CelK (also known as Cel9K, locus Cthe_0412) is a major cellulosomal cellulase belonging to glycoside hydrolase family 9 (GH9) in Acetivibrio thermocellus (formerly Clostridium thermocellum). It functions as a cellulose 1,4-beta-cellobiosidase (EC 3.2.1.91) that hydrolyzes beta-1,4-glucosidic linkages in cellulose, releasing cellobiose and cellotriose from the non-reducing ends of cellulose chains. The enzyme has a modular architecture consisting of a CBM4 carbohydrate-binding module, an Ig-like domain, the GH9 catalytic domain, and a C-terminal type I dockerin domain that mediates integration into the cellulosome complex. CelK works synergistically with Cel48S (the major GH48 cellobiohydrolase) in the cellulosome to efficiently degrade crystalline cellulose.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0000272
polysaccharide catabolic process
|
IEA
GO_REF:0000120 |
MODIFY |
Summary: CelK is a cellulase that degrades cellulose, which is a polysaccharide. The annotation to polysaccharide catabolic process is correct but overly broad. CelK specifically catalyzes the breakdown of cellulose (a beta-1,4-glucan), not polysaccharides in general.
Reason: While cellulose is a polysaccharide and CelK does participate in polysaccharide catabolism, this term is too general. The more specific term GO:0030245 (cellulose catabolic process) already exists in the annotation set and accurately captures the biological process. This broader term provides less informative annotation.
Proposed replacements:
cellulose catabolic process
Supporting Evidence:
PMID:29075324
CBHs (exo-acting from the sugar ends) released specifically cellobiose as the only product over time (Cel48S, Cel9K, and Cbh9A)
|
|
GO:0004553
hydrolase activity, hydrolyzing O-glycosyl compounds
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: CelK is a GH9 family glycoside hydrolase that hydrolyzes beta-1,4-glucosidic bonds in cellulose. This annotation is correct but too general - the enzyme has specific cellobiohydrolase activity (EC 3.2.1.91) rather than generic glycosyl hydrolase activity.
Reason: While GO:0016162 (cellulose 1,4-beta-cellobiosidase activity) is more specific and preferred, this parent term is technically accurate. Since the more specific term is already annotated, this broader annotation is acceptable as it provides correct hierarchical coverage. IEA annotations often propagate from broader InterPro signatures and this is consistent with the enzyme's function.
Supporting Evidence:
PMID:29075324
exo-acting cellobiohydrolases thread the cellulose molecule from its free cellulose chain end through a tunnel built by loop structures around the active site
|
|
GO:0005576
extracellular region
|
IEA
GO_REF:0000044 |
MODIFY |
Summary: CelK is a secreted protein that incorporates into the extracellular cellulosome complex via its dockerin domain. The signal peptide (residues 1-27) is cleaved upon secretion. Proteomics confirms CelK is abundant in cellulosome preparations from cellulose-grown cells.
Reason: While CelK is secreted to the extracellular region, a more specific cellular component annotation would be GO:0043263 (cellulosome), as CelK is a bona fide cellulosomal enzyme that integrates via dockerin-cohesin interactions. The cellulosome is a defined extracellular multi-enzyme complex in C. thermocellum.
Proposed replacements:
cellulosome
Supporting Evidence:
PMID:16127726
the cellobiohydrolases Cbh9A, Cel9K, Cel48S
PMID:17644599
exoglucanases CelS and CelK
|
|
GO:0005975
carbohydrate metabolic process
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: CelK participates in carbohydrate metabolism by degrading cellulose. This annotation is correct but extremely broad - CelK's specific role is in cellulose catabolism.
Reason: This is a very high-level biological process term that is technically accurate but provides minimal information. Since more specific BP annotations exist (GO:0030245 cellulose catabolic process), this broad term is acceptable as hierarchical context but not informative as a standalone annotation. IEA from InterPro is appropriate for this level of granularity.
|
|
GO:0008810
cellulase activity
|
IEA
GO_REF:0000002 |
MODIFY |
Summary: CelK has cellulase activity as a GH9 family enzyme. However, the GO definition of cellulase activity (GO:0008810) specifically refers to endohydrolysis, whereas CelK functions as a cellobiohydrolase (exo-acting, EC 3.2.1.91) releasing cellobiose from non-reducing ends.
Reason: GO:0008810 (cellulase activity) is defined as "catalysis of the endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose". CelK is classified as EC 3.2.1.91 (cellulose 1,4-beta-cellobiosidase), which is an exo-acting enzyme that releases cellobiose from the non-reducing ends. The correct annotation is GO:0016162 (cellulose 1,4-beta-cellobiosidase activity), which is already present in the annotation set.
Proposed replacements:
cellulose 1,4-beta-cellobiosidase activity
Supporting Evidence:
PMID:29075324
As expected, for the CBHs Cbh9A, Cel48S, and Cel9K no or very weak activities on modified substrates were observed, whereas on PASC substantial product formation was found
|
|
GO:0016162
cellulose 1,4-beta-cellobiosidase activity
|
IEA
GO_REF:0000003 |
ACCEPT |
Summary: This is the most accurate molecular function annotation for CelK. The enzyme is classified as EC 3.2.1.91 (cellulose 1,4-beta-cellobiosidase), which matches this GO term exactly. UniProt catalytic activity annotation confirms: "Hydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose and cellotetraose, releasing cellobiose from the non-reducing ends of the chains."
Reason: This is the correct and most specific molecular function annotation for CelK. The annotation is derived from EC:3.2.1.91 mapping, which is the experimentally determined enzyme classification for this protein. This represents the core catalytic function of CelK.
Supporting Evidence:
PMID:29075324
CBHs (exo-acting from the sugar ends) released specifically cellobiose as the only product over time (Cel48S, Cel9K, and Cbh9A)
|
|
GO:0016787
hydrolase activity
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: CelK is indeed a hydrolase - it catalyzes the hydrolytic cleavage of beta-1,4-glucosidic bonds. This annotation is correct but extremely general.
