LicB (also known as Lam1) is a thermostable beta-glucanase (lichenase, EC 3.2.1.73) from Acetivibrio thermocellus (formerly Clostridium thermocellum). It is a GH16 family glycoside hydrolase that catalyzes the endohydrolysis of (1->4)-beta-D-glucosidic linkages in mixed-linkage beta-D-glucans containing both (1->3) and (1->4) bonds, such as lichenan and barley beta-glucan. The enzyme contains a C-terminal type-I dockerin domain that enables its incorporation into the cellulosome, the large extracellular enzyme complex characteristic of this bacterium that efficiently degrades plant cell wall polysaccharides.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0000272
polysaccharide catabolic process
|
IEA
GO_REF:0000002 |
MODIFY |
Summary: This IEA annotation is derived from InterPro domain matches (IPR002105, IPR016134, IPR036439 - dockerin domains). While LicB does participate in polysaccharide catabolism, this term is too general. The enzyme specifically degrades mixed-linkage beta-glucans. A more specific term like 'beta-glucan catabolic process' (GO:0051275) would be more accurate.
Reason: The term 'polysaccharide catabolic process' is overly broad. LicB is a lichenase that specifically hydrolyzes beta-glucans containing (1->3) and (1->4) linkages. UniProt confirms the catalytic activity with EC 3.2.1.73. A more specific biological process term should be used.
Proposed replacements:
beta-glucan catabolic process
Supporting Evidence:
UniProtKB:Q84C00
Hydrolysis of (1->4)-beta-D-glucosidic linkages in beta-D- glucans containing (1->3)- and (1->4)-bonds.
file:ACET2/Q84C00/Q84C00-deep-research-falcon.md
LicB is a GH16 family lichenase that degrades beta-glucans
|
|
GO:0004553
hydrolase activity, hydrolyzing O-glycosyl compounds
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: This annotation is correct but represents a high-level parent term. LicB does indeed have O-glycosyl hydrolase activity, but the specific term 'licheninase activity' (GO:0042972) already captures this more precisely. This annotation can be retained as it is not incorrect, but it provides less information than the more specific term.
Reason: While this is a general parent term, it is not incorrect for LicB. The enzyme hydrolyzes O-glycosyl bonds in beta-glucans. Since the more specific 'licheninase activity' (GO:0042972) is also annotated, this broader term provides hierarchical context and is acceptable to retain.
Supporting Evidence:
UniProtKB:Q84C00
Belongs to the glycosyl hydrolase 16 family.
|
|
GO:0005975
carbohydrate metabolic process
|
IEA
GO_REF:0000002 |
MODIFY |
Summary: This is a very high-level biological process term. While technically correct (lichenase participates in carbohydrate metabolism), this term is too general to be informative. It should be replaced with a more specific term.
Reason: 'Carbohydrate metabolic process' is the grandparent term for nearly all sugar-related processes. For a specific enzyme like lichenase, a more informative term such as 'beta-glucan catabolic process' (GO:0051275) should be used to accurately reflect the enzyme's biological role.
Proposed replacements:
beta-glucan catabolic process
Supporting Evidence:
UniProtKB:Q84C00
Hydrolysis of (1->4)-beta-D-glucosidic linkages in beta-D- glucans containing (1->3)- and (1->4)-bonds.
|
|
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 LicB is indeed a hydrolase, this is the root molecular function term for all hydrolases and is too general to be informative when more specific terms are available.
Reason: The term 'hydrolase activity' is the most general hydrolase term in GO. Since LicB already has the specific annotation 'licheninase activity' (GO:0042972), retaining this very general term adds no informational value and clutters the annotation set.
Supporting Evidence:
UniProtKB:Q84C00
Glycosidase; Hydrolase; Signal.
|
|
GO:0016798
hydrolase activity, acting on glycosyl bonds
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: This annotation comes from UniProtKB keyword mapping (KW-0326 Glycosidase). It is a parent term of 'hydrolase activity, hydrolyzing O-glycosyl compounds' (GO:0004553). While correct, it is redundant given the presence of more specific glycosidase terms.
Reason: This term correctly captures the glycosidase activity of LicB. Although it is a mid-level term in the hierarchy (parent of GO:0004553), it is informative enough to retain alongside the specific 'licheninase activity' term. It provides appropriate hierarchical context.
