CelA (also known as Cel8A or Endoglucanase A) is a secreted endo-beta-1,4-glucanase (EC 3.2.1.4) belonging to glycosyl hydrolase family 8 (GH8). It catalyzes the endohydrolysis of internal (1->4)-beta-D-glucosidic linkages in cellulose, lichenin, and cereal beta-D-glucans. The enzyme contains a GH8 catalytic domain with an open cleft/groove architecture characteristic of endo-acting glycosidases, plus a C-terminal type I dockerin domain (residues 411-477) that mediates incorporation into the cellulosome complex via cohesin-dockerin interactions with the primary scaffoldin CipA. CelA is one of the major catalytic components of the C. thermocellum cellulosome, consistently identified in proteomic surveys of purified cellulosomes grown on Avicel. The enzyme lacks its own carbohydrate-binding module (CBM) and relies on the CBM of CipA for targeting to insoluble cellulose substrates. Structural studies at atomic resolution (0.94 A) have characterized the active site, identifying residues E95 (proton donor) and D152 (nucleophile) as key catalytic residues.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0000272
polysaccharide catabolic process
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: CelA is an endoglucanase that participates in cellulose degradation. While cellulose is a polysaccharide, the more specific term GO:0030245 (cellulose catabolic process) is already annotated and better represents the biological process. This broader term is acceptable but redundant given the more specific annotation. The deep research review confirms CelA's role in cellulose breakdown as part of the cellulosome complex [celA-deep-research-falcon.md].
Reason: This annotation is correct but overly broad. CelA specifically degrades cellulose, which is a type of polysaccharide. The term is inferred from InterPro domain annotations (IPR002105 Dockerin, IPR016134 Dockerin domain, IPR036439 Dockerin superfamily) which correctly associate the protein with polysaccharide degradation. Since GO:0030245 (cellulose catabolic process) is also annotated and is more specific, this broader term is somewhat redundant but not incorrect. For IEA annotations, broader parent terms are acceptable to retain alongside more specific ones.
|
|
GO:0004553
hydrolase activity, hydrolyzing O-glycosyl compounds
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: CelA is a glycosyl hydrolase (GH8 family) that hydrolyzes O-glycosyl compounds, specifically (1->4)-beta-D-glucosidic linkages. This term is correct but a parent of the more specific GO:0008810 (cellulase activity) which is also annotated.
Reason: This annotation is correct. CelA belongs to GH8 and catalyzes hydrolysis of beta-glucosidic bonds in cellulose. The annotation is inferred from ARBA rule ARBA00027782 and InterPro domains IPR002037 (Glyco_hydro_8) and IPR002105 (Dockerin). While GO:0008810 (cellulase activity) is more specific, this parent term is acceptable for an IEA annotation and provides a useful grouping term.
|
|
GO:0005975
carbohydrate metabolic process
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: CelA participates in carbohydrate metabolism through its role in cellulose degradation. This is a high-level parent term of more specific annotations already present.
Reason: This annotation is correct but very broad. It is inferred from InterPro records IPR002037 (Glyco_hydro_8), IPR008928 (6-hairpin_glycosidase_sf), and IPR012341 (6hp_glycosidase-like_sf). While the more specific GO:0030245 (cellulose catabolic process) better captures CelA's function, this broader term is not incorrect and acceptable for an IEA annotation derived from domain membership.
|
|
GO:0008810
cellulase activity
|
IEA
GO_REF:0000003 |
ACCEPT |
Summary: CelA (Endoglucanase A) is definitively a cellulase with EC 3.2.1.4 activity. It catalyzes the endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin, and cereal beta-D-glucans. This is the core molecular function of the enzyme and the most specific appropriate MF term.
Reason: This annotation accurately represents the core molecular function of CelA. The enzyme is explicitly annotated as EC 3.2.1.4 (endoglucanase/cellulase) in UniProt, and the GO term definition matches exactly: "Catalysis of the endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans." The annotation is derived from the EC number mapping (GO_REF:0000003). Proteomic studies identify CelA/Cel8A as a major catalytic component of the cellulosome with endo-beta-1,4-glucanase activity [PMID:16127726, PMID:17644599]. Structural studies confirm the open cleft architecture characteristic of endo-acting glycosidases [PMID:8805535].
Supporting Evidence:
PMID:16127726
Ten of the components were previously known: the structural protein CipA, the endo-glucanases Cel8A, Cel5G, Cel9N, the cellobiohydrolases Cbh9A, Cel9K, Cel48S, the xylanases Xyn10C, Xyn10Z, and the chitinase Chi18A
PMID:17644599
In total, 41 cellulosomal proteins were detected, including 36 type I dockerin-containing proteins
|
|
GO:0016787
hydrolase activity
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: CelA is a hydrolase that cleaves glycosidic bonds. This is a very broad parent term of the more specific cellulase activity already annotated.
Reason: This annotation is correct but extremely broad. CelA is indeed a hydrolase (EC 3.2.1.4), but the term GO:0008810 (cellulase activity) provides much more informative functional information. This IEA annotation derived from UniProtKB keyword KW-0378 (Hydrolase) is acceptable but provides minimal functional insight beyond what is captured by more specific terms.
|
|
GO:0016798
hydrolase activity, acting on glycosyl bonds
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: CelA hydrolyzes glycosyl bonds, specifically (1->4)-beta-D-glucosidic linkages. This term is a parent of GO:0004553 (hydrolase activity, hydrolyzing O-glycosyl compounds) and GO:0008810 (cellulase activity).
