CelC (Endoglucanase C) is a glycoside hydrolase family 5 (GH5) enzyme that catalyzes the endohydrolysis of 1,4-beta-D-glucosidic linkages in cellulose, lichenin, and cereal beta-D-glucans (EC 3.2.1.4). CelC is a non-cellulosomal enzyme, lacking a dockerin domain and therefore does not integrate into the cellulosome complex. The 343 amino acid enzyme contains conserved active site residues typical of GH5 family members, with Gln-140 acting as proton donor and Glu-280 as nucleophile. The celC gene is part of a celC-glyR3-licA operon, with transcription regulated by the LacI-family repressor GlyR3, and induced by laminaribiose.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000272 polysaccharide catabolic process | IEA GO_REF:0000120 | ACCEPT | Summary: This is a parent-level biological process term that correctly captures the catabolic activity of CelC. As an endoglucanase that breaks down cellulose (a polysaccharide), CelC is involved in polysaccharide catabolism. However, more specific child terms (GO:0030245 cellulose catabolic process) are also annotated and are more informative. Reason: The annotation is accurate as cellulose is a polysaccharide and CelC participates in its degradation. This parent term complements the more specific cellulose catabolic process annotation. IEA evidence from InterPro domain and UniProtKB keyword mappings is appropriate for this general term. |
| GO:0004553 hydrolase activity, hydrolyzing O-glycosyl compounds | IEA GO_REF:0000002 | ACCEPT | Summary: This molecular function term is a parent term of cellulase activity (GO:0008810). It accurately describes the general catalytic mechanism of CelC, which hydrolyzes O-glycosyl bonds in cellulose. Reason: As a GH5 family endoglucanase, CelC hydrolyzes O-glycosyl compounds (specifically beta-1,4-glucosidic bonds). The InterPro-based IEA annotation is accurate. This parent term is retained alongside the more specific cellulase activity term. |
| GO:0005576 extracellular region | IEA GO_REF:0000118 | ACCEPT | Summary: CelC is classified as a non-cellulosomal enzyme that functions extracellularly. Deep research confirms CelC acts as a free extracellular enzyme rather than as part of the cellulosome complex [file:ACET2/celC/celC-deep-research-falcon.md]. Reason: Deep research supports extracellular localization. Non-cellulosomal hydrolytic enzymes in C. thermocellum function extracellularly in the milieu of plant biomass. While a signal peptide for CelC is expected for secretion, regulatory and operon studies explicitly classify CelC as non-cellulosomal, implying extracellular action as a free enzyme [file:ACET2/celC/celC-deep-research-falcon.md]. Supporting Evidence: file:ACET2/celC/celC-deep-research-falcon.md Non-cellulosomal hydrolytic enzymes in C. thermocellum function extracellularly in the milieu of plant biomass |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000002 | ACCEPT | Summary: This is a high-level biological process term that accurately but very broadly describes CelC function. The enzyme participates in carbohydrate metabolism through cellulose degradation. Reason: While very general, this annotation is not incorrect. CelC is involved in carbohydrate metabolism via its cellulolytic activity. More specific child terms (cellulose catabolic process) provide better functional resolution. IEA from InterPro is reasonable for this broad term. |
| GO:0008422 beta-glucosidase activity | IEA GO_REF:0000118 | REMOVE | Summary: Beta-glucosidase activity (GO:0008422) is defined as catalysis of hydrolysis of terminal, non-reducing beta-D-glucose residues with release of beta-D-glucose. This is mechanistically distinct from cellulase/endoglucanase activity, which cleaves internal beta-1,4-glucosidic bonds. CelC is an ENDOglucanase, not an EXO-acting beta-glucosidase. Reason: This annotation is incorrect. CelC (EC 3.2.1.4) is an endoglucanase that cleaves internal beta-1,4-glucosidic linkages in cellulose chains. Beta-glucosidase (EC 3.2.1.21) is a distinct enzyme class that removes terminal glucose residues. The TreeGrafter prediction appears to be based on broad sequence similarity within glycoside hydrolases but does not accurately reflect the specific enzymatic mechanism of CelC. UniProt clearly annotates CelC with EC 3.2.1.4 (cellulase), not EC 3.2.1.21 (beta-glucosidase). |
| GO:0008810 cellulase activity | IEA GO_REF:0000003 | ACCEPT | Summary: Cellulase activity (GO:0008810) is defined as catalysis of the endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans. This precisely matches the function of CelC as described in UniProt and confirmed by deep research [file:ACET2/celC/celC-deep-research-falcon.md]. Reason: This is the core molecular function annotation for CelC and is correctly assigned based on EC number mapping (EC:3.2.1.4). UniProt explicitly states that CelC catalyzes endohydrolysis of 1,4-beta-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans. The GH5 family classification and conserved active site residues (Gln-140 proton donor, Glu-280 nucleophile) support this annotation. Supporting Evidence: file:ACET2/celC/celC-deep-research-falcon.md CelC is an endo-1,4-beta-glucanase that cleaves internal beta-1,4-glycosidic bonds in cellulose and related beta-glucans |