Reason: This is the root molecular function term for hydrolases. While technically accurate, it provides minimal information. More specific annotations (GO:0016162, GO:0004553, GO:0016798) are already present and preferred. This broad term is acceptable as it provides hierarchical consistency but is not informative as a standalone annotation.
|
|
GO:0016798
hydrolase activity, acting on glycosyl bonds
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: CelK hydrolyzes glycosyl bonds (specifically beta-1,4-glucosidic linkages in cellulose). This annotation is correct and at an appropriate intermediate level of specificity.
Reason: This term accurately describes CelK's molecular function at an intermediate level of specificity. While GO:0016162 is more specific, this parent term is correctly applied. IEA annotation from InterPro domain signatures appropriately captures this level of function.
|
|
GO:0030245
cellulose catabolic process
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: CelK is directly involved in cellulose catabolism as a major cellulosomal cellulase. The enzyme degrades crystalline cellulose to cellobiose and cellotriose as primary products. This is the most appropriate biological process annotation for CelK.
Reason: This is the correct and most specific biological process annotation for CelK. The enzyme's primary biological role is cellulose degradation as part of the cellulosome complex. This annotation accurately represents the core biological process in which CelK participates.
Supporting Evidence:
PMID:29075324
After prolonged incubation times (overnight), the final products are mainly cellobiose and cellotriose (DP 2 to DP 3)
|
|
GO:0043263
cellulosome
|
IEA
GO_REF:0000044 |
NEW |
Summary: CelK contains a C-terminal type I dockerin domain (residues 828-894) that mediates integration into the cellulosome via interaction with cohesin domains on the CipA scaffoldin protein. Proteomics confirms CelK is one of the most abundant cellulosomal enzyme subunits.
Reason: This annotation is not currently in the GOA file but is strongly supported by the domain architecture (dockerin domain) and proteomics data showing CelK as a major cellulosomal component. This is the most specific and accurate cellular component annotation.
Supporting Evidence:
PMID:17644599
exoglucanases CelS and CelK
PMID:16127726
the cellobiohydrolases Cbh9A, Cel9K, Cel48S
file:ACET2/celK/celK-deep-research-falcon.md
CelK is a secreted, extracellular cellulosomal subunit that incorporates into the cellulosome via type-I dockerin interactions
|
Q: What is the precise processivity of CelK - does it remain attached to the cellulose chain after each catalytic event or does it dissociate and rebind?
Suggested experts: Wolfgang H. Schwarz, Vladimir V. Zverlov
Q: What are the kinetic parameters (kcat, Km) for CelK on various cellulosic substrates (Avicel, PASC, CMC)?
Suggested experts: Benedikt Leis, Wolfgang Liebl
Experiment: Perform single-molecule fluorescence microscopy to track individual CelK molecules on cellulose nanocrystals. Measure processivity (number of catalytic events per encounter) and compare to other GH9 family members with known processivities.
Hypothesis: CelK exhibits processive cellobiohydrolase activity on crystalline cellulose
Type: Single-molecule enzymology
Experiment: Measure hydrolysis rates of crystalline cellulose (Avicel) using CelK alone, Cel48S alone, and equimolar combinations. Quantify synergy as the ratio of combined activity to the sum of individual activities. Test at various enzyme ratios to determine optimal stoichiometry.
Hypothesis: CelK and Cel48S show synergistic enhancement of cellulose hydrolysis
Type: Enzyme kinetics / synergy assay
provider: falcon
model: Edison Scientific Literature
cached: false
start_time: '2025-12-26T17:03:10.211136'
end_time: '2025-12-26T17:10:34.347651'
duration_seconds: 444.14
template_file: templates/gene_research_go_focused.md
template_variables:
organism: ACET2
gene_id: celK
gene_symbol: celK
uniprot_accession: A3DCH1
protein_description: 'RecName: Full=Cellulose 1,4-beta-cellobiosidase; EC=3.2.1.91;
Flags: Precursor;'
gene_info: Name=celK; OrderedLocusNames=Cthe_0412; ORFNames=CtheDRAFT_2165;
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 9 (cellulase E) family.
protein_domains: 6-hairpin_glycosidase_sf. (IPR008928); 6hp_glycosidase-like_sf.
(IPR012341); Cellulase_Ig-like. (IPR004197); CenC_carb-bd. (IPR003305); Dockerin_1_rpt.
(IPR002105)
provider_config:
timeout: 600
max_retries: 3
parameters:
allowed_domains: []
temperature: 0.1
citation_count: 27
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 'celK' 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 celK (gene ID: celK, UniProt: A3DCH1) 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 'celK' 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 celK (gene ID: celK, UniProt: A3DCH1) 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 celK from Acetivibrio thermocellus (Clostridium thermocellum). Comparative catalogs and proteomics explicitly map CelK to Cel9K with locus tag Cthe_0412 (also called Cel9K), confirming gene/protein identity in the correct organismal context (C. thermocellum ATCC 27405 lineage) (leis2017comparativecharacterizationof pages 7-8, munir2014comparativeanalysisof pages 13-13). Domain annotations from proteomics list CBM and dockerin modules consistent with a cellulosomal GH9 enzyme (zverlov2005functionalsubgenomicsof pages 2-4). No conflicting usage of โcelKโ in unrelated organisms was used for this report.
Comprehensive research report: celK (CelK; Cel9K; Cthe_0412) in Acetivibrio thermocellus
1) Key concepts and definitions
- Primary function and EC: CelK is a cellulase in the C. thermocellum cellulosome; literature treats CelK as a cellobiohydrolase (EC 3.2.1.91) and a major cellulosomal component involved in crystalline cellulose depolymerization to short cellodextrins, notably cellobiose (DP2) (Munir 2014, citing CelK as โa new cellobiohydrolaseโ and โmajor cellulosome componentโ) (https://doi.org/10.1371/journal.pone.0104260; published Aug 2014) (munir2014comparativeanalysisof pages 13-13). Comparative analyses of all cellulosomal cellulases position Cel9K in GH9 and define catalytic behaviors of GH9 enzymes, including processive endoglucanase modes that yield cellobiose/cellotriose (DP2โ3) (https://doi.org/10.1186/s13068-017-0928-4; published Oct 2017) (leis2017comparativecharacterizationof pages 1-2, leis2017comparativecharacterizationof pages 7-8).
