CbpA is the primary cellulosomal scaffoldin of Clostridium cellulovorans, a large non-catalytic protein (~1,848 aa) that serves as the organizational backbone for the cellulosome multi-enzyme complex. The protein contains an N-terminal signal peptide for secretion, one CBM3 (carbohydrate-binding module family 3) that binds crystalline cellulose, four X2 hydrophilic modules, and nine type I cohesin domains that recruit dockerin-bearing cellulolytic enzymes. CbpA targets the cellulosome to cellulose substrates and organizes multiple enzymes (endoglucanases, exoglucanases, xylanases) into a highly efficient degradative complex.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000272 polysaccharide catabolic process | IEA GO_REF:0000120 | MARK AS OVER ANNOTATED | Summary: This annotation is misleading for CbpA. CbpA is a non-catalytic scaffoldin that organizes enzymes but does not itself catalyze polysaccharide catabolism. The cellulosome complex as a whole participates in this process, but attributing it to the scaffoldin alone misrepresents its role. Reason: CbpA is a structural/organizational protein, not a catalytic enzyme. While it enables polysaccharide catabolism by organizing enzymes, it does not directly participate in the catabolic reaction. Supporting Evidence: file:CLOCL/P38058/P38058-deep-research-falcon.md CbpA is the primary non-catalytic backbone of the C. cellulovorans cellulosome |
| GO:0005576 extracellular region | IEA GO_REF:0000044 | ACCEPT | Summary: This annotation is correct. CbpA contains an N-terminal signal peptide (residues 1-28) and is secreted to the extracellular space where it assembles into the cellulosome complex. It remains associated with the cell surface. Reason: UniProt clearly documents the signal peptide and states "Secreted. Note=Remains at the cell surface." The literature confirms CbpA functions extracellularly. Supporting Evidence: file:CLOCL/P38058/P38058-deep-research-falcon.md CbpA contains a Sec-type signal peptide and is secreted, assembling into an extracellular cellulosome |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: This annotation is too general and misrepresents CbpA's role. CbpA does not metabolize carbohydrates; it organizes enzymes that do. This is an overly broad annotation derived from domain composition. Reason: CbpA is non-catalytic. It facilitates carbohydrate metabolism by organizing catalytic enzymes, but does not itself perform any metabolic reaction. Supporting Evidence: file:CLOCL/P38058/P38058-deep-research-falcon.md CbpA is the primary non-catalytic backbone of the C. cellulovorans cellulosome |
| GO:0030245 cellulose catabolic process | IEA GO_REF:0000043 | MARK AS OVER ANNOTATED | Summary: This annotation is misleading. CbpA itself does not catabolize cellulose. It organizes the cellulosome to facilitate cellulose catabolism by the assembled enzymes, but the scaffoldin has no catalytic activity. Reason: As a non-catalytic scaffoldin, CbpA enables but does not directly perform cellulose catabolism. The annotation should be on the catalytic enzymes, not the scaffoldin. Supporting Evidence: file:CLOCL/P38058/P38058-deep-research-falcon.md CbpA is the primary non-catalytic backbone of the C. cellulovorans cellulosome |
| GO:0030246 carbohydrate binding | IEA GO_REF:0000002 | ACCEPT | Summary: This annotation is correct. CbpA contains a CBM3 domain that binds carbohydrates, specifically crystalline cellulose. GO:0030248 (cellulose binding) would be more precise. Reason: The CBM3 domain mediates carbohydrate binding. This is a true positive but could be made more specific with GO:0030248. Supporting Evidence: file:CLOCL/P38058/P38058-deep-research-falcon.md The CBM3 mediates binding of the assembled complex to crystalline cellulose |
| GO:0030248 cellulose binding | IEA GO_REF:0000002 | ACCEPT | Summary: This annotation is correct and represents a core molecular function of CbpA. The CBM3 domain specifically binds crystalline cellulose, targeting the cellulosome to its substrate. Reason: Cellulose binding via CBM3 is a well-characterized function of CbpA, demonstrated experimentally. This is essential for targeting the cellulosome to substrate. Supporting Evidence: file:CLOCL/P38058/P38058-deep-research-falcon.md The CBM3 mediates binding of the assembled complex to crystalline cellulose, increasing local enzyme concentration at the substrate |
| GO:0071555 cell wall organization | IEA GO_REF:0000043 | REMOVE | Summary: This annotation is incorrect. CbpA is involved in degrading plant cell walls (as a target substrate), not in bacterial cell wall organization. The UniProt keyword mapping appears to have conflated cell wall degradation with cell wall organization. Reason: GO:0071555 refers to organization of the organism's own cell wall. CbpA is involved in degrading external plant cell wall material, which is a different process. Supporting Evidence: file:CLOCL/P38058/P38058-deep-research-falcon.md CbpA ... creates a multienzyme complex that acts on plant cell wall polysaccharides |
| GO:0043263 cellulosome | TAS file:CLOCL/P38058/P38058-deep-research-falcon.md | NEW | Summary: CbpA is the primary structural component of the cellulosome. This cellular component annotation is essential for understanding CbpA's identity. Reason: CbpA IS the cellulosome scaffold. It is the primary scaffoldin that organizes the C. cellulovorans cellulosome complex. This annotation is critical. Supporting Evidence: file:CLOCL/P38058/P38058-deep-research-falcon.md CbpA is the primary non-catalytic backbone of the C. cellulovorans cellulosome |
| GO:0044575 cellulosome assembly | TAS file:CLOCL/P38058/P38058-deep-research-falcon.md | NEW | Summary: CbpA's primary biological process is assembling the cellulosome by recruiting dockerin-bearing enzymes via its nine cohesin domains. Reason: CbpA assembles the cellulosome complex through cohesin-dockerin interactions. This is the primary biological process for this scaffoldin protein. Supporting Evidence: file:CLOCL/P38058/P38058-deep-research-falcon.md It recruits dockerin-bearing enzymes (endoglucanases, exoglucanases, xylanases, etc.) via high-specificity cohesin–dockerin interactions |
| GO:1990308 type-I dockerin domain binding | TAS file:CLOCL/P38058/P38058-deep-research-falcon.md | NEW | Summary: CbpA contains nine type I cohesin domains that bind type I dockerins on cellulolytic enzymes. This is the primary molecular mechanism by which CbpA recruits enzymes. Reason: The cohesin-dockerin interaction is central to CbpA function. Nine cohesins provide the binding sites for dockerin-bearing enzymes. Supporting Evidence: file:CLOCL/P38058/P38058-deep-research-falcon.md nine cohesin repeats (type I cohesins) that recruit dockerin-bearing enzymatic subunits |
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Download this section (compressed HTML)Q: What is the binding affinity of each of the nine CbpA cohesin domains for different dockerins?
Q: How does CbpA architecture compare to other clostridial scaffoldins?
Experiment: Quantitative binding assays for each cohesin-dockerin pair to characterize specificity and affinity of CbpA cohesins.
Hypothesis: Different CbpA cohesins may have variable affinities for different dockerin-bearing enzymes, enabling preferential recruitment of certain enzymes.
Experiment: Structural characterization of CbpA cohesin domains by X-ray crystallography or cryo-EM to understand binding interfaces.
Hypothesis: Structural data would reveal molecular details of cohesin-dockerin recognition and explain observed binding specificities.
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