Supporting Evidence:
UniProtKB:Q84C00
Belongs to the glycosyl hydrolase 16 family.
|
|
GO:0042972
licheninase activity
|
IEA
GO_REF:0000003 |
ACCEPT |
Summary: This is the most specific and accurate molecular function annotation for LicB. Licheninase activity (EC 3.2.1.73) catalyzes the hydrolysis of (1->4)-beta-D- glucosidic linkages in beta-D-glucans containing (1->3) and (1->4) bonds. This precisely matches the documented function of LicB.
Reason: This annotation is derived from EC number mapping (EC:3.2.1.73) and accurately represents the core molecular function of LicB. UniProt explicitly assigns EC 3.2.1.73 to this enzyme, and the catalytic activity described matches the GO term definition exactly. This is the primary functional annotation for this enzyme.
Supporting Evidence:
UniProtKB:Q84C00
RecName: Full=Beta-glucanase;
|
|
GO:1990311
type-I cohesin domain binding
|
ISS
UniProtKB:Q84C00 |
NEW |
Summary: LicB contains a type-I dockerin domain (residues 267-334) that mediates binding to type-I cohesin domains on the CipA scaffoldin protein of the cellulosome. This domain architecture is characteristic of cellulosomal enzymes in A. thermocellus.
Reason: The UniProt entry clearly documents a dockerin domain (PROSITE pattern PS51766). The dockerin domain binds to cohesin domains on the scaffoldin protein, enabling incorporation of the enzyme into the cellulosome. This is a core function of the protein enabling its biological role in extracellular polysaccharide degradation.
Supporting Evidence:
UniProtKB:Q84C00
InterPro; IPR002105; Dockerin_1_rpt.
|
|
GO:0043263
cellulosome
|
ISS
UniProtKB:Q84C00 |
NEW |
Summary: LicB is a component of the cellulosome based on its dockerin domain, which mediates attachment to the scaffoldin. The cellulosome is the characteristic extracellular enzyme complex of A. thermocellus.
Reason: The presence of a type-I dockerin domain (IPR002105, PS51766) strongly indicates that LicB is a cellulosomal enzyme. The dockerin domain is the hallmark of cellulosomal enzymes in Clostridia, enabling their incorporation into the multi-enzyme complex via binding to cohesin domains on the scaffoldin.
Supporting Evidence:
UniProtKB:Q84C00
PROSITE; PS00448; CLOS_CELLULOSOME_RPT; 2.
|
Q: What is the substrate specificity of LicB compared to other GH16 enzymes in A. thermocellus? Does it preferentially cleave lichenan vs barley beta-glucan?
Q: Is LicB constitutively expressed or is its expression regulated by carbon source availability?
Experiment: Kinetic characterization of recombinant LicB with different beta-glucan substrates (lichenan, barley beta-glucan, laminarin) to determine substrate specificity and kinetic parameters.
Hypothesis: Would provide quantitative data to better annotate substrate specificity.
Experiment: Pulldown or co-IP experiments to confirm cellulosome incorporation and identify specific cohesin binding partners.
Hypothesis: Would provide direct experimental evidence for cellulosome localization annotation.
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template_file: templates/gene_research_go_focused.md
template_variables:
organism: ACET2
gene_id: Q84C00
gene_symbol: licB
uniprot_accession: Q84C00
protein_description: 'RecName: Full=Beta-glucanase; EC=3.2.1.73; AltName: Full=1,3-1,4-beta-D-glucan
4-glucanohydrolase; AltName: Full=Endo-beta-1,3-1,4 glucanase; AltName: Full=Laminarinase;
AltName: Full=Lichenase; Flags: Precursor;'
gene_info: Name=licB; Synonyms=lam1;
organism_full: Acetivibrio thermocellus (Hungateiclostridium thermocellum) (Clostridium
thermocellum).
protein_family: Belongs to the glycosyl hydrolase 16 family. .
protein_domains: Beta-glucanase/XTH. (IPR044791); Beta_glucanase. (IPR008264); ConA-like_dom_sf.