Reason: This annotation is correct. CelA acts on glycosyl bonds (specifically beta-1,4 glucosidic bonds in cellulose). The annotation is inferred from UniProtKB keyword KW-0326 (Glycosidase). While more specific terms are available and already annotated, this intermediate-level term is acceptable for an IEA.
|
|
GO:0030245
cellulose catabolic process
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: CelA is a cellulose-degrading endoglucanase that directly participates in cellulose catabolism as part of the cellulosome complex. This is the appropriate biological process term for this enzyme.
Reason: This annotation accurately represents CelA's biological role. The enzyme catalyzes the endohydrolysis of cellulose chains, producing new chain ends for exoglucanases and contributing directly to cellulose breakdown. The annotation is derived from UniProtKB keyword KW-0136 (Cellulose degradation). Proteomic analyses confirm CelA is a major component of the cellulosome, the multi-enzyme complex responsible for cellulose catabolism in C. thermocellum [PMID:16127726, PMID:17644599, PMID:38234915].
Supporting Evidence:
PMID:38234915
the anchoring of various cellulolytic enzymes, i.e., endoglucanases, cellobiohydrolases, xylanases, to a scaffoldin makes it a complex structure in which different enzymes work synergistically to attack heterogeneous, insoluble cellulose substrates
file:ACET2/celA/celA-deep-research-falcon.md
CelA/Cel8A is an endo-beta-1,4-glucanase (EC 3.2.1.4) that cleaves internal bonds in cellulose chains, producing new chain ends for exoglucanases
|
|
GO:0043263
cellulosome
|
IEA
GO_REF:0000120 |
NEW |
Summary: CelA contains a type I dockerin domain that mediates its incorporation into the cellulosome complex. The cellulosome (GO:0043263) is the appropriate cellular component annotation for this protein.
Reason: CelA has a well-characterized dockerin domain (residues 411-477) that binds to type I cohesins on the CipA scaffoldin. Proteomic surveys consistently identify CelA as a component of purified cellulosomes. This cellular component annotation should be added, as the protein functions as part of the cellulosome complex. The InterPro domains IPR002105 (Dockerin_1_rpt), IPR016134 (Dockerin_dom), and IPR036439 (Dockerin_dom_sf) all indicate cellulosome localization. Note: This annotation may already exist via IEA but was not present in the provided GOA file.
Proposed replacements:
cellulosome
Supporting Evidence:
PMID:16127726
To identify the predominant catalytic components, cellulosomes were purified and the components were separated by an adapted two-dimensional gel electrophoresis technique. The apparent major spots were identified by MALDI-TOF/TOF
PMID:38234915
Cellulosome comprises two major subunits: long flexible scaffoldin, which forms the center part containing specific binding sites cohesions, and the enzymes containing a dockerin module that binds to cohesion
|
Q: What is the precise substrate specificity of CelA compared to other GH8 endoglucanases in the cellulosome? Does it show any preference for specific regions of crystalline vs amorphous cellulose?
Q: How does CelA synergize with exoglucanases (like CelS/Cel48A) and other endoglucanases in the cellulosome to achieve efficient cellulose degradation?
Experiment: Compare the kinetic parameters (kcat, Km) of CelA in free form versus when bound to mini-cellulosomes containing different combinations of other cellulases. Use defined cellulose substrates (Avicel, filter paper, CMC, phosphoric acid swollen cellulose) to assess potential synergistic effects.
Hypothesis: CelA shows optimal activity when incorporated into the cellulosome complex compared to free enzyme, due to proximity effects with other cellulases.
Type: enzyme kinetics
provider: falcon
model: Edison Scientific Literature
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start_time: '2025-12-26T17:03:11.950390'
end_time: '2025-12-26T17:08:34.462065'
duration_seconds: 322.51
template_file: templates/gene_research_go_focused.md
template_variables:
organism: ACET2
gene_id: celA
gene_symbol: celA
uniprot_accession: A3DC29
protein_description: 'RecName: Full=Endoglucanase A; Short=EGA; EC=3.2.1.4; AltName:
Full=Cellulase A; AltName: Full=Endo-1,4-beta-glucanase; Flags: Precursor;'
gene_info: Name=celA; OrderedLocusNames=Cthe_0269;
organism_full: Acetivibrio thermocellus (strain ATCC 27405 / DSM 1237 / JCM 9322
/ NBRC 103400 / NCIMB 10682 / NRRL B-4536 / VPI 7372) (Clostridium thermocellum).
protein_family: Belongs to the glycosyl hydrolase 8 (cellulase D) family.
protein_domains: 6-hairpin_glycosidase_sf. (IPR008928); 6hp_glycosidase-like_sf.
(IPR012341); Dockerin_1_rpt. (IPR002105); Dockerin_dom. (IPR016134); Dockerin_dom_sf.
(IPR036439)
provider_config:
timeout: 600
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parameters:
allowed_domains: []
temperature: 0.1
citation_count: 11
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 'celA' 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 celA (gene ID: celA, UniProt: A3DC29) 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 'celA' 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 celA (gene ID: celA, UniProt: A3DC29) 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 verification: The target is celA (also called Cel8A/Endoglucanase A), a glycoside hydrolase family 8 (GH8) enzyme from Acetivibrio thermocellus (formerly Clostridium thermocellum). In classical proteomics of purified C. thermocellum cellulosomes, CelA/Cel8A is explicitly identified as an endoglucanase and listed among the major catalytic components; domain annotation in those datasets is GH8 with a type I dockerin (GH8-Doc1), consistent with the UniProt A3DC29 record listing an endoglucanase with dockerin motifs in a GH8 fold. Organism is correct for those identifications (C. thermocellum, synonymous with A. thermocellus). The symbol “celA” is potentially ambiguous across species; here we restrict all claims to C. thermocellum/A. thermocellus CelA/Cel8A as supported by cited sources (zverlov2005functionalsubgenomicsof pages 1-2, zverlov2005functionalsubgenomicsof pages 2-4, gold2007globalviewof pages 2-3, datta2024enzymaticdegradationof pages 10-12).
