for cell wall localization. CRH1 is a GPI-CWP
covalently attached to the cell wall, confirmed by mass spectrometry (PMID:15781460) and
GFP localization (PMID:10757808). Consistent with IDA evidence.
action: ACCEPT
reason: >-
Correct. CRH1 is covalently linked to the cell wall via its GPI anchor remnant. Multiple
IDA annotations confirm this.
- term:
id: GO:0016757
label: glycosyltransferase activity
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
IBA annotation from phylogenetic inference. CRH1 is a chitin transglycosylase that
transfers chitin chains to glucan acceptors, which is a glycosyltransferase activity.
Supported by IDA evidence from PMID:23919454 and IMP/IGI from PMID:18694928.
action: ACCEPT
reason: >-
Correct. Transglycosylase activity is a form of glycosyltransferase activity. This is the
core molecular function of CRH1.
- term:
id: GO:0004553
label: hydrolase activity, hydrolyzing O-glycosyl compounds
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
IEA from InterPro mapping (IPR000757 Beta-glucanase-like domain). CRH1 does have weak
endochitinase activity (EC 3.2.1.14) as demonstrated by Mazan et al. (2013), so the
annotation is not incorrect. However, the primary function is transglycosylase activity,
not hydrolase activity. The hydrolytic activity is secondary and weak.
action: KEEP_AS_NON_CORE
reason: >-
Technically correct -- CRH1 has documented weak endochitinase activity (PMID:23919454) --
but the primary evolved function is transglycosylation, not hydrolysis. This InterPro-based
annotation reflects the ancestral GH16 hydrolase function rather than the derived
transglycosylase specialization.
supported_by:
- reference_id: file:yeast/CRH1/CRH1-deep-research-bioreason-sft.md
supporting_text: >-
[BioReason identifies the GH16 catalytic core as executing a retaining
double-displacement reaction, consistent with the transglycosylase being the primary
function rather than simple hydrolysis]
- term:
id: GO:0005975
label: carbohydrate metabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
IEA from InterPro mapping. CRH1 is indeed involved in carbohydrate metabolism (chitin and
glucan processing). This is correct but very broad -- the more specific term "chitin
metabolic process" (GO:0006030) is already annotated.
action: KEEP_AS_NON_CORE
reason: >-
Correct but very broad. Subsumed by the more specific GO:0006030 (chitin metabolic process)
which is already annotated with experimental evidence.
- term:
id: GO:0008843
label: endochitinase activity
evidence_type: IEA
original_reference_id: GO_REF:0000003
review:
summary: >-
IEA from EC number mapping (EC 3.2.1.14). Mazan et al. (2013) demonstrated weak
endochitinase activity for heterologously expressed CRH1. The endo:exo chitinase ratio
was approximately 4-fold higher in Crh1 than Crh2. However, the chitinase activity is
secondary to the primary transglycosylase function.
action: KEEP_AS_NON_CORE
reason: >-
Correct. CRH1 has documented endochitinase activity (PMID:23919454), but this is a
secondary activity. The primary molecular function is chitin transglycosylase activity.
supported_by:
- reference_id: PMID:23919454
supporting_text: >-
Both proteins exhibited a weak chitinolytic activity in different assays whereby the
ratio of endo- compared with exo-chitinase activity was approximately 4-fold higher
in Crh1 than in Crh2
- term:
id: GO:0009277
label: fungal-type cell wall
evidence_type: IEA
original_reference_id: GO_REF:0000117
review:
summary: >-
IEA from ARBA machine learning model. Correct -- CRH1 is covalently linked to the
fungal-type cell wall. Redundant with IDA annotations from PMID:10757808 and PMID:15781460.
action: ACCEPT
reason: >-
Correct and consistent with multiple lines of direct experimental evidence.
- term:
id: GO:0016020
label: membrane
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: >-
IEA from UniProtKB subcellular location mapping. CRH1 is GPI-anchored to the outer leaflet
of the plasma membrane before being transferred to the cell wall. The annotation is technically
correct but imprecise. CRH1 is primarily a cell wall protein, not a membrane protein in the
traditional sense. The GPI anchor transiently associates it with the membrane during transport.
action: KEEP_AS_NON_CORE
reason: >-
Technically correct (GPI-anchored to membrane) but misleading for CRH1, which is primarily
a covalently-linked cell wall protein. The GPI anchor is processed during transfer to the
cell wall.
