Endoglucanase D (CelD) is a glycoside hydrolase family 9 (GH9) 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). The enzyme is a component of the Acetivibrio thermocellus cellulosome, a large extracellular multi-enzyme complex that efficiently degrades crystalline cellulose. CelD contains a C-terminal type I dockerin domain (residues 579-649) that mediates binding to type I cohesin domains on the scaffoldin protein CipA, enabling incorporation into the cellulosome. The enzyme requires Ca2+ as a cofactor. The dockerin domain contains two EF-hand calcium-binding motifs that are essential for the calcium-dependent cohesin-dockerin interaction. CelD is secreted via a signal peptide (residues 1-41) and functions extracellularly as part of the cellulosome complex anchored to the bacterial cell surface.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000272 polysaccharide catabolic process | IEA GO_REF:0000120 | MARK AS OVER ANNOTATED | Summary: This annotation is derived from InterPro domain mappings (IPR002105 Dockerin, IPR016134 Dockerin domain, IPR036439 Dockerin domain superfamily). While CelD does participate in polysaccharide catabolism, this term is overly broad for an enzyme with well-characterized cellulose-specific activity. The more specific term GO:0030245 'cellulose catabolic process' is already annotated and better captures the function. Deep research confirms CelD is specifically an endo-1,4-beta-glucanase (EC 3.2.1.4) that cleaves internal beta-1,4-glycosidic linkages in cellulose (celD-deep-research-falcon.md). Reason: The term GO:0000272 'polysaccharide catabolic process' is a parent term of GO:0030245 'cellulose catabolic process'. Since CelD is specifically an endoglucanase (EC 3.2.1.4) that acts on cellulose, lichenin, and cereal beta-D-glucans as stated in UniProt, the more specific cellulose catabolic process term is more appropriate. This IEA annotation from InterPro domain mapping is not incorrect but represents an over-annotation when the more specific term is available. Supporting Evidence: file:ACET2/celD/celD-deep-research-falcon.md CelD is an endo-1,4-beta-glucanase (EC 3.2.1.4) that cleaves internal beta-1,4-glycosidic linkages in cellulose and related beta-glucans |
| GO:0004553 hydrolase activity, hydrolyzing O-glycosyl compounds | IEA GO_REF:0000120 | MARK AS OVER ANNOTATED | Summary: This annotation is derived from ARBA rule ARBA00027782 and InterPro domains IPR001701 (Glyco_hydro_9) and IPR002105 (Dockerin). While technically correct as CelD does hydrolyze O-glycosyl compounds, this is an overly general term. The more specific GO:0008810 'cellulase activity' is already annotated and better represents the molecular function. Reason: GO:0004553 'hydrolase activity, hydrolyzing O-glycosyl compounds' is a parent term of GO:0008810 'cellulase activity'. CelD is specifically classified as EC 3.2.1.4 (cellulase/endo-1,4-beta-glucanase) in UniProt with the catalytic activity described as 'Endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans'. The more specific cellulase activity term should be preferred. Supporting Evidence: file:ACET2/celD/celD-deep-research-falcon.md GH9 endoglucanases hydrolyze amorphous cellulose, soluble beta-glucans (e.g., CMC), and contribute to attack on crystalline cellulose |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: This annotation is derived from InterPro2GO mapping based on multiple InterPro domains including IPR001701 (Glyco_hydro_9), IPR004197 (Cellulase_Ig-like), IPR008928 (6-hairpin_glycosidase_sf), and IPR012341 (6hp_glycosidase-like_sf). While correct, this is an extremely broad parent term and the more specific GO:0030245 'cellulose catabolic process' better captures the biological process. Reason: GO:0005975 'carbohydrate metabolic process' is a very high-level term that encompasses essentially all carbohydrate metabolism. CelD functions specifically in cellulose degradation as evidenced by its UniProt keywords (Cellulose degradation, Glycosidase) and EC classification (3.2.1.4). The GO:0030245 'cellulose catabolic process' annotation already present is far more informative and specific. Supporting Evidence: file:ACET2/celD/celD-deep-research-falcon.md CelD (celD; A3DDN1) from C. thermocellum ATCC 27405 is a secreted, cellulosomal GH9 endoglucanase (EC 3.2.1.4) |