Comprehensive research report
1) Key concepts and definitions
- Protein/gene: celA (Cel8A; Endoglucanase A) encodes a modular, extracellular cellulase deployed within the C. thermocellum/A. thermocellus cellulosome. It belongs to GH family 8 and carries a type I dockerin for incorporation into the primary scaffoldin CipA through cohesin–dockerin interactions (notation GH8-Doc1). Proteomic analyses of purified cellulosomes identify CelA/Cel8A among the major catalytic subunits under cellulose growth (Avicel) (zverlov2005functionalsubgenomicsof pages 2-4, zverlov2005functionalsubgenomicsof pages 1-2, gold2007globalviewof pages 2-3).
- Catalytic activity: Endo-β-1,4-glucanase (EC 3.2.1.4), which cleaves internal β-1,4-glycosidic bonds along cellulose chains; structural descriptions highlight an open cleft/groove at the active site, consistent with endo-acting specificity (bras2012structureandfunction pages 56-59).
- Cellulosome context: The cellulosome is a supramolecular extracellular complex anchored to the cell surface via scaffoldin modules. CipA carries multiple type I cohesins for enzymatic dockerins and a type II dockerin for cell-surface anchoring, together with a CBM that targets insoluble cellulose, enabling synergistic action of endoglucanases, exoglucanases, and hemicellulases (datta2024enzymaticdegradationof pages 10-12).
2) Recent developments and latest research (2023–2024 prioritized)
- Current perspective: 2024 review articles reiterate that much modern understanding of cellulosome architecture and enzyme synergy derives from C. thermocellum; these reviews emphasize cohesin–dockerin specificity, scaffoldin architecture, and the advantage of multi-enzyme colocalization for crystalline cellulose depolymerization. They also underscore cellulosome engineering and designer cellulosomes for biomass conversion as active directions (datta2024enzymaticdegradationof pages 10-12). While this recent literature discusses the C. thermocellum cellulosome broadly, it does not present new CelA-specific kinetics; instead, it consolidates the role of CelA/Cel8A as a cellulosomal endoglucanase in the canonical complex.
3) Current applications and real-world implementations
- Biomass conversion: The cellulosome’s architecture—CBM-mediated substrate targeting and synergistic arrays of catalytic subunits—serves as a template for industrial enzyme cocktails and designer cellulosomes aimed at enhancing saccharification efficiency. The 2024 synthesis emphasizes that cellulosome-inspired designs can outperform free enzyme systems due to proximity and coordinated action, a concept derived largely from studies of C. thermocellum (datta2024enzymaticdegradationof pages 10-12).
4) Expert opinions and analysis from authoritative sources
- Major-component status: Proteomic cataloging established CelA/Cel8A among the prominent catalytic constituents of the native cellulosome, supporting its central role in cellulose deconstruction. Zverlov et al. identified Cel8A within a set of 13 major extracellular catalytic components; Gold and Martin quantified its presence in Avicel-grown cellulosomes, reinforcing its importance (zverlov2005functionalsubgenomicsof pages 1-2, gold2007globalviewof pages 2-3).
- Structural-functional insights: Structural characterization of Cel8A’s endo-acting cleft and arrangements on mini-cellulosomes—three Cel8A enzymes bound to consecutive cohesins, projecting catalytic domains antiparallel—offers a mechanistic rationale for enhanced substrate accessibility within scaffoldin arrays (bras2012structureandfunction pages 56-59). These observations support the design principle that specific spatial arrangements and relative rigidity of linkers can modulate enzymatic synergy.
5) Relevant statistics and data from recent and foundational studies
- Proteomic quantitation: In quantitative proteomics of purified cellulosomes from Avicel-grown cultures, CelA was identified with 14 unique peptides and an emPAI value of 2.46, indicating substantive abundance in the complex under these conditions. Cellulosomes were affinity-purified and analyzed by LC-MS with 15N metabolic labeling for quantitation (gold2007globalviewof pages 2-3). Earlier proteomics also listed Cel8A as one of 13 major catalytic components of the cellulosome prepared from cellulose-grown cultures (zverlov2005functionalsubgenomicsof pages 1-2).
- Domain annotation and size: CelA/Cel8A is annotated as GH8-Doc1 (GH8 catalytic domain plus type I dockerin) with an approximate molecular mass near 53 kDa in proteomic tables (zverlov2005functionalsubgenomicsof pages 2-4).
Functional annotation of celA (Cel8A) in A. thermocellus
- Primary function and substrate specificity: CelA/Cel8A is an endo-β-1,4-glucanase (EC 3.2.1.4) that cleaves internal bonds in cellulose chains, producing new chain ends for exoglucanases. Structural evidence shows a groove/open cleft typical of endo-acting enzymes (bras2012structureandfunction pages 56-59, datta2024enzymaticdegradationof pages 10-12).
- Domain architecture: GH8 catalytic module fused to a type I dockerin (GH8-Doc1). The dockerin targets type I cohesins on the primary scaffoldin CipA; in cellulosomal particles, CelA lacks its own CBM and relies on CipA’s CBM for cellulose targeting. Reported proteomic mass for CelA is ~53 kDa (zverlov2005functionalsubgenomicsof pages 2-4, datta2024enzymaticdegradationof pages 10-12).