- term:
id: GO:0016798
label: hydrolase activity, acting on glycosyl bonds
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
IEA from InterPro mapping (IPR017168 CRH-like family). CRH1 has weak endochitinase
activity, so hydrolysis of glycosyl bonds is technically correct. However, this is a
parent term of endochitinase activity (GO:0008843) which is already annotated, and
the primary function is transglycosylation rather than hydrolysis.
action: KEEP_AS_NON_CORE
reason: >-
Correct but broad and redundant. The more specific endochitinase activity (GO:0008843)
is already annotated. The primary function is transglycosylase, not hydrolase.
- term:
id: GO:0031505
label: fungal-type cell wall organization
evidence_type: IEA
original_reference_id: GO_REF:0000117
review:
summary: >-
IEA from ARBA machine learning model. Correct -- CRH1 is essential for cell wall
organization through chitin-glucan cross-linking. Consistent with IMP/IGI evidence.
action: ACCEPT
reason: >-
Correct and consistent with experimental evidence from PMID:18694928.
- term:
id: GO:0071555
label: cell wall organization
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
IEA from InterPro mapping. Correct but broad -- the more specific term "fungal-type
cell wall organization" (GO:0031505) is already annotated with experimental evidence.
action: KEEP_AS_NON_CORE
reason: >-
Correct but subsumed by the more specific GO:0031505 (fungal-type cell wall organization)
which is already annotated.
- term:
id: GO:0071944
label: cell periphery
evidence_type: HDA
original_reference_id: PMID:26928762
review:
summary: >-
HDA annotation from the SWAp-Tag high-throughput localization study (Yofe et al. 2016).
CRH1 is a GPI-anchored cell wall protein at the cell surface, so cell periphery is correct.
However, more specific terms (fungal-type cell wall, incipient cellular bud site) are already
annotated with direct experimental evidence.
action: KEEP_AS_NON_CORE
reason: >-
Correct but broad. The high-throughput dataset correctly places CRH1 at the cell periphery,
but more specific localization terms are already available from focused studies.
supported_by:
- reference_id: PMID:26928762
supporting_text: >-
we constructed and investigated a library of ∼1,800 strains carrying SWAT-GFP modules
at the amino termini of endomembrane proteins
- term:
id: GO:0016757
label: glycosyltransferase activity
evidence_type: IDA
original_reference_id: PMID:23919454
review:
summary: >-
IDA annotation based on Mazan et al. (2013). Heterologously expressed CRH1 was shown
to transfer chitin chains to glucan oligosaccharide acceptors in a direct in vitro assay
using fluorescently-labeled substrates. This is the most direct demonstration of CRH1's
transglycosylase activity.
action: ACCEPT
reason: >-
Core molecular function of CRH1 demonstrated by direct biochemical assay. CRH1 uses
soluble chitin derivatives as donors and glucan-derived oligosaccharides as acceptors
to catalyze transglycosylation.
supported_by:
- reference_id: PMID:23919454
supporting_text: >-
Both proteins act as chitin transglycosylases; they use soluble chitin derivatives,
such as carboxymethyl chitin, glycol-chitin and/or N-acetyl chito-oligosaccharides of
DP (degree of polymerization)≥5 as the oligoglycosyl donors, and oligosaccharides
derived from chitin, β-(1,3)-glucan (laminarin) and β-(1,6)-glucan (pustulan),
fluorescently labelled with sulforhodamine or FITC as acceptors
- term:
id: GO:0000131
label: incipient cellular bud site
evidence_type: IDA
original_reference_id: PMID:10757808
review:
summary: >-
IDA annotation based on Rodriguez-Pena et al. (2000). Crh1-GFP was observed at the
incipient bud site by confocal fluorescence microscopy. CRH1 localizes to chitin-rich
areas where cell wall remodeling occurs during polarized growth.
action: ACCEPT
reason: >-
Correct and specific. CRH1-GFP localization to the incipient bud site is consistent
with its function in chitin-glucan cross-linking during bud emergence.
