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MetaCyc Enzyme: cellulase G

Gene: celG Accession Numbers: G-12690 (MetaCyc), Cthe_2872

Synonyms: endoglucanase G

Species: Ruminiclostridium thermocellum ATCC 27405

Component of:
fully loaded scaffoldin (cellobiose, medium abundance catalytic subunits) (summary available)
cellulosome complex (or2p anchor, 18 most abundant catalytic units in cellobiose-grown cells) (extended summary available)

Summary:
Cellulase G is an endoglucanase of Ruminiclostridium thermocellum that belongs to the glycosyl hydrolase 5 family (formerly clellulase A class).

The celG gene was first cloned in a study where ten distinct EcoRI fragments of Clostridium thermocellum, corresponding to seven different endoglucanases, were cloned in Escherichia coli and shown to express enzymatic activities related to cellulose degradation [Millet85]. The gene conferred on Escherichia coli the ability to hydrolyse both carboxymethyl cellulose and 2'-chloro-4'-nitrophenyl-β-D-cellobioside (CNPC) [Hazlewood88].

The nucleotide sequence was subsequently determined [Lemaire93]. The N terminus of the enzyme contains a typical signal peptide, and the carboxy terminus contains a type I dockerin domain that facilitates its binding to one of the type I cohesin domains of the CipA scaffoldin protein, enabling it to become a part of the cellulosome complex [Lemaire93].

The recombinant protein was purified from Escherichia coli and used to raise an antiserum. The antiserum reacted with an immunoreactive polypeptide of 66 kDa, which was associated with the Ruminiclostridium thermocellum cellulosome [Lemaire93].

Locations: extracellular space

Molecular Weight of Polypeptide: 63.199 kD (from nucleotide sequence)

Unification Links: Entrez-gene:4809152 , Protein Model Portal:Q05332 , SMR:Q05332 , String:203119.Cthe_2872 , UniProt:Q05332

Relationship Links: CAZy:IN-FAMILY:GH5 , InterPro:IN-FAMILY:IPR001547 , InterPro:IN-FAMILY:IPR002105 , InterPro:IN-FAMILY:IPR013781 , InterPro:IN-FAMILY:IPR016134 , InterPro:IN-FAMILY:IPR017853 , InterPro:IN-FAMILY:IPR018087 , InterPro:IN-FAMILY:IPR018242 , InterPro:IN-FAMILY:IPR018247 , Pfam:IN-FAMILY:PF00150 , Pfam:IN-FAMILY:PF00404 , Prosite:IN-FAMILY:PS00018 , Prosite:IN-FAMILY:PS00448 , Prosite:IN-FAMILY:PS00659

Gene-Reaction Schematic: ?

GO Terms:

Cellular Component: GO:0005576 - extracellular region

Credits:
Created 28-Mar-2011 by Caspi R , SRI International


Enzymatic reaction of: cellulase

EC Number: 3.2.1.4

cellulose + n H2O <=> n a cellodextrin

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

The reaction is physiologically favored in the direction shown.


Subunit of: fully loaded scaffoldin (cellobiose, medium abundance catalytic subunits)

Species: Ruminiclostridium thermocellum ATCC 27405

Subunit composition of fully loaded scaffoldin (cellobiose, medium abundance catalytic subunits) = [CipA][CelB][Cthe_2193][XynD][CelG][CelR][CelF][CbhA][Cthe_0405][Cthe_1271]
         CipA scaffoldin = CipA (extended summary available)
         cellulase B = CelB (extended summary available)
         glycosyl hydrolase family 5 domain protein = Cthe_2193 (summary available)
         endo-1,4-β-xylanase XynD = XynD (extended summary available)
         cellulase G = CelG (extended summary available)
         cellulase R = CelR (summary available)
         cellulase F = CelF (extended summary available)
         cellulose 1,4-β-cellobiosidase CbhA = CbhA (extended summary available)
         glycosyl hydrolase family 5 domain protein = Cthe_0405 (summary available)
         glycosyl hydrolase family 43 domain protein = Cthe_1271 (summary available)

Component of: cellulosome complex (or2p anchor, 18 most abundant catalytic units in cellobiose-grown cells) (extended summary available)

Summary:
This protein complex stands for a CipA scaffoldin protein loaded with nine of the medium abundance catalytic cellulosomal proteins that are expressed in cells of Ruminiclostridium thermocellum grown on β-D-cellobiose (ratio of 1.7-4.2 mol catalyti unit per CipA molecule) [Gold07].