- Localization and complex assembly: CelA is secreted and incorporated into the extracellular cellulosome via dockerin–cohesin binding to CipA. The cellulosome is subsequently anchored to the cell surface via type II cohesin–dockerin interactions with anchoring scaffoldins; CipA’s CBM binds crystalline cellulose, positioning CelA for action in a synergistic enzyme array (datta2024enzymaticdegradationof pages 10-12, zverlov2005functionalsubgenomicsof pages 1-2, gold2007globalviewof pages 2-3).
- Evidence for prominence: CelA is consistently detected as a significant component of the C. thermocellum cellulosome in proteomic surveys—both as a major component (Zverlov et al.) and with quantifiable abundance (14 peptides; emPAI 2.46) under Avicel growth (Gold and Martin), supporting a primary role in cellulose deconstruction (zverlov2005functionalsubgenomicsof pages 1-2, gold2007globalviewof pages 2-3).
- Structural/assembly insights: Mini-cellulosome studies show multiple Cel8A catalytic cores bound on consecutive cohesins with antiparallel orientation, and a relatively rigid inter-domain linker, offering a physical basis for enhanced surface coverage and catalytic synergy on insoluble substrates (bras2012structureandfunction pages 56-59).
Limitations and open points
- Kinetic parameters: Specific kcat, Km, and product profiles for A. thermocellus CelA/Cel8A were not reported in the recent 2023–2024 sources here; quantitative kinetics for this precise isozyme were not present in the retrieved excerpts and remain to be detailed from primary enzymology studies (datta2024enzymaticdegradationof pages 10-12).
Embedded summary table
| Attribute | Evidence-based summary | Organism / Strain | Domain architecture | Function / EC | Substrate specificity | Localization / complex | Evidence of abundance (quant.) | Notable structural / assembly insights | Recent 2023–2024 context |
|---|---|---|---|---|---|---|---:|---|---|
| Name / synonyms | Listed as CelA (also called Cel8A / Endoglucanase A) among major cellulosomal components (identified in purified cellulosome proteome) (zverlov2005functionalsubgenomicsof pages 1-2, zverlov2005functionalsubgenomicsof pages 2-4) | Clostridium thermocellum (Acetivibrio thermocellus) (zverlov2005functionalsubgenomicsof pages 1-2, gold2007globalviewof pages 2-3) | — | — | — | — | — | — | — |
| Organism / Strain | Component of the C. thermocellum cellulosome; identified from cellulose-grown cultures (zverlov2005functionalsubgenomicsof pages 1-2, gold2007globalviewof pages 2-3) | Clostridium thermocellum (Acetivibrio thermocellus) (zverlov2005functionalsubgenomicsof pages 1-2) | — | — | — | — | — | — | — |
| Domain architecture | Annotated as GH8 catalytic module plus a type-I dockerin (notation: GH8-Doc1); module analysis based on genome/proteome ORF annotation (zverlov2005functionalsubgenomicsof pages 2-4) | C. thermocellum (zverlov2005functionalsubgenomicsof pages 2-4) | GH8 catalytic domain + Type I dockerin (GH8-Doc1) (zverlov2005functionalsubgenomicsof pages 2-4) | — | — | — | — | — | — |
| Molecular mass | Reported approximate mass ~53 kDa in proteomic table (zverlov2005functionalsubgenomicsof pages 2-4) | C. thermocellum (zverlov2005functionalsubgenomicsof pages 2-4) | GH8-Doc1 architecture consistent with ~53 kDa species (zverlov2005functionalsubgenomicsof pages 2-4) | — | — | — | — | — | — |
| Catalytic function (EC) | Described as an endo-β-1,4-glucanase (endo-activity consistent with EC 3.2.1.4) based on structural/functional description (bras2012structureandfunction pages 56-59) | C. thermocellum (bras2012structureandfunction pages 56-59) | GH8 (endo-β-1,4-glucanase) module (bras2012structureandfunction pages 56-59) | Endo-β-1,4-glucanase (EC 3.2.1.4) — described in literature (bras2012structureandfunction pages 56-59) | Cleaves internal β-1,4 glycosidic bonds in cellulose (endo-activity) (bras2012structureandfunction pages 56-59) | Cellulosomal enzyme (extracellular, scaffoldin-bound) (datta2024enzymaticdegradationof pages 10-12, zverlov2005functionalsubgenomicsof pages 1-2) | — | Groove-shaped binding region and open cleft consistent with endo action (structural description) (bras2012structureandfunction pages 56-59) | Reviews and analyses of cellulosome architecture and enzyme synergy remain active (general 2024 review context) (datta2024enzymaticdegradationof pages 10-12) |
| Substrate specificity | Inferred/observed endo-acting on cellulose (internal chain cleavage); described as endo-β-1,4-glucanase (bras2012structureandfunction pages 56-59) | C. thermocellum (bras2012structureandfunction pages 56-59) | GH8 catalytic signature implies activity on β-1,4-glucans (bras2012structureandfunction pages 56-59) | EC 3.2.1.4 (endo-glucanase) (bras2012structureandfunction pages 56-59) | Internal cleavage of cellulose chains (bras2012structureandfunction pages 56-59) | Functions as part of cellulosome on insoluble cellulose substrates (datta2024enzymaticdegradationof pages 10-12) | — | Endo-type groove and open cleft architecture favor internal bond hydrolysis (bras2012structureandfunction pages 56-59) | Cellulosome synergy (scaffoldin CBM and multi-enzyme arrays) emphasized in recent overviews (datta2024enzymaticdegradationof pages 10-12) |