(IPR013320); Dockerin_1_rpt. (IPR002105); Dockerin_dom. (IPR016134)
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citation_count: 18
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 'licB' 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 licB (gene ID: Q84C00, UniProt: Q84C00) 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 'licB' 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 licB (gene ID: Q84C00, UniProt: Q84C00) 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
- Verified target identity and nomenclature, given symbol ambiguity. LicB in Clostridium thermocellum (synonyms: Hungateiclostridium thermocellum; Acetivibrio thermocellus) corresponds to a GH16 lichenase (EC 3.2.1.73) with a dockerin module and is incorporated into the cellulosome; proteomic datasets detect LicB specifically in isolated C. thermocellum cellulosomes (URLs and dates provided below). Focused the review on function, substrate specificity, domain architecture, localization, pathway context, and applications. (gold2007proteomicanalysisof pages 77-79, gold2007globalviewof pages 6-8, schwarz2004extracellularglycosylhydrolases pages 22-26)
Gene/protein verification and identity
- Symbol disambiguation: “licB” is used across bacteria; here, licB encodes a GH16 lichenase in C. thermocellum (Acetivibrio/Hungateiclostridium thermocellum). Quantitative proteomics of C. thermocellum cellulosomes lists “LicB lichenase (GH16)” among identified enzymes, providing organism- and gene-level confirmation. The study mapped proteins in affinity-isolated cellulosomes by LC–MS/MS, with stringent filters for secreted proteins, and reports LicB detection metrics (emPAI), establishing the correct protein identity and context. Journal of Bacteriology, 2007-10 (URL: https://doi.org/10.1128/jb.00882-07). (gold2007globalviewof pages 6-8, gold2007proteomicanalysisof pages 50-55, gold2007proteomicanalysisof pages 77-79)
1) Key concepts and definitions
- Enzyme class and reaction: LicB is a lichenase (EC 3.2.1.73), an endo-β-1,3/1,4-glucanase that cleaves β-1,4 glycosidic bonds adjacent to β-1,3 linkages in mixed-linkage glucans (e.g., lichenan and cereal β-glucans), producing predominantly trisaccharides and tetrasaccharides from these substrates; it is not a cellulase acting on crystalline cellulose. Reviews of clostridial extracellular glycosyl hydrolases and cellulosome composition categorize GH16 lichenases as hemicellulases targeting mixed-linkage β-glucans within plant cell walls rather than cellulose microfibrils. Advances in Applied Microbiology, 2004-01 (URL: https://doi.org/10.1016/S0065-2164(04)56007-0). (schwarz2004extracellularglycosylhydrolases pages 22-26)
- Cellulosome architecture and localization: In C. thermocellum, cellulosomes are extracellular, multienzyme complexes organized by a noncatalytic scaffoldin (CipA) bearing a cellulose-binding module and multiple type I cohesins that recruit catalytic enzymes via type I dockerins; scaffoldin attachment to the cell surface involves type II dockerin/cohesin interactions on anchoring proteins with SLH motifs. This architecture positions enzymes at the cell–substrate interface and can also yield cell-free extracellular complexes later in growth. Microbiology and Molecular Biology Reviews, 2005-03 (URL: https://doi.org/10.1128/MMBR.69.1.124-154.2005); Journal of Structural Biology, 1998-12 (URL: https://doi.org/10.1006/jsbi.1998.4065). (demain2005cellulaseclostridiaand pages 6-7, bayer1998cellulosomesstructureandultrastructure. pages 6-7, munir2014cellulosehydrolysisand pages 37-42)
2) Recent developments and latest research (2023–2025 context)
- Contemporary perspectives on cellulosome structure/function and cohesin–dockerin specificity emphasize modular assembly, dynamic composition, and engineering opportunities (designer cellulosomes), situating GH16 hemicellulases like LicB as accessory enzymes that increase deconstruction efficiency by removing matrix polysaccharides. Frontiers in Microbiology, 2025-09 (URL: https://doi.org/10.3389/fmicb.2025.1638551). Although beyond 2024, this review synthesizes recent advances pertinent to LicB’s role within the ensemble. (lindic2025structuralandfunctional pages 19-20, lindic2025structuralandfunctional pages 19-19)