- Enzyme class/family and mechanism: CelK belongs to glycoside hydrolase family 9 (GH9), which utilize an inverting catalytic mechanism. GH9 cellulases in C. thermocellum encompass exo-acting and processive endoglucanase behaviors, producing characteristic product spectra in controlled assays (https://doi.org/10.1186/s13068-017-0928-4; Oct 2017) (leis2017comparativecharacterizationof pages 1-2).
- Domain architecture: Proteomic/proteomic-informed domain mapping lists CelK among major cellulosomal components and assigns a modular architecture typical of cellulosomal GH9s, including a catalytic GH9 domain with carbohydrate-binding and Ig-like modules and a C-terminal dockerin (e.g., โCBM4-Ig-GH9-Doc1โ entry for CelK in proteomics table), consistent with extracellular cellulosome incorporation (https://doi.org/10.1002/pmic.200401199; Sep 2005) (zverlov2005functionalsubgenomicsof pages 2-4). GH9 cellulases in C. thermocellum frequently carry CBM3 variants (e.g., CelI GH9 with CBM3c/CBM3b) that enhance chain feeding/binding and processivity on crystalline cellulose, serving as a mechanistic analogue for GH9 domain function (https://doi.org/10.1128/jb.185.2.391-398.2003; Jan 2003) (gilad2003celianoncellulosomal pages 1-2).
- Cellular/extracellular localization: CelK is a secreted, extracellular cellulosomal subunit that incorporates into the cellulosome via type-I dockerin interactions, contributing to surface-associated cellulose degradation (https://doi.org/10.1186/s13068-017-0928-4; Oct 2017) (leis2017comparativecharacterizationof pages 7-8, gold2007proteomicanalysisof pages 65-68, zverlov2005functionalsubgenomicsof pages 2-4, gold2007proteomicanalysisof pages 68-69).
2) Recent developments and latest research (emphasis 2023โ2024)
- System-level context: Recent work underscores synergy between GH9 and GH48 cellulases in cellulosomal systems, where GH48 cellobiohydrolases (e.g., Cel48S/CelS) synergize strongly with GH9 enzymes to drive cellulose deconstruction; this is a current focus for biocatalyst engineering (https://doi.org/10.3390/fermentation9030204; Feb 2023) (gold2007proteomicanalysisof pages 68-69). Comparative catalogs (although 2017) remain the most comprehensive reference to the complete set of C. thermocellum cellulosomal cellulases and their hydrolysis modes, informing ongoing 2023โ2024 engineering of enzyme mixtures and designer cellulosomes (https://doi.org/10.1186/s13068-017-0928-4; Oct 2017) (leis2017comparativecharacterizationof pages 1-2, leis2017comparativecharacterizationof pages 7-8). While 2023โ2024 reviews advance broader cellulosome engineering strategies, CelK-specific new kinetic or structural determinations were not found in 2023โ2024; thus, CelKโs current understanding still relies on the definitive proteomics and comparative functional studies cited below.
3) Current applications and real-world implementations
- Biomass deconstruction platforms: In designer miniโcellulosomes, combining GH9 representatives with Cel48S (GH48) maximizes hydrolytic performance on cellulose; artificial nonavalent cellulosomes recovered ~50% of native cellulosome activity, highlighting the operational role of GH9 (including CelK) in practical enzyme cocktails and consolidated bioprocessing concepts (https://doi.org/10.1186/s13068-017-0928-4; Oct 2017) (leis2017comparativecharacterizationof pages 1-2). Reviews on GH48-GH9 synergy emphasize deploying GH9 cellulases alongside GH48 in biorefinery-relevant contexts (https://doi.org/10.3390/fermentation9030204; Feb 2023) (gold2007proteomicanalysisof pages 68-69).
4) Expert opinions and analysis from authoritative sources
- Role vis-ร -vis Cel48S (CelS): Quantitative proteomics and comparative enzymology position CelK (Cel9K) as a prominent GH9 partner to Cel48S. Leis et al. explicitly list Cel48S/Cel9K as a basic functional pairing in the cellulosome; product analyses at 60ยฐC and pH 5.8 show soluble final products dominated by DP2โ3 (cellobiose/cellotriose), consistent with GH48+GH9 synergy (https://doi.org/10.1186/s13068-017-0928-4; Oct 2017) (leis2017comparativecharacterizationof pages 7-8). Proteomics ranks CelK among the most abundant enzymatic subunits of the cellulosome under cellulose or cellobiose growth, comparable in magnitude to Cel48S depending on substrate, supporting a model in which CelK contributes processive chain cleavage complementing Cel48Sโs reducing-end exo activity (https://doi.org/10.1128/jb.00882-07; Oct 2007) (gold2007globalviewof pages 8-9, gold2007proteomicanalysisof pages 65-68, gold2007proteomicanalysisof pages 68-69).
5) Relevant statistics and data
- Enzyme set and assay conditions: The comprehensive comparative study tested all 24 single cellulosomal cellulases under identical conditions, defining four hydrolysis modes and product spectra. Product TLC heatmaps showed DP2โ3 products predominate after overnight reactions at 60ยฐC, pH 5.8 with model and cellulosic substrates, situating Cel9K within the GH9 group that contributes these product patterns (https://doi.org/10.1186/s13068-017-0928-4; Oct 2017) (leis2017comparativecharacterizationof pages 1-2, leis2017comparativecharacterizationof pages 7-8).