| Localization / complex | Extracellular, cellulosome-associated enzyme that binds scaffoldin (e.g., CipA) via dockerin–cohesin interactions; isolated from purified cellulosome fractions (datta2024enzymaticdegradationof pages 10-12, zverlov2005functionalsubgenomicsof pages 1-2, gold2007globalviewof pages 2-3) | C. thermocellum (datta2024enzymaticdegradationof pages 10-12, gold2007globalviewof pages 2-3) | Dockerin (type I) mediates Cohesin binding to CipA scaffoldin (zverlov2005functionalsubgenomicsof pages 2-4, datta2024enzymaticdegradationof pages 10-12) | — | Acts on cellulose in cellulosome context (datta2024enzymaticdegradationof pages 10-12) | Localized to extracellular cellulosomal particle; may be positioned by scaffoldin cohesins (datta2024enzymaticdegradationof pages 10-12) | — | Identified in mini‑cellulosome arrangements where multiple Cel8A enzymes bind consecutive cohesins (bras2012structureandfunction pages 56-59) | Cellulosome assembly and anchoring mechanisms remain a focus of recent studies/reviews (datta2024enzymaticdegradationof pages 10-12) |
| Evidence of abundance (proteomics metrics) | Detected in purified Avicel-grown cellulosomes with 14 unique peptides and an emPAI value of 2.46; included among major cellulosomal components (gold2007globalviewof pages 2-3, zverlov2005functionalsubgenomicsof pages 1-2) | C. thermocellum cellulosome (gold2007globalviewof pages 2-3) | — | — | — | Present in extracellular purified cellulosome fraction (gold2007globalviewof pages 2-3) | 14 peptides identified; emPAI = 2.46 (gold2007globalviewof pages 2-3) | Listed among 13 major catalytic components detected in cellulosome proteome (zverlov2005functionalsubgenomicsof pages 1-2) | Proteomic quantification confirms CelA as a substantive component of the cellulosome under cellulose growth (gold2007globalviewof pages 2-3) |
| Notable structural / assembly insights | Structural descriptions: groove-shaped substrate-binding region; in mini-cellulosome three Cel8A enzymes were observed bound to consecutive cohesins, projecting catalytic cores antiparallel to enhance substrate access; linker proposed relatively rigid (bras2012structureandfunction pages 56-59) | C. thermocellum (bras2012structureandfunction pages 56-59) | GH8 catalytic fold with dockerin-mediated attachment (bras2012structureandfunction pages 56-59, zverlov2005functionalsubgenomicsof pages 2-4) | Endo mechanism supported by open cleft/groove architecture (bras2012structureandfunction pages 56-59) | Optimized for internal chain cleavage; spatial arrangement on scaffoldin increases accessibility (bras2012structureandfunction pages 56-59) | Cellulosomal placement (on CipA) positions enzyme for cooperative action (datta2024enzymaticdegradationof pages 10-12, bras2012structureandfunction pages 56-59) | — | Groove/open cleft; antiparallel arrangement when multiple Cel8A bound to consecutive cohesins (bras2012structureandfunction pages 56-59) | Design principles of cellulosomes (multi-enzyme arrays for synergy) are reinforced in recent reviews (datta2024enzymaticdegradationof pages 10-12) |
| Recent 2023–2024 context | No direct new CelA-specific kinetic or expression studies in these contexts; broader 2024 reviews emphasize ongoing work on cellulosome diversity, composition, and engineering for biomass conversion (datta2024enzymaticdegradationof pages 10-12) | C. thermocellum and related Acetivibrio species discussed in genomic and review analyses (datta2024enzymaticdegradationof pages 10-12) | Domain features (dockerin/cohesin interactions) remain central to engineering/design strategies (datta2024enzymaticdegradationof pages 10-12, zverlov2005functionalsubgenomicsof pages 2-4) | — | — | Cellulosome architecture and enzyme complements are active research targets for biofuel/bioprocess applications (datta2024enzymaticdegradationof pages 10-12) | Proteomic identification of CelA in classical studies underpins its inclusion in modern cellulosome models (gold2007globalviewof pages 2-3, zverlov2005functionalsubgenomicsof pages 1-2) | — | Emphasis on exploiting cellulosome enzyme arrays for improved saccharification and synthetic designer cellulosomes in recent reviews (datta2024enzymaticdegradationof pages 10-12) |
Table: Compact, evidence-linked summary of CelA (Cel8A/Endoglucanase A) in the C. thermocellum cellulosome, showing domain architecture, function, localization, proteomics quantitation, structural insights, and recent review context with source citations. This table compiles only claims supported by the provided context IDs.
References (with URLs and dates)
- Zverlov VV, Kellermann J, Schwarz WH. Functional subgenomics of Clostridium thermocellum cellulosomal genes: Identification of the major catalytic components in the extracellular complex and detection of three new enzymes. PROTEOMICS. 2005 Sep;5:3646–3653. https://doi.org/10.1002/pmic.200401199 (zverlov2005functionalsubgenomicsof pages 1-2, zverlov2005functionalsubgenomicsof pages 2-4)
- Gold ND, Martin VJJ. Global View of the Clostridium thermocellum Cellulosome Revealed by Quantitative Proteomic Analysis. J Bacteriol. 2007 Oct;189:6787–6795. https://doi.org/10.1128/JB.00882-07 (gold2007globalviewof pages 2-3)
- Brás JLA. Structure and function relationships in novel cellulosomal enzymes and cohesin–dockerin complexes. 2012. (Structural insights into Cel8A endo-cleft; mini-cellulosome arrangements.) (bras2012structureandfunction pages 56-59)
- Datta R. Enzymatic degradation of cellulose in soil: A review. Heliyon. 2024 Jan;10:e24022. https://doi.org/10.1016/j.heliyon.2024.e24022 (cellulosome architecture; CBM/cohesin–dockerin organization; 2024 perspective) (datta2024enzymaticdegradationof pages 10-12)
References
(zverlov2005functionalsubgenomicsof pages 1-2): Vladimir V. Zverlov, Josef Kellermann, and Wolfgang H. Schwarz. Functional subgenomics of clostridium thermocellum cellulosomal genes: identification of the major catalytic components in the extracellular complex and detection of three new enzymes. PROTEOMICS, 5:3646-3653, Sep 2005. URL: https://doi.org/10.1002/pmic.200401199, doi:10.1002/pmic.200401199. This article has 194 citations and is from a peer-reviewed journal.