| GO:0008810 cellulase activity | IEA GO_REF:0000120 | ACCEPT | Summary: This annotation is derived from InterPro domain IPR004197 (Cellulase_Ig-like) and EC number mapping (EC:3.2.1.4). This is the core molecular function of CelD. The UniProt entry explicitly states EC=3.2.1.4 and describes the catalytic activity as 'Endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans'. CelD belongs to glycosyl hydrolase family 9 (GH9) as indicated by CAZy database cross-reference. Reason: GO:0008810 'cellulase activity' is defined as 'Catalysis of the endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans' which precisely matches the EC 3.2.1.4 classification and catalytic activity description in UniProt for CelD. This is the appropriate molecular function term for an endoglucanase and represents a core function of the protein. Supporting Evidence: UniProt:A3DDN1 Endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans.; EC=3.2.1.4 file:ACET2/celD/celD-deep-research-falcon.md CelD is an endo-1,4-beta-glucanase (EC 3.2.1.4) that cleaves internal beta-1,4-glycosidic linkages in cellulose and related beta-glucans |
| GO:0016787 hydrolase activity | IEA GO_REF:0000043 | MARK AS OVER ANNOTATED | Summary: This annotation is derived from UniProtKB keyword mapping (KW-0378 Hydrolase). While technically correct, this is an extremely broad term. The more specific GO:0008810 'cellulase activity' already annotated provides much more information about the actual molecular function. Reason: GO:0016787 'hydrolase activity' is an ancestor term of GO:0008810 'cellulase activity'. For a well-characterized enzyme with specific substrate preferences like CelD (EC 3.2.1.4), retaining such a general term provides no additional information beyond what the specific cellulase activity term already conveys. Supporting Evidence: file:ACET2/celD/celD-deep-research-falcon.md Glycoside hydrolase family 9 (GH9); endo-1,4-beta-glucanase, EC 3.2.1.4 |
| GO:0016798 hydrolase activity, acting on glycosyl bonds | IEA GO_REF:0000043 | MARK AS OVER ANNOTATED | Summary: This annotation is derived from UniProtKB keyword mapping (KW-0326 Glycosidase). While correct, this term is intermediate in specificity between the overly broad 'hydrolase activity' and the appropriately specific 'cellulase activity'. The cellulase activity term is already present and more informative. Reason: GO:0016798 'hydrolase activity, acting on glycosyl bonds' is a parent term of GO:0008810 'cellulase activity'. Since CelD is specifically classified as a cellulase (EC 3.2.1.4), the more specific term already annotated is preferred and this intermediate term represents redundant annotation. Supporting Evidence: file:ACET2/celD/celD-deep-research-falcon.md CelD is an endo-1,4-beta-glucanase (EC 3.2.1.4) that cleaves internal beta-1,4-glycosidic linkages in cellulose and related beta-glucans |
| GO:0030245 cellulose catabolic process | IEA GO_REF:0000043 | ACCEPT | Summary: This annotation is derived from UniProtKB keyword mapping (KW-0136 Cellulose degradation). This accurately reflects the biological process in which CelD participates. As an endoglucanase (EC 3.2.1.4) that cleaves internal beta-1,4-glucosidic bonds in cellulose, CelD directly contributes to cellulose catabolism within the cellulosome complex. Reason: GO:0030245 'cellulose catabolic process' is the appropriate biological process term for CelD. The UniProt entry lists 'Cellulose degradation' as a keyword and describes the function as catalyzing endohydrolysis of glucosidic linkages in cellulose. This is a core function term representing the primary biological role of this endoglucanase in the A. thermocellus cellulosome. Supporting Evidence: UniProt:A3DDN1 Endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans.; EC=3.2.1.4 file:ACET2/celD/celD-deep-research-falcon.md CelD (celD; A3DDN1) from C. thermocellum ATCC 27405 is a secreted, cellulosomal GH9 endoglucanase (EC 3.2.1.4) that integrates via dockerin-cohesin into the CipA scaffold |