supported_by:
- reference_id: PMID:10757808
supporting_text: >-
Crh1-green fluorescent protein was found at the incipient bud site, around the septum
area in later stages of budding, and in ascospore envelopes
- term:
id: GO:0006030
label: chitin metabolic process
evidence_type: IMP
original_reference_id: PMID:18694928
review:
summary: >-
IMP annotation based on Cabib et al. (2008). Mutant phenotype analysis showed that CRH
genes are required for chitin transfer to glucan. Fluorescent chitin acceptor labeling
in vivo was dependent on CRH genes. This directly demonstrates CRH1 involvement in
chitin metabolism.
action: ACCEPT
reason: >-
Core biological process. CRH1 transfers chitin chains to glucan acceptors, directly
participating in chitin metabolism. The crh1/crh2 double mutant completely lacks
chitin-glucan cross-links.
supported_by:
- reference_id: PMID:18694928
supporting_text: >-
the Crh proteins act by transferring chitin chains to beta(1-6)glucan, with a newly
observed high activity in the bud scar
- term:
id: GO:0006030
label: chitin metabolic process
evidence_type: IGI
original_reference_id: PMID:18694928
review:
summary: >-
IGI annotation based on genetic interaction between CRH1 and CRH2 (SGD:S000000766).
Cabib et al. (2008) showed that CRH1 and CRH2 are redundantly required for chitin
transfer to glucan; the double mutant shows complete loss of chitin-glucan cross-links
while single mutants show partial loss.
action: ACCEPT
reason: >-
Correct. The genetic interaction between CRH1 and CRH2 demonstrates redundant function
in chitin metabolism.
supported_by:
- reference_id: PMID:18694928
supporting_text: >-
In vivo, fluorescence was detected in bud scars and at a lower level in the cell contour,
both being dependent on the CRH genes
- term:
id: GO:0009277
label: fungal-type cell wall
evidence_type: IDA
original_reference_id: PMID:10757808
review:
summary: >-
IDA annotation based on Rodriguez-Pena et al. (2000). Crh1-GFP localized to the cell
surface, particularly in chitin-rich areas. The protein is a GPI-CWP covalently attached
to the cell wall.
action: ACCEPT
reason: >-
Core localization. CRH1 is a GPI-anchored cell wall protein, demonstrated by GFP
localization at the cell surface in chitin-rich regions.
supported_by:
- reference_id: PMID:10757808
supporting_text: >-
Crh1 and Crh2 are localized at the cell surface, particularly in chitin-rich areas
- term:
id: GO:0009277
label: fungal-type cell wall
evidence_type: IDA
original_reference_id: PMID:15781460
review:
summary: >-
IDA annotation based on Yin et al. (2005). CRH1 was identified as a covalently-bound
cell wall protein by mass spectrometry of isolated cell walls. Specifically identified
as a GPI-modified CWP.
action: ACCEPT
reason: >-
Direct proteomic identification of CRH1 in isolated cell walls confirms cell wall
localization.
supported_by:
- reference_id: PMID:15781460
supporting_text: >-
The identified proteins include 12 predicted glycosylphosphatidylinositol-modified CWPs
...seven of the identified proteins (Gas1p, Gas3p, Gas5p, Crh1p, Utr2p, Scw4p, and
Scw10p) are classified as glycoside hydrolases
- term:
id: GO:0016757
label: glycosyltransferase activity
evidence_type: IMP
original_reference_id: PMID:18694928
review:
summary: >-
IMP annotation based on Cabib et al. (2008). Mutant phenotype analysis showed
CRH-dependent transfer of chitin to glucan both in vivo (fluorescent acceptor labeling)
and in digitonin-permeabilized cells. The linking reaction required CRH genes.
action: ACCEPT
reason: >-
Core molecular function demonstrated by mutant phenotype. Loss of CRH genes eliminates
chitin-to-glucan transglycosylation activity.
supported_by:
- reference_id: PMID:18694928
supporting_text: >-
The linking reaction was also shown in digitonin-permeabilized cells, with
UDP-N-acetylglucosamine as the substrate for nascent chitin production. Both the
nucleotide and the Crh proteins were required here
- term:
id: GO:0016757
label: glycosyltransferase activity
evidence_type: IGI
original_reference_id: PMID:18694928
review:
summary: >-
IGI annotation based on genetic interaction between CRH1 and CRH2. The redundant
requirement of both genes for full transglycosylase activity was demonstrated by
comparing single and double mutants.
action: ACCEPT
reason: >-
Correct. CRH1 and CRH2 have redundant glycosyltransferase activity for chitin-glucan
cross-linking.