(zverlov2005functionalsubgenomicsof pages 2-4): Vladimir V. Zverlov, Josef Kellermann, and Wolfgang H. Schwarz. Functional subgenomics of clostridium thermocellum cellulosomal genes: identification of the major catalytic components in the extracellular complex and detection of three new enzymes. PROTEOMICS, 5:3646-3653, Sep 2005. URL: https://doi.org/10.1002/pmic.200401199, doi:10.1002/pmic.200401199. This article has 194 citations and is from a peer-reviewed journal.
(gold2007globalviewof pages 2-3): 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.
(datta2024enzymaticdegradationof pages 10-12): Rahul Datta. Enzymatic degradation of cellulose in soil: a review. Heliyon, 10:e24022, Jan 2024. URL: https://doi.org/10.1016/j.heliyon.2024.e24022, doi:10.1016/j.heliyon.2024.e24022. This article has 113 citations and is from a peer-reviewed journal.
(bras2012structureandfunction pages 56-59): JLA Brás. Structure and function relationships in novel cellulosomal enzymes and cohesindockerin complexes. Unknown journal, 2012.
---
id: A3DC29
gene_symbol: celA
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: CelA (also known as Cel8A or Endoglucanase A) is a secreted endo-beta-1,4-glucanase
(EC 3.2.1.4) belonging to glycosyl hydrolase family 8 (GH8). It catalyzes the endohydrolysis
of internal (1->4)-beta-D-glucosidic linkages in cellulose, lichenin, and cereal
beta-D-glucans. The enzyme contains a GH8 catalytic domain with an open cleft/groove
architecture characteristic of endo-acting glycosidases, plus a C-terminal type
I dockerin domain (residues 411-477) that mediates incorporation into the cellulosome
complex via cohesin-dockerin interactions with the primary scaffoldin CipA. CelA
is one of the major catalytic components of the C. thermocellum cellulosome, consistently
identified in proteomic surveys of purified cellulosomes grown on Avicel. The enzyme
lacks its own carbohydrate-binding module (CBM) and relies on the CBM of CipA for
targeting to insoluble cellulose substrates. Structural studies at atomic resolution
(0.94 A) have characterized the active site, identifying residues E95 (proton donor)
and D152 (nucleophile) as key catalytic residues.
existing_annotations:
- term:
id: GO:0000272
label: polysaccharide catabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: CelA is an endoglucanase that participates in cellulose degradation.
While cellulose is a polysaccharide, the more specific term GO:0030245 (cellulose
catabolic process) is already annotated and better represents the biological
process. This broader term is acceptable but redundant given the more specific
annotation. The deep research review confirms CelA's role in cellulose breakdown
as part of the cellulosome complex [celA-deep-research-falcon.md].
action: ACCEPT
reason: This annotation is correct but overly broad. CelA specifically degrades
cellulose, which is a type of polysaccharide. The term is inferred from InterPro
domain annotations (IPR002105 Dockerin, IPR016134 Dockerin domain, IPR036439
Dockerin superfamily) which correctly associate the protein with polysaccharide
degradation. Since GO:0030245 (cellulose catabolic process) is also annotated
and is more specific, this broader term is somewhat redundant but not incorrect.
For IEA annotations, broader parent terms are acceptable to retain alongside
more specific ones.
additional_reference_ids: [file:ACET2/celA/celA-deep-research-falcon.md]
- term:
id: GO:0004553
label: hydrolase activity, hydrolyzing O-glycosyl compounds
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: CelA is a glycosyl hydrolase (GH8 family) that hydrolyzes O-glycosyl
compounds, specifically (1->4)-beta-D-glucosidic linkages. This term is correct
but a parent of the more specific GO:0008810 (cellulase activity) which is
also annotated.
action: ACCEPT
reason: This annotation is correct. CelA belongs to GH8 and catalyzes hydrolysis
of beta-glucosidic bonds in cellulose. The annotation is inferred from ARBA
rule ARBA00027782 and InterPro domains IPR002037 (Glyco_hydro_8) and IPR002105
(Dockerin). While GO:0008810 (cellulase activity) is more specific, this parent
term is acceptable for an IEA annotation and provides a useful grouping term.
additional_reference_ids: [file:ACET2/celA/celA-deep-research-falcon.md]
- term:
id: GO:0005975
label: carbohydrate metabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: CelA participates in carbohydrate metabolism through its role in cellulose
degradation. This is a high-level parent term of more specific annotations
already present.
action: ACCEPT
reason: This annotation is correct but very broad. It is inferred from InterPro
records IPR002037 (Glyco_hydro_8), IPR008928 (6-hairpin_glycosidase_sf), and
IPR012341 (6hp_glycosidase-like_sf). While the more specific GO:0030245 (cellulose
catabolic process) better captures CelA's function, this broader term is not
incorrect and acceptable for an IEA annotation derived from domain membership.
