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Glycoside Hydrolase Family 45
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|Glycoside Hydrolase Family GH45|
|Active site residues||known (but see discussion)|
|CAZy DB link|
Glycoside hydrolases of GH45 are endoglucanases (EC 126.96.36.199); mainly the hydrolysis of soluble β -1,4 glucans. Family 45 enzymes are perhaps best known for their uses in the textile / detergent industries (see for example ).
Kinetics and Mechanism
The enzymes, formally known as cellulase family "K" in some historic literature, act with inversion of anomeric configuration to generate the α-D anomer of the oligosaccaride as product. Based upon the structure of the Humicola insolens endoglucanase V (now known as Cel45) [2, 3] it was concluded that Asp121 (in an HxD motif) acted as the general acid (implied by its hydrogen bonding to the glycosidic oxygen of a ligand in the +1 subsite) and that the most likely general base is Asp10 (in a YxD motif), appropriately positioned "below" the sugar plane. As with many inverting enzymes the base assignment is less secure than that of the acid.
The 3-D structure of canonical GH45 enzymes is a six-stranded β-barrel to which a seventh strand is appended. The structure differs from classical β-barrels in containing both parallel and anti-parallel β-strands. At the time of the first structure solution the fold had ony previously been observed in "Barwin" ; a plant defense protein of unknown function. As is now expected for endo-enzymes, the active centre is located in an open substrate-binding groove. The original native (uncomplexed) structure had an disordered loop above the active centre and this was only seen to become ordered subsequently upon the binding of cello-oligosaccharides .
Family GH45 enzymes are structurally related to plant  and bacterial  expansins. Indeed they even display some of the catalytic centre motifs such as the catalytic acid. The putative catalytic base is absent in plant and bacterial expansins. There are also a few fungal GH45 members, exemplified by Phanerochaete chrysosporium Cel45 which also appear to lack the putative base .
- First sterochemistry determination
- As part of an analysis of many families reported in .
- First general acid/base residue identification
- Catalytic residue proposals have been made solely on the basis of 3-D structure [2, 3].
- First 3-D structure
- The Humicola insolens EGV (now Cel45) by the Davies group .
- Schülein M, Kauppinen M, Lange L, Lassen S, Andersen L, Klysner S, and Nielsen, J (1998) Characterization of fungal cellulases for fiber modification. ACS Symposium Series, 687 (Enzyme Applications in Fiber Processing): 66-74. DOI: 10.1021/bk-1998-0687.ch006
- Davies GJ, Dodson GG, Hubbard RE, Tolley SP, Dauter Z, Wilson KS, Hjort C, Mikkelsen JM, Rasmussen G, and Schülein M. Structure and function of endoglucanase V. Nature. 1993 Sep 23;365(6444):362-4. DOI:10.1038/365362a0 |
- Davies GJ, Tolley SP, Henrissat B, Hjort C, and Schülein M. Structures of oligosaccharide-bound forms of the endoglucanase V from Humicola insolens at 1.9 A resolution. Biochemistry. 1995 Dec 12;34(49):16210-20.
- Ludvigsen S and Poulsen FM. Three-dimensional structure in solution of barwin, a protein from barley seed. Biochemistry. 1992 Sep 22;31(37):8783-9.
- Yennawar NH, Li LC, Dudzinski DM, Tabuchi A, and Cosgrove DJ. Crystal structure and activities of EXPB1 (Zea m 1), a beta-expansin and group-1 pollen allergen from maize. Proc Natl Acad Sci U S A. 2006 Oct 3;103(40):14664-71. DOI:10.1073/pnas.0605979103 |
- Kerff F, Amoroso A, Herman R, Sauvage E, Petrella S, Filée P, Charlier P, Joris B, Tabuchi A, Nikolaidis N, and Cosgrove DJ. Crystal structure and activity of Bacillus subtilis YoaJ (EXLX1), a bacterial expansin that promotes root colonization. Proc Natl Acad Sci U S A. 2008 Nov 4;105(44):16876-81. DOI:10.1073/pnas.0809382105 |
- Igarashi K, Ishida T, Hori C, and Samejima M. Characterization of an endoglucanase belonging to a new subfamily of glycoside hydrolase family 45 of the basidiomycete Phanerochaete chrysosporium. Appl Environ Microbiol. 2008 Sep;74(18):5628-34. DOI:10.1128/AEM.00812-08 |
- Schou C, Rasmussen G, Kaltoft MB, Henrissat B, and Schülein M. Stereochemistry, specificity and kinetics of the hydrolysis of reduced cellodextrins by nine cellulases. Eur J Biochem. 1993 Nov 1;217(3):947-53.