- Proteome-centric views continue to validate dockerin-bearing hemicellulases in cellulosomes and to highlight condition-dependent incorporation (e.g., differential detection of specific enzymes on Avicel vs other carbon sources), consistent with adaptive inclusion of GH16 lichenase LicB. Journal of Bacteriology, 2007-10 (URL: https://doi.org/10.1128/jb.00882-07). Methods details for confident identification of secreted, cellulosome-associated enzymes are described (LC–MS/MS after cellulose-affinity purification; signals for secretion required), which remain methodological standards. (gold2007globalviewof pages 6-8, gold2007proteomicanalysisof pages 50-55)
3) Current applications and implementations
- Biomass deconstruction and biofuels: Cellulosomes, including hemicellulases such as GH16 lichenases, enhance plant cell wall degradation by synergistically removing noncellulosic barriers to cellulose; this supports consolidated bioprocessing strategies for lignocellulosic bioethanol in thermophilic clostridia. Foundational and expert reviews on clostridia and cellulosomes frame these applications and the extracellular deployment of enzyme consortia. Microbiology and Molecular Biology Reviews, 2005-03 (URL: https://doi.org/10.1128/MMBR.69.1.124-154.2005). (demain2005cellulaseclostridiaand pages 6-7)
- Designer/synthetic cellulosomes: Recent expert reviews summarize progress in reconstituting/engineering cellulosomes to optimize enzyme sets (including hemicellulases) for various substrates, reinforcing the practical value of incorporating GH16 activities to access mixed-linkage glucans in grasses and cereals. Frontiers in Microbiology, 2025-09 (URL: https://doi.org/10.3389/fmicb.2025.1638551). (lindic2025structuralandfunctional pages 19-20, lindic2025structuralandfunctional pages 19-19)
4) Expert opinions and analysis from authoritative sources
- Extracellular, modular design is central to efficiency. Canonical reviews emphasize that a scaffoldin with a cellulose-binding module recruits dockerin-bearing enzymes to the substrate surface, enabling proximity and synergy; hemicellulases such as GH16 lichenases contribute by peeling away matrix glucans that otherwise impede cellulase access. Journal of Structural Biology, 1998-12 (URL: https://doi.org/10.1006/jsbi.1998.4065); Microbiology and Molecular Biology Reviews, 2005-03 (URL: https://doi.org/10.1128/MMBR.69.1.124-154.2005). (bayer1998cellulosomesstructureandultrastructure. pages 6-7, demain2005cellulaseclostridiaand pages 6-7)
- Adaptive composition and detection: Quantitative proteomics revealed condition-specific incorporation of cellulosomal enzymes and detected LicB in Avicel-derived complexes, supporting the view that GH16 lichenases are selectively deployed to facilitate degradation of plant materials rich in mixed-linkage glucans. Journal of Bacteriology, 2007-10 (URL: https://doi.org/10.1128/jb.00882-07). (gold2007globalviewof pages 6-8)
5) Relevant statistics and data from recent and primary studies
- Proteomic identification of LicB in isolated cellulosomes: LicB (annotated GH16 lichenase) appears in cellulosome proteomes with quantitative metrics (e.g., emPAI ~0.30 in a representative dataset) following stringent identification criteria (≥2 unique peptides; signal peptide; cellulose-affinity isolation), supporting its bona fide inclusion in the complex. Experimental workflow and identification thresholds are detailed and widely adopted. Journal of Bacteriology, 2007-10 (URL: https://doi.org/10.1128/jb.00882-07); additional proteomic methods description provided in a complementary analysis. (gold2007proteomicanalysisof pages 77-79, gold2007proteomicanalysisof pages 50-55, gold2007globalviewof pages 6-8)
- Domain/module annotation: Reviews of clostridial extracellular glycosyl hydrolases explicitly classify LicB as GH16 with a dockerin type I (GH16–Doc1), consistent with cellulosomal catalytic components recruited to the primary scaffoldin (CipA); this implies an N-terminal signal peptide for secretion and C-terminal dockerin for complex assembly. Advances in Applied Microbiology, 2004-01 (URL: https://doi.org/10.1016/S0065-2164(04)56007-0). (schwarz2004extracellularglycosylhydrolases pages 22-26)
Functional annotation for licB (Q84C00) in C. thermocellum
- Primary function and reaction: LicB encodes a GH16 lichenase that hydrolyzes β-1,4 linkages adjacent to β-1,3 linkages within mixed-linkage β-glucans (e.g., lichenan, cereal β-glucan), consistent with EC 3.2.1.73. It contributes to hemicellulose/mixed-linkage glucan deconstruction rather than crystalline cellulose hydrolysis. Advances in Applied Microbiology, 2004-01 (URL: https://doi.org/10.1016/S0065-2164(04)56007-0). (schwarz2004extracellularglycosylhydrolases pages 22-26)