- Proteomic abundance (cellulose-grown): In Avicel-grown cellulosomes, CelK (GH9) is a major component. One proteomic table reports CelK with 39 unique peptide observations, emPAI 4.12, dockerin I/CipA mol% ~11.0, coverage ~35%, versus Cel48S with 29 peptides, emPAI 3.56, DocI/CipA mol% ~9.4, coverage ~32%โall consistent with high abundance of both subunits; CipA scaffold ranked highest (emPAI 5.92) (Gold 2007; details from the table) (gold2007proteomicanalysisof pages 65-68). Under cellobiose growth, CelK remained abundant with emPAI 1.12 and normalized abundance ~0.52 relative to CipA (Gold 2007; table legend explains emPAI and normalization) (gold2007proteomicanalysisof pages 68-69). A separate proteomic study identified CelK and Cel48S among the 13 major cellulosomal components on 2โD gels of cellulose-grown cellulosomes and reported approximate abundances (Zverlov 2005) (https://doi.org/10.1002/pmic.200401199; Sep 2005) (zverlov2005functionalsubgenomicsof pages 2-4, zverlov2005functionalsubgenomicsof pages 1-2).
- Domain mapping evidence: The proteomics catalog lists CelK with CBM and Ig-like repeats plus GH9โdockerin, e.g., โCBM4โIgโGH9โDoc1,โ consistent with an extracellular cellulosomal GH9 architecture (Zverlov 2005) (https://doi.org/10.1002/pmic.200401199; Sep 2005) (zverlov2005functionalsubgenomicsof pages 2-4). GH9 architecture-function relations are supported by GH9 exemplars such as CelI (GH9 with CBM3c/CBM3b) showing processive endoglucanase activity on crystalline cellulose (https://doi.org/10.1128/jb.185.2.391-398.2003; Jan 2003) (gilad2003celianoncellulosomal pages 1-2).
Mechanistic synthesis: reaction, specificity, localization, and pathway role
- Reaction and specificity: CelK (GH9) acts on ฮฒ-1,4-linked glucans of cellulose, contributing both processive chain cleavage and cellobiohydrolase-like activity within the cellulosome, releasing short cello-oligosaccharides (DP2โ3; predominantly cellobiose) under standard assay conditions (60ยฐC, pH ~5.8) (https://doi.org/10.1186/s13068-017-0928-4; Oct 2017) (leis2017comparativecharacterizationof pages 1-2, leis2017comparativecharacterizationof pages 7-8). Literature explicitly labels CelK as a cellobiohydrolase and as a major cellulosomal enzyme (Munir 2014) (https://doi.org/10.1371/journal.pone.0104260; Aug 2014) (munir2014comparativeanalysisof pages 13-13).
- Domain-context inference: Proteomics domain mapping places CelK as a modular GH9 with CBM(s), Ig-like repeats, and a C-terminal dockerin (Doc1), explaining its incorporation into the cellulosome and its functionality on ordered cellulose through enhanced substrate targeting and chain feeding (https://doi.org/10.1002/pmic.200401199; Sep 2005) (zverlov2005functionalsubgenomicsof pages 2-4), in line with GH9 exemplars (https://doi.org/10.1128/jb.185.2.391-398.2003; Jan 2003) (gilad2003celianoncellulosomal pages 1-2).
- Localization and pathway: CelK is extracellular and cell-surface-associated via the cellulosome, operating in concert with Cel48S (GH48) and other cellulases to hydrolyze cellulose to cellodextrins that feed into downstream uptake/fermentation pathways of C. thermocellum (https://doi.org/10.1186/s13068-017-0928-4; Oct 2017) (leis2017comparativecharacterizationof pages 7-8). Proteomics consistently detects CelK at high abundance in cellulosome preparations from cellulose/cellobiose growth (https://doi.org/10.1128/jb.00882-07; Oct 2007; https://doi.org/10.1002/pmic.200401199; Sep 2005) (gold2007proteomicanalysisof pages 65-68, zverlov2005functionalsubgenomicsof pages 2-4, gold2007proteomicanalysisof pages 68-69).
- Role relative to Cel48S (CelS): Cel48S is the dominant GH48 exoglucanase operating from reducing ends; CelK (GH9) provides complementary chain cleavage/processivity and is explicitly paired with Cel48S in basic complexes, supporting synergistic cellulose hydrolysis where diverse processivities are necessary for high cellulosome efficiency (https://doi.org/10.1186/s13068-017-0928-4; Oct 2017; https://doi.org/10.3390/fermentation9030204; Feb 2023) (leis2017comparativecharacterizationof pages 7-8, gold2007proteomicanalysisof pages 68-69).
Limitations and open points
- Kinetic parameters: Within the provided excerpts, detailed kcat/Km values for CelK were not reported. Available data include comparative activity/product profiles and proteomic abundance; readers requiring explicit kinetics should consult targeted biochemical characterizations not captured in the retrieved excerpts (leis2017comparativecharacterizationof pages 1-2, leis2017comparativecharacterizationof pages 7-8).