Credits:
Created 04-Apr-2011 by Caspi R , SRI International


Subunit of: cellulosome complex (or2p anchor, 18 most abundant catalytic units in cellobiose-grown cells)

Species: Ruminiclostridium thermocellum ATCC 27405

Subunit composition of cellulosome complex (or2p anchor, 18 most abundant catalytic units in cellobiose-grown cells) = [Orf2p][(Cthe_0032)(CelE)(CelK)(Cthe_0821)(XghA)(CelA)(XynC)(XynA)(XynZ)(CipA)][(CipA)(CelB)(Cthe_2193)(XynD)(CelG)(CelR)(CelF)(CbhA)(Cthe_0405)(Cthe_1271)]
         anchoring scaffoldin Orf2p = Orf2p (extended summary available)
         fully loaded scaffoldin (cellobiose, high abundance catalytic units) = (Cthe_0032)(CelE)(CelK)(Cthe_0821)(XghA)(CelA)(XynC)(XynA)(XynZ)(CipA) (summary available)
                 glycosyl hydrolase family 26 domain protein = Cthe_0032 (summary available)
                 cellulase E = CelE (extended summary available)
                 cellulose 1,4-β-cellobiosidase (non-reducing end) = CelK (extended summary available)
                 glycosyl hydrolase family 5 domain protein = Cthe_0821 (summary available)
                 endo-β-1,4-glucanase XghA = XghA (extended summary available)
                 cellulase A = CelA (extended summary available)
                 endo-1,4-β-xylanase XynC = XynC (extended summary available)
                 endo-1,4-β-xylanase XynA = XynA (extended summary available)
                 endo-1,4-β-xylanase XynZ = XynZ (extended summary available)
                 CipA scaffoldin = CipA (extended summary available)
         fully loaded scaffoldin (cellobiose, medium abundance catalytic subunits) = (CipA)(CelB)(Cthe_2193)(XynD)(CelG)(CelR)(CelF)(CbhA)(Cthe_0405)(Cthe_1271) (summary available)
                 CipA scaffoldin = CipA (extended summary available)
                 cellulase B = CelB (extended summary available)
                 glycosyl hydrolase family 5 domain protein = Cthe_2193 (summary available)
                 endo-1,4-β-xylanase XynD = XynD (extended summary available)
                 cellulase G = CelG (extended summary available)
                 cellulase R = CelR (summary available)
                 cellulase F = CelF (extended summary available)
                 cellulose 1,4-β-cellobiosidase CbhA = CbhA (extended summary available)
                 glycosyl hydrolase family 5 domain protein = Cthe_0405 (summary available)
                 glycosyl hydrolase family 43 domain protein = Cthe_1271 (summary available)

Summary:
The strictly anerobic, thermophilic bacterium Ruminiclostridium thermocellum is the microorganism with the fastest growth rate on the recalcitrant substrate crystalline cellulose [Lynd02]. The higher efficiency of its extracellular hydrolytic machinery over that of other microorganisms is due to the formation of a huge enzyme complex, the cellulosome, which has a size of 18 nm diameter and a mass in excess of 2000 kDa [Shoham99].

The cellulosome is a modular complex. The center of the complex consists of a central non-catalytic protein known as the scaffoldin (CipA), which binds up to nine catalytic subunits [Wu88]. The attachment of each catalytic subunit is mediated by the interaction of its type I dockerin domain with one of the nine type I cohesin domains of CipA [Kruus95a].

CipA is, in turn, bound to the cell surface by the interaction of its type II dockerin domain with the type II cohesin domain of one of three S-layer anchor proteins, SdbA, Orf2p, or OlpB [Bayer98]. Each of these anchor proteins contains a C-terminal S-layer homology module that mediates attachment to the bacterial cell surface, and a different number of type II cohesin modules capable of binding CipA molecules. Thus different anchoring scaffoldins form cellulosome complexes of differing sizes. The smallest one, anchoring scaffoldin SdbA, contains one cohesin domain, and thus binds one CipA molecule along with the nine catalytic units bound to it. The medium size anchoring scaffoldin Orf2p contains two cohesin domains and thus binds two CipA molecules and forms complexes with 18 catalytic units. The most abundant anchor protein is anchoring scaffoldin OlpB, which contains seven cohesin domains and forms complexes of up to 63 catalytic units.

In addition to nine type I cohesin domains and a type II dockerin domain, the CipA scaffoldin also contains a type III cellulose-binding module for attachment of the complex to cellulose [Gerngross93]. Many of the catalytic units also contain carbohydrate-binding domains with differing specificities.

The specific composition of the cellulosomes depends on growth rate and the nature of substrates available. In a 2007 experiment that identified cellulosome components under conditions of growth on either β-D-cellobiose or avicel [Gold07], the following components were detected (in order of abundance):

Proteins detected in avicel-grown cells:

cellulose 1,4-β-cellobiosidase (non-reducing end), cellulose 1,4-β-cellobiosidase (reducing end), cellulase R, anchoring scaffoldin OlpB, Cthe_0821 glycosyl hydrolase family 5 domain protein, cellulase A, cellulase E, cellulase J, endo-1,4-β-xylanase XynC, endo-1,4-β-xylanase XynZ, cellulose 1,4-β-cellobiosidase CbhA, cellulase T, cellulase G, endo-1,4-β-xylanase XynA, endo-β-1,4-glucanase XghA, cellulase W, cellulase F, Cthe_0736 cellulosomal cohesin-domain protein, Cthe_2193 glycosyl hydrolase family 5 domain protein, licheninase LicB, mannanase A, cellulase Q, Cthe_0032 glycosyl hydrolase family 26 domain protein, cellulase B, anchoring scaffoldin Orf2p, cellulase P, Cthe_2761 glycosyl hydrolase family 9 domain protein, Cthe_0405 glycosyl hydrolase family 5 domain protein, cellulase N, cellulase D, glycoside hydrolase family 9 domain protein LecB, endochitinase ChiA, Cthe_1400 glycosyl hydrolase 53 domain protein, pectin lyase.