- Substrate specificity: Mixed-linkage β-glucans in plant cell walls (lichenan, barley/oat β-glucan) are canonical substrates for GH16 lichenases; these are matrix polysaccharides distinct from cellulose. LicB is consistently grouped with GH16 lichenases in C. thermocellum cellulosomes, indicating this specificity in vivo. Advances in Applied Microbiology, 2004-01 (URL: https://doi.org/10.1016/S0065-2164(04)56007-0); Journal of Bacteriology, 2007-10 (URL: https://doi.org/10.1128/jb.00882-07). (schwarz2004extracellularglycosylhydrolases pages 22-26, gold2007globalviewof pages 6-8)
- Domain architecture and localization: Evidence indicates a secreted modular enzyme architecture: N-terminal signal peptide for secretion; GH16 catalytic domain; C-terminal type I dockerin (Doc1) that tethers the enzyme to CipA type I cohesins within the extracellular cellulosome attached to cellulose and, via anchor scaffoldins, to the cell surface. Advances in Applied Microbiology, 2004-01 (URL: https://doi.org/10.1016/S0065-2164(04)56007-0); Journal of Structural Biology, 1998-12 (URL: https://doi.org/10.1006/jsbi.1998.4065); Microbiology and Molecular Biology Reviews, 2005-03 (URL: https://doi.org/10.1128/MMBR.69.1.124-154.2005). (schwarz2004extracellularglycosylhydrolases pages 22-26, bayer1998cellulosomesstructureandultrastructure. pages 6-7, demain2005cellulaseclostridiaand pages 6-7)
- Proteomic and gene-level evidence supporting cellulosome incorporation: LicB is directly detected in affinity-purified cellulosomes of C. thermocellum by LC–MS/MS, with quantitative values reported and with methodology that required secretion signals; a related analysis lists LicB (GH16 lichenase) explicitly in the cellulosome protein catalog. Journal of Bacteriology, 2007-10 (URL: https://doi.org/10.1128/jb.00882-07); complementary proteomic methods resource. (gold2007globalviewof pages 6-8, gold2007proteomicanalysisof pages 77-79, gold2007proteomicanalysisof pages 50-55)
Pathway and systems context
- Role within plant cell wall deconstruction: GH16 lichenases in the cellulosome act as accessory hemicellulases to remove mixed-linkage β-glucans that encase or cross-link cellulose microfibrils, thereby increasing cellulase access and improving overall saccharification. Classic reviews on cellulosome structure and extracellular localization support this mechanistic role for noncellulase components within the multienzyme assembly. Microbiology and Molecular Biology Reviews, 2005-03 (URL: https://doi.org/10.1128/MMBR.69.1.124-154.2005); Journal of Structural Biology, 1998-12 (URL: https://doi.org/10.1006/jsbi.1998.4065). (demain2005cellulaseclostridiaand pages 6-7, bayer1998cellulosomesstructureandultrastructure. pages 6-7)
Ambiguity note
- The symbol licB is used in multiple bacteria (sometimes for lichenases or unrelated functions), but proteomic identification in C. thermocellum cellulosomes and authoritative reviews of clostridial extracellular GHs confirm that, in this organism, licB encodes a GH16 lichenase with a dockerin module integrated into the cellulosome. Journal of Bacteriology, 2007-10 (URL: https://doi.org/10.1128/jb.00882-07); Advances in Applied Microbiology, 2004-01 (URL: https://doi.org/10.1016/S0065-2164(04)56007-0). (gold2007globalviewof pages 6-8, schwarz2004extracellularglycosylhydrolases pages 22-26)
Limitations and open needs
- Although the proteomic and review literature strongly supports LicB’s function and localization, enzyme kinetics and precise pH/temperature optima for LicB specifically were not captured in the accessible excerpts; targeted biochemical characterization and structural data for the LicB catalytic module (GH16) would further refine the annotation. The cellulosome-focused reviews from 2023–2025 strengthen the systems context but provide limited LicB-specific quantitative biochemistry. Additional recent primary studies focused directly on LicB would be valuable for detailed kinetic parameters. (lindic2025structuralandfunctional pages 19-20, gold2007globalviewof pages 6-8)
References
(gold2007proteomicanalysisof pages 77-79): N Gold. Proteomic analysis of the clostridium thermocellum cellulosome. Unknown journal, 2007.
(gold2007globalviewof pages 6-8): 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.