Embedded evidence summary
| Attribute | Evidence summary | Source |
|---|---|---|
| Identity mapping (CelK = Cel9K = Cthe_0412) | CelK is listed as Cel9K (locus Cthe_0412) in comparative catalogs of C. thermocellum cellulosomal enzymes, linking the gene symbol CelK to the GH9 cellulosomal enzyme. | Leis et al., 2017 https://doi.org/10.1186/s13068-017-0928-4; Munir et al., 2014 https://doi.org/10.1371/journal.pone.0104260 (leis2017comparativecharacterizationof pages 7-8, munir2014comparativeanalysisof pages 13-13) |
| Enzyme class and EC | Described in the literature as a cellulase with cellobiohydrolase-like role within the cellulosome; UniProt/earlier reports annotate CelK as a cellobiohydrolase (EC 3.2.1.91), and Munir reports CelK as a major cellulosome component/new cellobiohydrolase. | Munir et al., 2014 https://doi.org/10.1371/journal.pone.0104260; Leis et al., 2017 https://doi.org/10.1186/s13068-017-0928-4 (munir2014comparativeanalysisof pages 13-13, leis2017comparativecharacterizationof pages 7-8) |
| GH family and mechanism (GH9) | Assigned to glycoside hydrolase family 9 (GH9); GH9 enzymes use an inverting mechanism and show diversity in processivity (including processive endoglucanase behaviors that can produce cellobiose intermediates). | Leis et al., 2017 https://doi.org/10.1186/s13068-017-0928-4 (leis2017comparativecharacterizationof pages 1-2) |
| Domain architecture (catalytic GH9; CBMs/Ig-like/dockerin inferred) | Excerpts do not give a complete CelK domain map in these texts; GH9 catalytic domain plus cellulose-binding modules (e.g., CBM3 variants), Ig-like repeats and a dockerin are typical for cellulosomal GH9s โ inference supported by detailed GH9 examples (e.g., CelI) and the cellulosomal context. | Gilad et al., 2003 https://doi.org/10.1128/jb.185.2.391-398.2003; Leis et al., 2017 https://doi.org/10.1186/s13068-017-0928-4 (gilad2003celianoncellulosomal pages 1-2, leis2017comparativecharacterizationof pages 7-8) |
| Cellular/extracellular localization | CelK is a cellulosomal (extracellular, cell-surface-associated) enzyme incorporated via dockerinโcohesin interactions into the cellulosome complex. | Leis et al., 2017 https://doi.org/10.1186/s13068-017-0928-4 (leis2017comparativecharacterizationof pages 7-8) |
| Functional role relative to Cel48S (CelS) | Leis et al. list "Cel48S/Cel9K" as a basic partner pairing; Cel48S (a GH48 exo-cellobiohydrolase) acts primarily from the reducing end while Cel9K (GH9) provides complementary cleavage/processivity producing DP2โ3 products, so the two act synergistically in the cellulosome. | Leis et al., 2017 https://doi.org/10.1186/s13068-017-0928-4 (leis2017comparativecharacterizationof pages 7-8) |
| Substrate specificity and products | Active on cellulosic substrates (e.g., PASC, Avicel); product analysis in comparative assays shows final soluble products after extended hydrolysis are mainly cellobiose and cellotriose (DP2โ3). | Leis et al., 2017 https://doi.org/10.1186/s13068-017-0928-4 (leis2017comparativecharacterizationof pages 7-8) |
| Activity conditions reported in comparative assays | Comparative assays in Leis et al. were performed under cellulosome-relevant conditions (~60ยฐC, pH ~5.8), which were used for product/profile analyses. | Leis et al., 2017 https://doi.org/10.1186/s13068-017-0928-4 (leis2017comparativecharacterizationof pages 7-8) |
| Proteomic detection / abundance | Catalogs and proteomic/functional surveys list CelK among major cellulosomal cellulases, indicating it is a prominent extracellular component in C. thermocellum cellulosomes. | Munir et al., 2014 https://doi.org/10.1371/journal.pone.0104260; Leis et al., 2017 https://doi.org/10.1186/s13068-017-0928-4 (munir2014comparativeanalysisof pages 13-13, leis2017comparativecharacterizationof pages 7-8) |
| Kinetics / quantitative data hints | Leis et al. report measured activity values (relative activities/product profiles) for Cel9K in comparative tables but do not provide full kinetic parameters (kcat/Km) in the provided excerpts; explicit detailed kinetics appear absent from these excerpts. | Leis et al., 2017 https://doi.org/10.1186/s13068-017-0928-4 (leis2017comparativecharacterizationof pages 7-8, leis2017comparativecharacterizationof pages 1-2) |
Table: Concise, cited evidence summarizing identity, classification, domain inferences, localization, role with Cel48S, substrates/products, assay conditions, proteomic presence, and data availability for CelK (Cel9K; Cthe_0412). This table helps quickly map major claims to their source excerpts.
References with URLs and publication dates
- Leis B. et al. Comparative characterization of all cellulosomal cellulases from Clostridium thermocellum. Biotechnology for Biofuels, Oct 2017. https://doi.org/10.1186/s13068-017-0928-4 (leis2017comparativecharacterizationof pages 2-4, leis2017comparativecharacterizationof pages 1-2, leis2017comparativecharacterizationof pages 7-8)
- Gilad R. et al. CelI, a noncellulosomal family 9 enzyme from Clostridium thermocellum, is a processive endoglucanase. Journal of Bacteriology, Jan 2003. https://doi.org/10.1128/jb.185.2.391-398.2003 (gilad2003celianoncellulosomal pages 1-2)
- Munir R.I. et al. Comparative analysis of CAZymes in Clostridium termitidis CT1112 (discussion citing CelK as new cellobiohydrolase and major component in C. thermocellum). PLoS ONE, Aug 2014. https://doi.org/10.1371/journal.pone.0104260 (munir2014comparativeanalysisof pages 13-13)
- Zverlov V.V. et al. Functional subgenomics of C. thermocellum cellulosomal genes: major components and new enzymes. PROTEOMICS, Sep 2005. https://doi.org/10.1002/pmic.200401199 (zverlov2005functionalsubgenomicsof pages 2-4, zverlov2005functionalsubgenomicsof pages 1-2)
- Gold N.D., Martin V.J.J. Global view of the C. thermocellum cellulosome revealed by quantitative proteomics. Journal of Bacteriology, Oct 2007. https://doi.org/10.1128/jb.00882-07 (gold2007globalviewof pages 8-9)
- Gold N. Proteomic analysis of the C. thermocellum cellulosome (tables with emPAI for CelK/Cel48S under Avicel or cellobiose). 2007. (See extracted table summaries) (gold2007proteomicanalysisof pages 65-68, gold2007proteomicanalysisof pages 68-69)
- You C. et al. GH48 cellulase: key player in cellulolytic bacteria for lignocellulose biorefinery. Fermentation, Feb 2023. https://doi.org/10.3390/fermentation9030204 (gold2007proteomicanalysisof pages 68-69)
References
(leis2017comparativecharacterizationof pages 7-8): Benedikt Leis, Claudia Held, Fabian Bergkemper, Katharina Dennemarck, Robert Steinbauer, Alarich Reiter, Matthias Mechelke, Matthias Moerch, Sigrid Graubner, Wolfgang Liebl, Wolfgang H. Schwarz, and Vladimir V. Zverlov. Comparative characterization of all cellulosomal cellulases from clostridium thermocellum reveals high diversity in endoglucanase product formation essential for complex activity. Biotechnology for Biofuels, Oct 2017. URL: https://doi.org/10.1186/s13068-017-0928-4, doi:10.1186/s13068-017-0928-4. This article has 63 citations.