| GO:0043263 cellulosome | ISS UniProt:A3DDN1 | NEW | Summary: This cellular component annotation captures the localization of CelD within the cellulosome complex. CelD contains a type I dockerin domain (residues 579-649) that mediates binding to type I cohesin domains on the scaffoldin CipA. The dockerin domain is annotated in UniProt and literature confirms CelD binding to CipA-derived mini-scaffoldins. Reason: GO:0043263 'cellulosome' is a critical cellular component annotation that is missing from the current GOA annotations. The UniProt entry clearly indicates CelD has a dockerin domain (residues 579-649) that mediates cellulosome incorporation via cohesin-dockerin interactions. The protein is secreted (signal peptide 1-41) and functions as part of the extracellular cellulosome. Deep research confirms CelD binding to CipA-derived constructs. Supporting Evidence: UniProt:A3DDN1 InterPro; IPR002105; Dockerin_1_rpt file:ACET2/celD/celD-deep-research-falcon.md CelD is secreted and functions extracellularly as a cellulosomal component tethered to CipA |
| GO:1990311 type-I cohesin domain binding | ISS UniProt:A3DDN1 | NEW | Summary: CelD contains a type I dockerin domain that specifically binds to type I cohesin domains on scaffoldin proteins like CipA. This molecular function annotation would capture the important cohesin-dockerin interaction that enables cellulosome assembly. The dockerin domain is annotated in UniProt with clear evidence from sequence analysis. Reason: GO:1990311 'type-I cohesin domain binding' precisely describes the molecular function of the dockerin domain present in CelD. The UniProt entry annotates residues 579-649 as a dockerin domain. Type I dockerins bind type I cohesins, which is how CelD is incorporated into the cellulosome via the CipA scaffoldin. This is a significant molecular function that enables the multi-enzyme complex formation essential for efficient cellulose degradation. Supporting Evidence: file:ACET2/celD/celD-deep-research-falcon.md dockerin-bearing enzymes (including CelD) are recruited via cohesin-dockerin binding file:ACET2/celD/celD-deep-research-falcon.md interaction studies demonstrate CelD binding to CipA-derived mini-scaffoldins, confirming a cellulosomal dockerin module |
| GO:0005509 calcium ion binding | ISS UniProt:A3DDN1 | NEW | Summary: CelD requires Ca2+ as a cofactor as stated in UniProt. The dockerin domain contains two EF-hand calcium-binding sites (PROSITE PS00018) that are essential for the calcium-dependent cohesin-dockerin interaction. This molecular function is important for cellulosome assembly. Reason: GO:0005509 'calcium ion binding' is supported by multiple lines of evidence in the UniProt entry. The cofactor annotation explicitly states Ca2+ is required. Additionally, two EF-hand calcium-binding sites are annotated via PROSITE PS00018. The dockerin domain function is calcium-dependent, and calcium binding is essential for the cohesin-dockerin interaction that enables cellulosome assembly. Supporting Evidence: UniProt:A3DDN1 Name=Ca(2+); Xref=ChEBI:CHEBI:29108; Evidence={ECO:0000250} UniProt:A3DDN1 InterPro; IPR018247; EF_Hand_1_Ca_BS |
Loading supporting content…
Download this section (compressed HTML)Q: What is the specific substrate preference of CelD for different beta-glucans (cellulose vs lichenin vs barley beta-glucan)?
Q: What is the synergistic contribution of CelD relative to other cellulosomal endoglucanases?
Q: Are there specific cohesin positions on CipA that preferentially bind CelD?
Experiment: Kinetic characterization of purified CelD with various cellulosic substrates
Hypothesis: CelD has distinct kinetic parameters for cellulose, lichenin, and barley beta-glucan
Experiment: Mutagenesis of dockerin domain calcium-binding residues to confirm calcium dependence
Hypothesis: Calcium binding is essential for cohesin-dockerin interaction
Experiment: Cryo-EM studies of mini-cellulosomes containing CelD to understand spatial arrangement
Hypothesis: CelD adopts a specific orientation when bound to CipA cohesins
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)