(schwarz2004extracellularglycosylhydrolases pages 22-26): Wolfgang H. Schwarz, Vladimir V. Zverlov, and Hubert Bahl. Extracellular glycosyl hydrolases from clostridia. Advances in applied microbiology, 56:215-61, Jan 2004. URL: https://doi.org/10.1016/s0065-2164(04)56007-0, doi:10.1016/s0065-2164(04)56007-0. This article has 65 citations.
(gold2007proteomicanalysisof pages 50-55): N Gold. Proteomic analysis of the clostridium thermocellum cellulosome. Unknown journal, 2007.
(demain2005cellulaseclostridiaand pages 6-7): Arnold L. Demain, Michael Newcomb, and J. H. David Wu. Cellulase, clostridia, and ethanol. Microbiology and Molecular Biology Reviews, 69:124-154, Mar 2005. URL: https://doi.org/10.1128/mmbr.69.1.124-154.2005, doi:10.1128/mmbr.69.1.124-154.2005. This article has 1268 citations and is from a domain leading peer-reviewed journal.
(bayer1998cellulosomesstructureandultrastructure. pages 6-7): Edward A. Bayer, Linda J.W. Shimon, Yuval Shoham, and Raphael Lamed. Cellulosomes-structure and ultrastructure. Journal of structural biology, 124 2-3:221-34, Dec 1998. URL: https://doi.org/10.1006/jsbi.1998.4065, doi:10.1006/jsbi.1998.4065. This article has 474 citations and is from a peer-reviewed journal.
(munir2014cellulosehydrolysisand pages 37-42): R Munir. Cellulose hydrolysis and metabolism in the mesophilic, cellulolytic bacterium, clostridium termitidis ct1112. Unknown journal, 2014.
(lindic2025structuralandfunctional pages 19-20): Nataša Lindič and Maša Vodovnik. Structural and functional insights into cellulosomes: masters of plant cell wall degradation. Frontiers in Microbiology, Sep 2025. URL: https://doi.org/10.3389/fmicb.2025.1638551, doi:10.3389/fmicb.2025.1638551. This article has 1 citations and is from a poor quality or predatory journal.
(lindic2025structuralandfunctional pages 19-19): Nataša Lindič and Maša Vodovnik. Structural and functional insights into cellulosomes: masters of plant cell wall degradation. Frontiers in Microbiology, Sep 2025. URL: https://doi.org/10.3389/fmicb.2025.1638551, doi:10.3389/fmicb.2025.1638551. This article has 1 citations and is from a poor quality or predatory journal.
id: Q84C00
gene_symbol: licB
aliases:
- LicB
- Laminarinase
- Beta-1,3-1,4-glucanase
product_type: PROTEIN
status: DRAFT
taxon:
id: NCBITaxon:1515
label: Acetivibrio thermocellus
description: >-
LicB (also known as Lam1) is a thermostable beta-glucanase (lichenase, EC 3.2.1.73)
from Acetivibrio thermocellus (formerly Clostridium thermocellum). It is a GH16
family glycoside hydrolase that catalyzes the endohydrolysis of (1->4)-beta-D-glucosidic
linkages in mixed-linkage beta-D-glucans containing both (1->3) and (1->4) bonds,
such as lichenan and barley beta-glucan. The enzyme contains a C-terminal type-I
dockerin domain that enables its incorporation into the cellulosome, the large
extracellular enzyme complex characteristic of this bacterium that efficiently
degrades plant cell wall polysaccharides.
existing_annotations:
- term:
id: GO:0000272
label: polysaccharide catabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
This IEA annotation is derived from InterPro domain matches (IPR002105,
IPR016134, IPR036439 - dockerin domains). While LicB does participate in
polysaccharide catabolism, this term is too general. The enzyme specifically
degrades mixed-linkage beta-glucans. A more specific term like
'beta-glucan catabolic process' (GO:0051275) would be more accurate.
action: MODIFY
reason: >-
The term 'polysaccharide catabolic process' is overly broad. LicB is a
lichenase that specifically hydrolyzes beta-glucans containing (1->3) and
(1->4) linkages. UniProt confirms the catalytic activity with EC 3.2.1.73.
A more specific biological process term should be used.
proposed_replacement_terms:
- id: GO:0051275
label: beta-glucan catabolic process
supported_by:
- reference_id: UniProtKB:Q84C00
supporting_text: >-
Hydrolysis of (1->4)-beta-D-glucosidic linkages in beta-D-
glucans containing (1->3)- and (1->4)-bonds.