(munir2014comparativeanalysisof pages 13-13): Riffat I. Munir, John Schellenberg, Bernard Henrissat, Tobin J. Verbeke, Richard Sparling, and David B. Levin. Comparative analysis of carbohydrate active enzymes in clostridium termitidis ct1112 reveals complex carbohydrate degradation ability. PLoS ONE, 9:e104260, Aug 2014. URL: https://doi.org/10.1371/journal.pone.0104260, doi:10.1371/journal.pone.0104260. This article has 43 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.
(leis2017comparativecharacterizationof pages 1-2): Benedikt Leis, Claudia Held, Fabian Bergkemper, Katharina Dennemarck, Robert Steinbauer, Alarich Reiter, Matthias Mechelke, Matthias Moerch, Sigrid Graubner, Wolfgang Liebl, Wolfgang H. Schwarz, and Vladimir V. Zverlov. Comparative characterization of all cellulosomal cellulases from clostridium thermocellum reveals high diversity in endoglucanase product formation essential for complex activity. Biotechnology for Biofuels, Oct 2017. URL: https://doi.org/10.1186/s13068-017-0928-4, doi:10.1186/s13068-017-0928-4. This article has 63 citations.
(gilad2003celianoncellulosomal pages 1-2): Rachel Gilad, Larisa Rabinovich, Sima Yaron, Edward A. Bayer, Raphael Lamed, Harry J. Gilbert, and Yuval Shoham. Celi, a noncellulosomal family 9 enzyme from clostridium thermocellum, is a processive endoglucanase that degrades crystalline cellulose. Journal of Bacteriology, 185:391-398, Jan 2003. URL: https://doi.org/10.1128/jb.185.2.391-398.2003, doi:10.1128/jb.185.2.391-398.2003. This article has 165 citations and is from a peer-reviewed journal.
(gold2007proteomicanalysisof pages 65-68): N Gold. Proteomic analysis of the clostridium thermocellum cellulosome. Unknown journal, 2007.
(gold2007proteomicanalysisof pages 68-69): N Gold. Proteomic analysis of the clostridium thermocellum cellulosome. Unknown journal, 2007.
(gold2007globalviewof pages 8-9): 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.
(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.
(leis2017comparativecharacterizationof pages 2-4): Benedikt Leis, Claudia Held, Fabian Bergkemper, Katharina Dennemarck, Robert Steinbauer, Alarich Reiter, Matthias Mechelke, Matthias Moerch, Sigrid Graubner, Wolfgang Liebl, Wolfgang H. Schwarz, and Vladimir V. Zverlov. Comparative characterization of all cellulosomal cellulases from clostridium thermocellum reveals high diversity in endoglucanase product formation essential for complex activity. Biotechnology for Biofuels, Oct 2017. URL: https://doi.org/10.1186/s13068-017-0928-4, doi:10.1186/s13068-017-0928-4. This article has 63 citations.
---
id: A3DCH1
gene_symbol: celK
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: CelK (also known as Cel9K, locus Cthe_0412) is a major cellulosomal cellulase
belonging to glycoside hydrolase family 9 (GH9) in Acetivibrio thermocellus (formerly
Clostridium thermocellum). It functions as a cellulose 1,4-beta-cellobiosidase (EC
3.2.1.91) that hydrolyzes beta-1,4-glucosidic linkages in cellulose, releasing cellobiose
and cellotriose from the non-reducing ends of cellulose chains. The enzyme has a
modular architecture consisting of a CBM4 carbohydrate-binding module, an Ig-like
domain, the GH9 catalytic domain, and a C-terminal type I dockerin domain that mediates
integration into the cellulosome complex. CelK works synergistically with Cel48S
(the major GH48 cellobiohydrolase) in the cellulosome to efficiently degrade crystalline
cellulose.
existing_annotations:
- term:
id: GO:0000272
label: polysaccharide catabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: CelK is a cellulase that degrades cellulose, which is a polysaccharide.
The annotation to polysaccharide catabolic process is correct but overly broad.
CelK specifically catalyzes the breakdown of cellulose (a beta-1,4-glucan),
not polysaccharides in general.
action: MODIFY
reason: While cellulose is a polysaccharide and CelK does participate in polysaccharide
catabolism, this term is too general. The more specific term GO:0030245 (cellulose
catabolic process) already exists in the annotation set and accurately captures
the biological process. This broader term provides less informative annotation.
proposed_replacement_terms:
- id: GO:0030245
label: cellulose catabolic process
additional_reference_ids:
- PMID:29075324
- file:ACET2/celK/celK-deep-research-falcon.md
supported_by:
- reference_id: PMID:29075324
supporting_text: CBHs (exo-acting from the sugar ends) released specifically
cellobiose as the only product over time (Cel48S, Cel9K, and Cbh9A)
- term:
id: GO:0004553
label: hydrolase activity, hydrolyzing O-glycosyl compounds
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: CelK is a GH9 family glycoside hydrolase that hydrolyzes beta-1,4-glucosidic
bonds in cellulose. This annotation is correct but too general - the enzyme
has specific cellobiohydrolase activity (EC 3.2.1.91) rather than generic
glycosyl hydrolase activity.
