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CELLOBIOHYDROLASE II (CEL6A) FROM HUMICOLA INSOLENS
Structural highlights
FunctionGUX6_HUMIN Plays a central role in the recycling of plant biomass. The biological conversion of cellulose to glucose generally requires three types of hydrolytic enzymes: (1) Endoglucanases which cut internal beta-1,4-glucosidic bonds; (2) Exocellobiohydrolases that cut the dissaccharide cellobiose from the non-reducing end of the cellulose polymer chain; (3) Beta-1,4-glucosidases which hydrolyze the cellobiose and other short cello-oligosaccharides to glucose.[1] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe three-dimensional structure of the catalytic core of the family 6 cellobiohydrolase II, Cel6A (CBH II), from Humicola insolens has been determined by X-ray crystallography at a resolution of 1.92 A. The structure was solved by molecular replacement using the homologous Trichoderma reesei CBH II as a search model. The H. insolens enzyme displays a high degree of structural similarity with its T. reesei equivalent. The structure features both O- (alpha-linked mannose) and N-linked glycosylation and a hexa-co-ordinate Mg2+ ion. The active-site residues are located within the enclosed tunnel that is typical for cellobiohydrolase enzymes and which may permit a processive hydrolysis of the cellulose substrate. The close structural similarity between the two enzymes implies that kinetics and chain-end specificity experiments performed on the H. insolens enzyme are likely to be applicable to the homologous T. reesei enzyme. These cast doubt on the description of cellobiohydrolases as exo-enzymes since they demonstrated that Cel6A (CBH II) shows no requirement for non-reducing chain-ends, as had been presumed. There is no crystallographic evidence in the present structure to support a mechanism involving loop opening, yet preliminary modelling experiments suggest that the active-site tunnel of Cel6A (CBH II) is too narrow to permit entry of a fluorescenyl-derivatized substrate, known to be a viable substrate for this enzyme. Crystal structure of the catalytic core domain of the family 6 cellobiohydrolase II, Cel6A, from Humicola insolens, at 1.92 A resolution.,Varrot A, Hastrup S, Schulein M, Davies GJ Biochem J. 1999 Jan 15;337 ( Pt 2):297-304. PMID:9882628[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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