- reference_id: file:ACET2/Q84C00/Q84C00-deep-research-falcon.md
supporting_text: "LicB is a GH16 family lichenase that degrades beta-glucans"
- term:
id: GO:0004553
label: hydrolase activity, hydrolyzing O-glycosyl compounds
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
This annotation is correct but represents a high-level parent term. LicB does
indeed have O-glycosyl hydrolase activity, but the specific term 'licheninase
activity' (GO:0042972) already captures this more precisely. This annotation
can be retained as it is not incorrect, but it provides less information than
the more specific term.
action: ACCEPT
reason: >-
While this is a general parent term, it is not incorrect for LicB. The enzyme
hydrolyzes O-glycosyl bonds in beta-glucans. Since the more specific
'licheninase activity' (GO:0042972) is also annotated, this broader term
provides hierarchical context and is acceptable to retain.
supported_by:
- reference_id: UniProtKB:Q84C00
supporting_text: >-
Belongs to the glycosyl hydrolase 16 family.
- term:
id: GO:0005975
label: carbohydrate metabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
This is a very high-level biological process term. While technically correct
(lichenase participates in carbohydrate metabolism), this term is too general
to be informative. It should be replaced with a more specific term.
action: MODIFY
reason: >-
'Carbohydrate metabolic process' is the grandparent term for nearly all
sugar-related processes. For a specific enzyme like lichenase, a more
informative term such as 'beta-glucan catabolic process' (GO:0051275)
should be used to accurately reflect the enzyme's biological role.
proposed_replacement_terms:
- id: GO:0051275
label: beta-glucan catabolic process
supported_by:
- reference_id: UniProtKB:Q84C00
supporting_text: >-
Hydrolysis of (1->4)-beta-D-glucosidic linkages in beta-D-
glucans containing (1->3)- and (1->4)-bonds.
- term:
id: GO:0016787
label: hydrolase activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
This annotation is derived from UniProtKB keyword mapping (KW-0378 Hydrolase).
While LicB is indeed a hydrolase, this is the root molecular function term for
all hydrolases and is too general to be informative when more specific terms
are available.
action: MARK_AS_OVER_ANNOTATED
reason: >-
The term 'hydrolase activity' is the most general hydrolase term in GO.
Since LicB already has the specific annotation 'licheninase activity'
(GO:0042972), retaining this very general term adds no informational value
and clutters the annotation set.
supported_by:
- reference_id: UniProtKB:Q84C00
supporting_text: >-
Glycosidase; Hydrolase; Signal.
- term:
id: GO:0016798
label: hydrolase activity, acting on glycosyl bonds
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
This annotation comes from UniProtKB keyword mapping (KW-0326 Glycosidase).
It is a parent term of 'hydrolase activity, hydrolyzing O-glycosyl compounds'
(GO:0004553). While correct, it is redundant given the presence of more
specific glycosidase terms.
action: ACCEPT
reason: >-
This term correctly captures the glycosidase activity of LicB. Although it
is a mid-level term in the hierarchy (parent of GO:0004553), it is informative
enough to retain alongside the specific 'licheninase activity' term. It
provides appropriate hierarchical context.
supported_by:
- reference_id: UniProtKB:Q84C00
supporting_text: >-
Belongs to the glycosyl hydrolase 16 family.
- term:
id: GO:0042972
label: licheninase activity
evidence_type: IEA
original_reference_id: GO_REF:0000003
review:
summary: >-
This is the most specific and accurate molecular function annotation for LicB.
Licheninase activity (EC 3.2.1.73) catalyzes the hydrolysis of (1->4)-beta-D-
glucosidic linkages in beta-D-glucans containing (1->3) and (1->4) bonds. This
precisely matches the documented function of LicB.
action: ACCEPT
reason: >-
This annotation is derived from EC number mapping (EC:3.2.1.73) and accurately
represents the core molecular function of LicB. UniProt explicitly assigns
EC 3.2.1.73 to this enzyme, and the catalytic activity described matches
the GO term definition exactly. This is the primary functional annotation
for this enzyme.