action: ACCEPT
reason: While GO:0016162 (cellulose 1,4-beta-cellobiosidase activity) is more
specific and preferred, this parent term is technically accurate. Since the
more specific term is already annotated, this broader annotation is acceptable
as it provides correct hierarchical coverage. IEA annotations often propagate
from broader InterPro signatures and this is consistent with the enzyme's
function.
additional_reference_ids: [file:ACET2/celK/celK-deep-research-falcon.md]
supported_by:
- reference_id: PMID:29075324
supporting_text: exo-acting cellobiohydrolases thread the cellulose molecule
from its free cellulose chain end through a tunnel built by loop structures
around the active site
- term:
id: GO:0005576
label: extracellular region
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: CelK is a secreted protein that incorporates into the extracellular
cellulosome complex via its dockerin domain. The signal peptide (residues
1-27) is cleaved upon secretion. Proteomics confirms CelK is abundant in cellulosome
preparations from cellulose-grown cells.
action: MODIFY
reason: While CelK is secreted to the extracellular region, a more specific
cellular component annotation would be GO:0043263 (cellulosome), as CelK is
a bona fide cellulosomal enzyme that integrates via dockerin-cohesin interactions.
The cellulosome is a defined extracellular multi-enzyme complex in C. thermocellum.
proposed_replacement_terms:
- id: GO:0043263
label: cellulosome
additional_reference_ids:
- PMID:16127726
- PMID:17644599
- file:ACET2/celK/celK-deep-research-falcon.md
supported_by:
- reference_id: PMID:16127726
supporting_text: the cellobiohydrolases Cbh9A, Cel9K, Cel48S
- reference_id: PMID:17644599
supporting_text: exoglucanases CelS and CelK
- term:
id: GO:0005975
label: carbohydrate metabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: CelK participates in carbohydrate metabolism by degrading cellulose.
This annotation is correct but extremely broad - CelK's specific role is in
cellulose catabolism.
action: ACCEPT
reason: This is a very high-level biological process term that is technically
accurate but provides minimal information. Since more specific BP annotations
exist (GO:0030245 cellulose catabolic process), this broad term is acceptable
as hierarchical context but not informative as a standalone annotation. IEA
from InterPro is appropriate for this level of granularity.
additional_reference_ids: [file:ACET2/celK/celK-deep-research-falcon.md]
- term:
id: GO:0008810
label: cellulase activity
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: CelK has cellulase activity as a GH9 family enzyme. However, the GO
definition of cellulase activity (GO:0008810) specifically refers to endohydrolysis,
whereas CelK functions as a cellobiohydrolase (exo-acting, EC 3.2.1.91) releasing
cellobiose from non-reducing ends.
action: MODIFY
reason: GO:0008810 (cellulase activity) is defined as "catalysis of the endohydrolysis
of (1->4)-beta-D-glucosidic linkages in cellulose". CelK is classified as
EC 3.2.1.91 (cellulose 1,4-beta-cellobiosidase), which is an exo-acting enzyme
that releases cellobiose from the non-reducing ends. The correct annotation
is GO:0016162 (cellulose 1,4-beta-cellobiosidase activity), which is already
present in the annotation set.
proposed_replacement_terms:
- id: GO:0016162
label: cellulose 1,4-beta-cellobiosidase activity
additional_reference_ids:
- PMID:29075324
- file:ACET2/celK/celK-deep-research-falcon.md
supported_by:
- reference_id: PMID:29075324
supporting_text: As expected, for the CBHs Cbh9A, Cel48S, and Cel9K no or
very weak activities on modified substrates were observed, whereas on
PASC substantial product formation was found
- term:
id: GO:0016162
label: cellulose 1,4-beta-cellobiosidase activity
evidence_type: IEA
original_reference_id: GO_REF:0000003
review:
summary: 'This is the most accurate molecular function annotation for CelK.
The enzyme is classified as EC 3.2.1.91 (cellulose 1,4-beta-cellobiosidase),
which matches this GO term exactly. UniProt catalytic activity annotation
confirms: "Hydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose and
cellotetraose, releasing cellobiose from the non-reducing ends of the chains."'
action: ACCEPT
reason: This is the correct and most specific molecular function annotation
for CelK. The annotation is derived from EC:3.2.1.91 mapping, which is the
experimentally determined enzyme classification for this protein. This represents
the core catalytic function of CelK.
additional_reference_ids:
- PMID:29075324
- file:ACET2/celK/celK-deep-research-falcon.md
supported_by:
- reference_id: PMID:29075324
supporting_text: CBHs (exo-acting from the sugar ends) released specifically
cellobiose as the only product over time (Cel48S, Cel9K, and Cbh9A)
- term:
id: GO:0016787
label: hydrolase activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: CelK is indeed a hydrolase - it catalyzes the hydrolytic cleavage of
beta-1,4-glucosidic bonds. This annotation is correct but extremely general.
action: ACCEPT
reason: This is the root molecular function term for hydrolases. While technically
accurate, it provides minimal information. More specific annotations (GO:0016162,
GO:0004553, GO:0016798) are already present and preferred. This broad term
is acceptable as it provides hierarchical consistency but is not informative
as a standalone annotation.
additional_reference_ids: [file:ACET2/celK/celK-deep-research-falcon.md]
- term:
id: GO:0016798
label: hydrolase activity, acting on glycosyl bonds
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: CelK hydrolyzes glycosyl bonds (specifically beta-1,4-glucosidic linkages
in cellulose). This annotation is correct and at an appropriate intermediate
level of specificity.
action: ACCEPT
reason: This term accurately describes CelK's molecular function at an intermediate
level of specificity. While GO:0016162 is more specific, this parent term
is correctly applied. IEA annotation from InterPro domain signatures appropriately
captures this level of function.
additional_reference_ids: [file:ACET2/celK/celK-deep-research-falcon.md]
- term:
id: GO:0030245
label: cellulose catabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: CelK is directly involved in cellulose catabolism as a major cellulosomal
cellulase. The enzyme degrades crystalline cellulose to cellobiose and cellotriose
as primary products. This is the most appropriate biological process annotation
for CelK.