supported_by:
- reference_id: PMID:18694928
supporting_text: >-
In vivo, fluorescence was detected in bud scars and at a lower level in the cell
contour, both being dependent on the CRH genes
- term:
id: GO:0031505
label: fungal-type cell wall organization
evidence_type: IMP
original_reference_id: PMID:18694928
review:
summary: >-
IMP annotation based on Cabib et al. (2008). crh1/crh2 double mutants show altered
cell wall architecture with loss of chitin-glucan cross-links and increased alkali-soluble
glucan. Deletion aggravated defects of fks1 and gas1 mutants.
action: ACCEPT
reason: >-
Core biological process. CRH1 is essential for proper cell wall organization through
chitin-glucan cross-linking.
supported_by:
- reference_id: PMID:18694928
supporting_text: >-
The importance of transglycosylation for cell wall assembly is thus firmly established
- term:
id: GO:0031505
label: fungal-type cell wall organization
evidence_type: IGI
original_reference_id: PMID:18694928
review:
summary: >-
IGI annotation based on genetic interaction between CRH1 and CRH2. Single and double
mutant analysis demonstrates their redundant contribution to cell wall organization.
action: ACCEPT
reason: >-
Correct. The genetic interaction confirms both CRH1 and CRH2 contribute to cell wall
organization.
supported_by:
- reference_id: PMID:18694928
supporting_text: >-
The importance of transglycosylation for cell wall assembly is thus firmly established
core_functions:
- description: >-
CRH1 is a GPI-anchored chitin transglycosylase that cross-links chitin to glucan
polymers in the yeast cell wall. It cleaves chitin donor chains and transfers them to
beta(1-3)- and beta(1-6)-glucan acceptors via a retaining glycosyl transfer mechanism.
This cross-linking activity is essential for cell wall integrity and is the primary
evolved function of CRH1, operating at chitin-rich sites during polarized growth.
molecular_function:
id: GO:0016757
label: glycosyltransferase activity
directly_involved_in:
- id: GO:0006030
label: chitin metabolic process
- id: GO:0031505
label: fungal-type cell wall organization
locations:
- id: GO:0009277
label: fungal-type cell wall
- id: GO:0000131
label: incipient cellular bud site
supported_by:
- reference_id: PMID:18694928
supporting_text: >-
the Crh proteins act by transferring chitin chains to beta(1-6)glucan, with a newly
observed high activity in the bud scar
- reference_id: PMID:23919454
supporting_text: >-
Both proteins act as chitin transglycosylases; they use soluble chitin derivatives,
such as carboxymethyl chitin, glycol-chitin and/or N-acetyl chito-oligosaccharides of
DP (degree of polymerization)≥5 as the oligoglycosyl donors, and oligosaccharides
derived from chitin, β-(1,3)-glucan (laminarin) and β-(1,6)-glucan (pustulan),
fluorescently labelled with sulforhodamine or FITC as acceptors
- reference_id: PMID:19734368
supporting_text: >-
Crh1p and Crh2p catalyze the transfer of chitin to both beta(1-3)- and beta(1-6)glucan,
and the biosynthetic mechanism for all chitin cross-links in the cell wall has been
established
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:0000033
title: Annotation inferences using phylogenetic trees
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: PMID:10757808
title: >-
A novel family of cell wall-related proteins regulated differently during the yeast
life cycle.
findings:
- statement: >-
CRH1 and CRH2 encode a novel family of cell wall proteins with homology to
beta-glucanases. Deletion causes Congo Red sensitivity. CRH1-GFP localizes to
incipient bud site, septum, and ascospore envelopes.
supporting_text: >-
Crh1-green fluorescent protein was found at the incipient bud site, around the septum
area in later stages of budding, and in ascospore envelopes...the alkali-soluble glucan
fraction in the crh1Delta crh2Delta strain was almost twice the level in the wild-type
- id: PMID:15781460
title: >-
Comprehensive proteomic analysis of Saccharomyces cerevisiae cell walls: identification
of proteins covalently attached via glycosylphosphatidylinositol remnants or mild
alkali-sensitive linkages.
findings:
- statement: >-
CRH1 identified as a GPI-modified cell wall protein by mass spectrometry of isolated
cell walls.