supported_by:
- reference_id: UniProtKB:Q84C00
supporting_text: >-
RecName: Full=Beta-glucanase;
- term:
id: GO:1990311
label: type-I cohesin domain binding
evidence_type: ISS
original_reference_id: UniProtKB:Q84C00
review:
summary: >-
LicB contains a type-I dockerin domain (residues 267-334) that mediates
binding to type-I cohesin domains on the CipA scaffoldin protein of the
cellulosome. This domain architecture is characteristic of cellulosomal
enzymes in A. thermocellus.
action: NEW
reason: >-
The UniProt entry clearly documents a dockerin domain (PROSITE pattern
PS51766). The dockerin domain binds to cohesin domains on the scaffoldin
protein, enabling incorporation of the enzyme into the cellulosome. This
is a core function of the protein enabling its biological role in
extracellular polysaccharide degradation.
supported_by:
- reference_id: UniProtKB:Q84C00
supporting_text: >-
InterPro; IPR002105; Dockerin_1_rpt.
- term:
id: GO:0043263
label: cellulosome
evidence_type: ISS
original_reference_id: UniProtKB:Q84C00
review:
summary: >-
LicB is a component of the cellulosome based on its dockerin domain, which
mediates attachment to the scaffoldin. The cellulosome is the characteristic
extracellular enzyme complex of A. thermocellus.
action: NEW
reason: >-
The presence of a type-I dockerin domain (IPR002105, PS51766) strongly
indicates that LicB is a cellulosomal enzyme. The dockerin domain is the
hallmark of cellulosomal enzymes in Clostridia, enabling their incorporation
into the multi-enzyme complex via binding to cohesin domains on the scaffoldin.
supported_by:
- reference_id: UniProtKB:Q84C00
supporting_text: >-
PROSITE; PS00448; CLOS_CELLULOSOME_RPT; 2.
references:
- id: UniProtKB:Q84C00
title: UniProt entry for LicB (Beta-glucanase) from Acetivibrio thermocellus
findings:
- statement: EC 3.2.1.73 (licheninase) assignment confirmed
supporting_text: >-
RecName: Full=Beta-glucanase;
- statement: GH16 domain identified (residues 28-248)
supporting_text: >-
Pfam; PF00722; Glyco_hydro_16; 1.
- statement: Dockerin domain identified (residues 267-334)
supporting_text: >-
Pfam; PF00404; Dockerin_1; 1.
- statement: Active site residues identified at positions 136 and 140
supporting_text: >-
/evidence="ECO:0000255|PROSITE-ProRule:PRU10064"
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO terms
findings:
- statement: Source of IEA annotations based on domain matches
- id: GO_REF:0000003
title: Gene Ontology annotation based on Enzyme Commission mapping
findings:
- statement: Source of licheninase activity annotation from EC 3.2.1.73 mapping
- id: GO_REF:0000043
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
findings:
- statement: Source of general hydrolase annotations from UniProt keywords
- id: PMID:1755832
title: Nucleotide sequence of the Clostridium thermocellum laminarinase gene
findings:
- statement: Original cloning and sequencing of the licB gene
supporting_text: "The sequence presented (1022 bp) shows the Clostridium thermocellum laminarinase gene (lam1) and its flanking regions"
- statement: Gene was originally named laminarinase (lam1)
supporting_text: "The gene lam1 comprises an open reading frame of 726 nt, encoding a 242-aa protein with predicted Mr 27661"
core_functions:
- molecular_function:
id: GO:0042972
label: licheninase activity
description: >-
LicB is definitively a licheninase (EC 3.2.1.73) based on UniProt annotation
and enzyme classification. This is its primary catalytic function.
directly_involved_in:
- id: GO:0051275
label: beta-glucan catabolic process
locations:
- id: GO:0043263
label: cellulosome
proposed_new_terms: []
suggested_questions:
- question: >-
What is the substrate specificity of LicB compared to other GH16 enzymes
in A. thermocellus? Does it preferentially cleave lichenan vs barley beta-glucan?
- question: >-
Is LicB constitutively expressed or is its expression regulated by carbon
source availability?
suggested_experiments:
- description: >-
Kinetic characterization of recombinant LicB with different beta-glucan
substrates (lichenan, barley beta-glucan, laminarin) to determine substrate
specificity and kinetic parameters.
hypothesis: >-
Would provide quantitative data to better annotate substrate specificity.
- description: >-
Pulldown or co-IP experiments to confirm cellulosome incorporation and
identify specific cohesin binding partners.
hypothesis: >-
Would provide direct experimental evidence for cellulosome localization
annotation.