action: ACCEPT
reason: This is the correct and most specific biological process annotation
for CelK. The enzyme's primary biological role is cellulose degradation as
part of the cellulosome complex. This annotation accurately represents the
core biological process in which CelK participates.
additional_reference_ids:
- PMID:29075324
- file:ACET2/celK/celK-deep-research-falcon.md
supported_by:
- reference_id: PMID:29075324
supporting_text: After prolonged incubation times (overnight), the final
products are mainly cellobiose and cellotriose (DP 2 to DP 3)
- term:
id: GO:0043263
label: cellulosome
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: CelK contains a C-terminal type I dockerin domain (residues 828-894)
that mediates integration into the cellulosome via interaction with cohesin
domains on the CipA scaffoldin protein. Proteomics confirms CelK is one of
the most abundant cellulosomal enzyme subunits.
action: NEW
reason: This annotation is not currently in the GOA file but is strongly supported
by the domain architecture (dockerin domain) and proteomics data showing CelK
as a major cellulosomal component. This is the most specific and accurate
cellular component annotation.
additional_reference_ids:
- PMID:17644599
- PMID:16127726
- file:ACET2/celK/celK-deep-research-falcon.md
supported_by:
- reference_id: PMID:17644599
supporting_text: exoglucanases CelS and CelK
- reference_id: PMID:16127726
supporting_text: the cellobiohydrolases Cbh9A, Cel9K, Cel48S
- reference_id: file:ACET2/celK/celK-deep-research-falcon.md
supporting_text: CelK is a secreted, extracellular cellulosomal subunit
that incorporates into the cellulosome via type-I dockerin interactions
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:0000044
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
vocabulary mapping, accompanied by conservative changes to GO terms applied
by UniProt
findings: []
- id: GO_REF:0000120
title: Combined Automated Annotation using Multiple IEA Methods
findings: []
- id: PMID:29075324
title: Comparative characterization of all cellulosomal cellulases from Clostridium
thermocellum
findings:
- statement: Cel9K is classified as a cellobiohydrolase (CBH) in Table 1
supporting_text: Cel9K0412GH9Inverting
- statement: CBHs including Cel9K release cellobiose as the main product
supporting_text: CBHs (exo-acting from the sugar ends) released specifically
cellobiose as the only product over time (Cel48S, Cel9K, and Cbh9A)
- statement: Cel9K shows weak activity on modified substrates but substantial
activity on PASC
supporting_text: As expected, for the CBHs Cbh9A, Cel48S, and Cel9K no or
very weak activities on modified substrates were observed, whereas on PASC
substantial product formation was found
- id: PMID:16127726
title: Functional subgenomics of Clostridium thermocellum cellulosomal genes
findings:
- statement: Cel9K is identified as a major cellulosomal cellobiohydrolase
supporting_text: the cellobiohydrolases Cbh9A, Cel9K, Cel48S
- id: PMID:17644599
title: Global view of the Clostridium thermocellum cellulosome revealed by quantitative
proteomic analysis
findings:
- statement: CelK shows higher expression in cellulosomes from cellulose-grown
cells
supporting_text: exoglucanases CelS and CelK
- id: file:ACET2/celK/celK-deep-research-falcon.md
title: Deep research literature review for celK
findings:
- statement: CelK identity confirmed as Cel9K with locus Cthe_0412
supporting_text: The target is celK from Acetivibrio thermocellus (Clostridium
thermocellum). Comparative catalogs and proteomics explicitly map CelK to
Cel9K with locus tag Cthe_0412
- statement: CelK is a cellulosomal subunit with type-I dockerin
supporting_text: CelK is a secreted, extracellular cellulosomal subunit that
incorporates into the cellulosome via type-I dockerin interactions
- statement: CelK belongs to GH9 family with inverting mechanism
supporting_text: CelK belongs to glycoside hydrolase family 9 (GH9), which
utilize an inverting catalytic mechanism
core_functions:
- description: CelK functions as a cellulose 1,4-beta-cellobiosidase that hydrolyzes
beta-1,4-glucosidic linkages in crystalline cellulose, releasing cellobiose
from the non-reducing ends of cellulose chains. It operates as a component of
the cellulosome complex, working synergistically with Cel48S (GH48) to efficiently
degrade plant cell wall polysaccharides.
molecular_function:
id: GO:0016162
label: cellulose 1,4-beta-cellobiosidase activity
directly_involved_in:
- id: GO:0030245
label: cellulose catabolic process
locations:
- id: GO:0043263
label: cellulosome
substrates:
- id: CHEBI:18246
label: cellulose
supported_by:
- reference_id: PMID:29075324
supporting_text: CBHs (exo-acting from the sugar ends) released specifically
cellobiose as the only product over time (Cel48S, Cel9K, and Cbh9A)
suggested_questions:
- question: What is the precise processivity of CelK - does it remain attached to
the cellulose chain after each catalytic event or does it dissociate and rebind?
experts: [Wolfgang H. Schwarz, Vladimir V. Zverlov]
- question: What are the kinetic parameters (kcat, Km) for CelK on various cellulosic
substrates (Avicel, PASC, CMC)?
experts: [Benedikt Leis, Wolfgang Liebl]
suggested_experiments:
- hypothesis: CelK exhibits processive cellobiohydrolase activity on crystalline
cellulose
description: Perform single-molecule fluorescence microscopy to track individual
CelK molecules on cellulose nanocrystals. Measure processivity (number of catalytic
events per encounter) and compare to other GH9 family members with known processivities.
experiment_type: Single-molecule enzymology
- hypothesis: CelK and Cel48S show synergistic enhancement of cellulose hydrolysis
description: Measure hydrolysis rates of crystalline cellulose (Avicel) using
CelK alone, Cel48S alone, and equimolar combinations. Quantify synergy as the
ratio of combined activity to the sum of individual activities. Test at various
enzyme ratios to determine optimal stoichiometry.
experiment_type: Enzyme kinetics / synergy assay
tags: [cellulosome]