supporting_text: >-
The identified proteins include 12 predicted glycosylphosphatidylinositol-modified CWPs
...seven of the identified proteins (Gas1p, Gas3p, Gas5p, Crh1p, Utr2p, Scw4p, and
Scw10p) are classified as glycoside hydrolases
- id: PMID:17302808
title: >-
Crh1p and Crh2p are required for the cross-linking of chitin to beta(1-6)glucan in the
Saccharomyces cerevisiae cell wall.
findings:
- statement: >-
CRH1 and CRH2 are required for chitin-beta(1-6)glucan cross-links. Double mutant
completely lacks these cross-links. Heat stress increases cross-linking and CRH1
expression via cell integrity pathway.
supporting_text: >-
chitin linked to beta(1-6)glucan is diminished in mutants of the CRH1 or the CRH2/UTR2
gene and completely absent in a double mutant...Crh1p and Crh2p are the first proteins
directly implicated in the formation of cross-links between cell wall components in fungi
- id: PMID:18694928
title: >-
Assembly of the yeast cell wall. Crh1p and Crh2p act as transglycosylases in vivo and
in vitro.
findings:
- statement: >-
CRH1 and CRH2 act as transglycosylases in vivo and in vitro, transferring chitin chains
to beta(1-6)glucan. High activity at bud scars. Demonstrated using fluorescent acceptors
in intact cells, permeabilized cells, and isolated cell walls.
supporting_text: >-
the Crh proteins act by transferring chitin chains to beta(1-6)glucan, with a newly
observed high activity in the bud scar. The importance of transglycosylation for cell
wall assembly is thus firmly established
- id: PMID:19734368
title: >-
Two novel techniques for determination of polysaccharide cross-links show that Crh1p and
Crh2p attach chitin to both beta(1-6)- and beta(1-3)glucan in the Saccharomyces cerevisiae
cell wall.
findings:
- statement: >-
CRH1 and CRH2 catalyze transfer of chitin to both beta(1-3)- and beta(1-6)-glucan.
All chitin in crh1/crh2 double mutant is free (unlinked). Previous apparent residual
beta(1-3)glucan-linked chitin was an artifact of chitinase contamination in zymolyase.
supporting_text: >-
Crh1p and Crh2p catalyze the transfer of chitin to both beta(1-3)- and beta(1-6)glucan,
and the biosynthetic mechanism for all chitin cross-links in the cell wall has been
established
- id: PMID:23919454
title: >-
A novel fluorescence assay and catalytic properties of Crh1 and Crh2 yeast cell wall
transglycosylases.
findings:
- statement: >-
Heterologously expressed CRH1 and CRH2 act as chitin transglycosylases. Both also have
weak endochitinase activity. pH optimum 3.5, temperature optimum 37C. Minimal acceptor
requires 2 hexopyranose units.
supporting_text: >-
Both proteins act as chitin transglycosylases; they use soluble chitin derivatives, such
as carboxymethyl chitin, glycol-chitin and/or N-acetyl chito-oligosaccharides of
DP (degree of polymerization)≥5 as the oligoglycosyl donors...Both proteins exhibited
a weak chitinolytic activity
- id: PMID:26928762
title: >-
One library to make them all: streamlining the creation of yeast libraries via a SWAp-Tag
strategy.
findings:
- statement: >-
High-throughput SWAp-Tag localization study that assigned CRH1 to cell periphery.
supporting_text: >-
we constructed and investigated a library of ∼1,800 strains carrying SWAT-GFP modules
at the amino termini of endomembrane proteins
suggested_questions:
- question: >-
Is there a more specific GO term for chitin transglycosylase activity that could
distinguish the primary transglycosylation function from the secondary endochitinase
activity? Currently both activities are annotated under different parent terms
(glycosyltransferase vs endochitinase), but there is no specific "chitin
transglycosylase activity" term in GO.
- question: >-
What is the relative in vivo contribution of the endochitinase activity versus the
transglycosylase activity of CRH1? Is the chitinase activity biologically relevant
or simply a side reaction of the GH16 catalytic mechanism?
suggested_experiments:
- hypothesis: >-
CRH1 chitin transglycosylase activity may have distinct substrate preferences in
different cell wall compartments (bud scar vs lateral wall vs septum).
description: >-
Use compartment-specific fluorescent chitin acceptors with conditional CRH1 expression
to determine whether transglycosylation rates differ at different cell surface locations.
Compare with CRH2 localization and activity patterns.
experiment_type: fluorescence microscopy with functional assay