additional_reference_ids: [file:ACET2/celA/celA-deep-research-falcon.md]
- term:
id: GO:0008810
label: cellulase activity
evidence_type: IEA
original_reference_id: GO_REF:0000003
review:
summary: CelA (Endoglucanase A) is definitively a cellulase with EC 3.2.1.4
activity. It catalyzes the endohydrolysis of (1->4)-beta-D-glucosidic linkages
in cellulose, lichenin, and cereal beta-D-glucans. This is the core molecular
function of the enzyme and the most specific appropriate MF term.
action: ACCEPT
reason: 'This annotation accurately represents the core molecular function of
CelA. The enzyme is explicitly annotated as EC 3.2.1.4 (endoglucanase/cellulase)
in UniProt, and the GO term definition matches exactly: "Catalysis of the
endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin
and cereal beta-D-glucans." The annotation is derived from the EC number mapping
(GO_REF:0000003). Proteomic studies identify CelA/Cel8A as a major catalytic
component of the cellulosome with endo-beta-1,4-glucanase activity [PMID:16127726,
PMID:17644599]. Structural studies confirm the open cleft architecture characteristic
of endo-acting glycosidases [PMID:8805535].'
additional_reference_ids:
- file:ACET2/celA/celA-deep-research-falcon.md
- PMID:16127726
- PMID:17644599
supported_by:
- reference_id: PMID:16127726
supporting_text: 'Ten of the components were previously known: the structural
protein CipA, the endo-glucanases Cel8A, Cel5G, Cel9N, the cellobiohydrolases
Cbh9A, Cel9K, Cel48S, the xylanases Xyn10C, Xyn10Z, and the chitinase
Chi18A'
- reference_id: PMID:17644599
supporting_text: In total, 41 cellulosomal proteins were detected, including
36 type I dockerin-containing proteins
- term:
id: GO:0016787
label: hydrolase activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: CelA is a hydrolase that cleaves glycosidic bonds. This is a very broad
parent term of the more specific cellulase activity already annotated.
action: ACCEPT
reason: This annotation is correct but extremely broad. CelA is indeed a hydrolase
(EC 3.2.1.4), but the term GO:0008810 (cellulase activity) provides much more
informative functional information. This IEA annotation derived from UniProtKB
keyword KW-0378 (Hydrolase) is acceptable but provides minimal functional
insight beyond what is captured by more specific terms.
additional_reference_ids: [file:ACET2/celA/celA-deep-research-falcon.md]
- term:
id: GO:0016798
label: hydrolase activity, acting on glycosyl bonds
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: CelA hydrolyzes glycosyl bonds, specifically (1->4)-beta-D-glucosidic
linkages. This term is a parent of GO:0004553 (hydrolase activity, hydrolyzing
O-glycosyl compounds) and GO:0008810 (cellulase activity).
action: ACCEPT
reason: This annotation is correct. CelA acts on glycosyl bonds (specifically
beta-1,4 glucosidic bonds in cellulose). The annotation is inferred from UniProtKB
keyword KW-0326 (Glycosidase). While more specific terms are available and
already annotated, this intermediate-level term is acceptable for an IEA.
additional_reference_ids: [file:ACET2/celA/celA-deep-research-falcon.md]
- term:
id: GO:0030245
label: cellulose catabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: CelA is a cellulose-degrading endoglucanase that directly participates
in cellulose catabolism as part of the cellulosome complex. This is the appropriate
biological process term for this enzyme.
action: ACCEPT
reason: This annotation accurately represents CelA's biological role. The enzyme
catalyzes the endohydrolysis of cellulose chains, producing new chain ends
for exoglucanases and contributing directly to cellulose breakdown. The annotation
is derived from UniProtKB keyword KW-0136 (Cellulose degradation). Proteomic
analyses confirm CelA is a major component of the cellulosome, the multi-enzyme
complex responsible for cellulose catabolism in C. thermocellum [PMID:16127726,
PMID:17644599, PMID:38234915].
additional_reference_ids:
- file:ACET2/celA/celA-deep-research-falcon.md
- PMID:16127726
- PMID:38234915
supported_by:
- reference_id: PMID:38234915
supporting_text: the anchoring of various cellulolytic enzymes, i.e., endoglucanases,
cellobiohydrolases, xylanases, to a scaffoldin makes it a complex structure
in which different enzymes work synergistically to attack heterogeneous,
insoluble cellulose substrates
- reference_id: file:ACET2/celA/celA-deep-research-falcon.md
supporting_text: CelA/Cel8A is an endo-beta-1,4-glucanase (EC 3.2.1.4) that
cleaves internal bonds in cellulose chains, producing new chain ends for
exoglucanases
- term:
id: GO:0043263
label: cellulosome
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: CelA contains a type I dockerin domain that mediates its incorporation
into the cellulosome complex. The cellulosome (GO:0043263) is the appropriate
cellular component annotation for this protein.
action: NEW
reason: 'CelA has a well-characterized dockerin domain (residues 411-477) that
binds to type I cohesins on the CipA scaffoldin. Proteomic surveys consistently
identify CelA as a component of purified cellulosomes. This cellular component
annotation should be added, as the protein functions as part of the cellulosome
complex. The InterPro domains IPR002105 (Dockerin_1_rpt), IPR016134 (Dockerin_dom),
and IPR036439 (Dockerin_dom_sf) all indicate cellulosome localization. Note:
This annotation may already exist via IEA but was not present in the provided
GOA file.'