| GO:0009251 glucan catabolic process | IEA GO_REF:0000118 | ACCEPT | Summary: Glucan catabolic process is a biological process term that describes the breakdown of glucans. Cellulose is a beta-1,4-glucan, so CelC participates in glucan catabolism through its cellulolytic activity. Reason: This annotation is accurate. CelC breaks down cellulose, which is a glucan (polymer of glucose). The TreeGrafter annotation correctly infers this biological process from sequence homology to characterized cellulases. |
| GO:0009986 cell surface | IEA GO_REF:0000118 | REMOVE | Summary: Cell surface localization is characteristic of cellulosomal enzymes that attach via dockerin-cohesin interactions. However, CelC (A3DJ77) is explicitly classified as non-cellulosomal and lacks a dockerin domain, meaning it cannot attach to the CipA scaffoldin on the cell surface [file:ACET2/celC/celC-deep-research-falcon.md]. Reason: This annotation is incorrect for CelC. Deep research explicitly states that CelC is categorized as non-cellulosomal and acts as a free enzyme rather than a CipA-bound cellulosomal subunit. Regulatory and operon studies explicitly classify CelC as non-cellulosomal, implying absence of a dockerin module. Without a dockerin, CelC cannot bind to the CipA scaffoldin and would not be retained at the cell surface. CelC functions as a free extracellular enzyme, not a cell-surface-attached one. Supporting Evidence: file:ACET2/celC/celC-deep-research-falcon.md CelC is categorized as non-cellulosomal in transcriptional/regulatory studies rather than a dockerin-bearing component file:ACET2/celC/celC-deep-research-falcon.md Regulatory and operon studies explicitly classify CelC as non-cellulosomal; this implies absence of a dockerin module and action as a free enzyme rather than as a CipA-bound cellulosomal subunit |
| GO:0016787 hydrolase activity | IEA GO_REF:0000043 | ACCEPT | Summary: Hydrolase activity is a very broad molecular function term that encompasses all enzymes that catalyze hydrolysis reactions. CelC is a hydrolase that cleaves glycosidic bonds. Reason: This annotation is correct but very general. CelC is indeed a hydrolase (it catalyzes hydrolysis of beta-1,4-glucosidic bonds). The annotation derives from UniProtKB keyword mapping. More specific child terms provide better functional characterization. |
| GO:0016798 hydrolase activity, acting on glycosyl bonds | IEA GO_REF:0000043 | ACCEPT | Summary: This molecular function term specifies that CelC acts on glycosyl bonds, which is accurate. It is a parent term of cellulase activity. Reason: CelC hydrolyzes glycosidic (glycosyl) bonds, specifically beta-1,4-glucosidic linkages. This annotation from UniProtKB keyword mapping correctly places CelC within the glycoside hydrolase functional category. |
| GO:0030245 cellulose catabolic process | IEA GO_REF:0000120 | ACCEPT | Summary: Cellulose catabolic process is the most specific and appropriate biological process term for CelC. It directly describes the enzyme's participation in cellulose degradation. Reason: This is the core biological process annotation for CelC. As an endoglucanase that cleaves internal bonds in cellulose chains, CelC directly participates in cellulose catabolism. UniProt explicitly annotates CelC for the cellulose degradation pathway (UniPathway:UPA00696). This annotation is supported by both the EC number mapping and the UniProt pathway annotation. Supporting Evidence: UniProt:A3DJ77 Glycan metabolism; cellulose degradation |
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Download this section (compressed HTML)Q: What is the specific substrate preference of CelC - does it have higher activity on cellulose, lichenan, or mixed-linkage beta-glucans?
Q: Are there kinetic parameters (Km, kcat) available for purified CelC on carboxymethylcellulose or other defined substrates?
Experiment: Express recombinant A3DJ77 CelC and assay for endoglucanase activity using carboxymethyl cellulose (CMC) or other cellulosic substrates. Demonstration of endoglucanase activity would confirm the GO:0008810 annotation with experimental evidence.
Experiment: Test A3DJ77 CelC for beta-glucosidase activity using p-nitrophenyl-beta-D-glucoside as substrate. Lack of activity would support removal of the GO:0008422 annotation and confirm that CelC is strictly an endoglucanase.
Experiment: Perform substrate specificity profiling to determine whether CelC has preference for cellulose versus lichenan or other beta-glucans, given the operon context with licA and laminaribiose-mediated induction.
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