The following proteins were detected only in avicel-grown cells:

Cthe_0736 cellulosomal cohesin-domain protein, licheninase LicB, mannanase A, cellulase Q, cellulase P, cellulase N, and pectin lyase.

Proteins detected in cellobiose-grown cells:

endo-1,4-β-xylanase XynZ, CipA scaffoldin, endo-1,4-β-xylanase XynA, endo-1,4-β-xylanase XynC, cellulase A, endo-β-1,4-glucanase XghA, Cthe_0821 glycosyl hydrolase family 5 domain protein, cellulose 1,4-β-cellobiosidase (non-reducing end), cellulase E, Cthe_0032 glycosyl hydrolase family 26 domain protein, cellulase B, anchoring scaffoldin OlpB, Cthe_2193 glycosyl hydrolase family 5 domain protein, endo-1,4-β-xylanase XynD, cellulase G, cellulase R, cellulase F, cellulose 1,4-β-cellobiosidase CbhA, Cthe_0405 glycosyl hydrolase family 5 domain protein, Cthe_1271 glycosyl hydrolase family 43 domain protein, Cthe_2761 glycosyl hydrolase family 9 domain protein, cellulase T, cellulase W, cellulose 1,4-β-cellobiosidase (reducing end), endochitinase ChiA, cellulase J, Cthe_1400 glycosyl hydrolase 53 domain protein, glycoside hydrolase family 9 domain protein LecB, α-L-arabinofuranosidase B, anchoring scaffoldin Orf2p, cellulase D, anchoring scaffoldin SdbA, α-L-arabinofuranosidase B, endo-1,4-β-xylanase XynY.

The following proteins were detected only in β-D-cellobiose-grown cells:

endo-1,4-β-xylanase XynD, Cthe_1271 glycosyl hydrolase family 43 domain protein, α-L-arabinofuranosidase B, anchoring scaffoldin SdbA, α-L-arabinofuranosidase B and endo-1,4-β-xylanase XynY

Credits:
Created 04-Apr-2011 by Caspi R , SRI International


References

Bayer98: Bayer EA, Shimon LJ, Shoham Y, Lamed R (1998). "Cellulosomes-structure and ultrastructure." J Struct Biol 124(2-3);221-34. PMID: 10049808

Gerngross93: Gerngross UT, Romaniec MP, Kobayashi T, Huskisson NS, Demain AL (1993). "Sequencing of a Clostridium thermocellum gene (cipA) encoding the cellulosomal SL-protein reveals an unusual degree of internal homology." Mol Microbiol 8(2);325-34. PMID: 8316083

Gold07: Gold ND, Martin VJ (2007). "Global view of the Clostridium thermocellum cellulosome revealed by quantitative proteomic analysis." J Bacteriol 189(19);6787-95. PMID: 17644599

Hazlewood88: Hazlewood, G.P., Romaniec, M.P.M., Davidson, K., Grépinet, O., Béguin, P., Millet, J., Raynaud, O., Aubert, J.P. (1988). "A catalogue of Clostridium thermocellum endoglucanase, β-glucosidase and xylanase genes cloned in Escherichia coli." FEMS Microbiology Letters 51:231-236.

Kruus95a: Kruus K, Lua AC, Demain AL, Wu JH (1995). "The anchorage function of CipA (CelL), a scaffolding protein of the Clostridium thermocellum cellulosome." Proc Natl Acad Sci U S A 92(20);9254-8. PMID: 7568112

Lemaire93: Lemaire M, Beguin P (1993). "Nucleotide sequence of the celG gene of Clostridium thermocellum and characterization of its product, endoglucanase CelG." J Bacteriol 175(11);3353-60. PMID: 8501039

Lynd02: Lynd LR, Weimer PJ, van Zyl WH, Pretorius IS (2002). "Microbial cellulose utilization: fundamentals and biotechnology." Microbiol Mol Biol Rev 66(3);506-77, table of contents. PMID: 12209002

Millet85: Millet, J., Petre, D., Beguin, P., Raynaud, O., Aubert, J. P. (1985). "Cloning of ten distinct DNA fragments of Clostridium thermocellum coding for cellulases (Endoglucanases, cellobiohydrolases, cellulolytic genes)." FEMS Microbiology Letters 29:145-149.

Shoham99: Shoham Y, Lamed R, Bayer EA (1999). "The cellulosome concept as an efficient microbial strategy for the degradation of insoluble polysaccharides." Trends Microbiol 7(7);275-81. PMID: 10390637

Wu88: Wu, J.H.D., Orme-Johnson, W.H., Demain, A.L. (1988). "Two components of an extracellular protein aggregate of Clostridium thermocellum together degrade crystalline cellulose." Biochemistry 27:1703-1709.


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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by SRI International Pathway Tools version 18.5 on Sun Dec 21, 2014, biocyc13.