additional_reference_ids:
- file:ACET2/celA/celA-deep-research-falcon.md
- PMID:16127726
- PMID:38234915
supported_by:
- reference_id: PMID:16127726
supporting_text: To identify the predominant catalytic components, cellulosomes
were purified and the components were separated by an adapted two-dimensional
gel electrophoresis technique. The apparent major spots were identified
by MALDI-TOF/TOF
- reference_id: PMID:38234915
supporting_text: 'Cellulosome comprises two major subunits: long flexible
scaffoldin, which forms the center part containing specific binding sites
cohesions, and the enzymes containing a dockerin module that binds to
cohesion'
proposed_replacement_terms:
- id: GO:0043263
label: cellulosome
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:0000120
title: Combined Automated Annotation using Multiple IEA Methods
findings: []
- id: PMID:3980433
title: Sequence of a cellulase gene of the thermophilic bacterium Clostridium
thermocellum
findings:
- statement: Original cloning and sequencing of the celA gene encoding Endoglucanase
A
supporting_text: The nucleotide sequence of the celA gene, encoding the extracellular
endoglucanase A of Clostridium thermocellum, was determined and compared
with the NH2-terminal amino acid sequence of the purified enzyme
- id: PMID:8805535
title: The crystal structure of endoglucanase CelA, a family 8 glycosyl hydrolase
from Clostridium thermocellum
findings:
- statement: Crystal structure at 1.65 A resolution confirms GH8 family fold
with active site cleft
supporting_text: The protein folds into a regular (alpha/alpha)6 barrel formed
by six inner and six outer alpha helices. Cello-oligosaccharides bind to
an acidic cleft containing at least five D-glucosyl-binding subsites
- id: PMID:11884144
title: Atomic (0.94 A) resolution structure of an inverting glycosidase in complex
with substrate
findings:
- statement: High-resolution structure reveals active site and catalytic mechanism
supporting_text: The crystal structure of Clostridium thermocellum endoglucanase
CelA in complex with cellopentaose has been determined at 0.94 A resolution.
The oligosaccharide occupies six D-glucosyl-binding subsites
- id: PMID:16127726
title: Functional subgenomics of Clostridium thermocellum cellulosomal genes
findings:
- statement: CelA/Cel8A identified as one of the major catalytic components
of the cellulosome
supporting_text: 'Ten of the components were previously known: the structural
protein CipA, the endo-glucanases Cel8A, Cel5G, Cel9N, the cellobiohydrolases
Cbh9A, Cel9K, Cel48S, the xylanases Xyn10C, Xyn10Z, and the chitinase Chi18A'
- statement: Seventy-one putative cellulosomal genes detected in C. thermocellum
genome
supporting_text: Seventy-one putative cellulosomal genes were detected. One
third of these ORFs may be involved in cellulose hydrolysis
- id: PMID:17644599
title: Global view of the Clostridium thermocellum cellulosome revealed by quantitative
proteomic analysis
findings:
- statement: Quantitative proteomic analysis of cellulosome composition
supporting_text: In total, 41 cellulosomal proteins were detected, including
36 type I dockerin-containing proteins, which count among them all but three
of the known docking components and 16 new subunits
- id: PMID:38234915
title: Enzymatic degradation of cellulose in soil - A review
findings:
- statement: 2024 review describing cellulosome architecture including CelA
as endoglucanase component
supporting_text: the anchoring of various cellulolytic enzymes, i.e., endoglucanases,
cellobiohydrolases, xylanases, to a scaffoldin makes it a complex structure
in which different enzymes work synergistically to attack heterogeneous,
insoluble cellulose substrates
- id: file:ACET2/celA/celA-deep-research-falcon.md
title: Deep research review of celA gene function
findings:
- statement: Comprehensive literature synthesis on CelA function and cellulosome
localization
supporting_text: CelA/Cel8A is an endo-beta-1,4-glucanase (EC 3.2.1.4) that
cleaves internal bonds in cellulose chains, producing new chain ends for
exoglucanases. Structural evidence shows a groove/open cleft typical of
endo-acting enzymes
core_functions:
- description: Endo-beta-1,4-glucanase activity as part of the cellulosome complex,
catalyzing internal cleavage of cellulose chains to produce new chain ends for
exoglucanases.
molecular_function:
id: GO:0008810
label: cellulase activity
directly_involved_in:
- id: GO:0030245
label: cellulose catabolic process
locations:
- id: GO:0043263
label: cellulosome
supported_by:
- reference_id: PMID:16127726
supporting_text: 'Ten of the components were previously known: the structural
protein CipA, the endo-glucanases Cel8A, Cel5G, Cel9N'
- reference_id: PMID:17644599
supporting_text: In total, 41 cellulosomal proteins were detected, including
36 type I dockerin-containing proteins
suggested_questions:
- question: What is the precise substrate specificity of CelA compared to other
GH8 endoglucanases in the cellulosome? Does it show any preference for specific
regions of crystalline vs amorphous cellulose?
experts: []
- question: How does CelA synergize with exoglucanases (like CelS/Cel48A) and other
endoglucanases in the cellulosome to achieve efficient cellulose degradation?
experts: []
suggested_experiments:
- hypothesis: CelA shows optimal activity when incorporated into the cellulosome
complex compared to free enzyme, due to proximity effects with other cellulases.
description: Compare the kinetic parameters (kcat, Km) of CelA in free form versus
when bound to mini-cellulosomes containing different combinations of other cellulases.
Use defined cellulose substrates (Avicel, filter paper, CMC, phosphoric acid
swollen cellulose) to assess potential synergistic effects.
experiment_type: enzyme kinetics
tags: [cellulosome]