Mixed-linkage cellooligosaccharides: a new class of glycoside hydrolase inhibitors.
A new class of inhibitors for beta-D-glycoside hydrolases, in which a single alpha-(1-->4)-glycosidic bond is incorporated into an otherwise all-beta-(1-->4)-linked oligosaccharide, is described. Such mixed beta/alpha-linkage cellooligosaccharides are not transition-state mimics, but instead are capable of utilising binding energy from numerous subsites, spanning either side of the catalytic centre, without the need for substrate distortion. This binding is significant; a mixed alpha/beta-D-tetrasaccharide acts competitively on a number of cellulases, displaying inhibition constants in the range of 40-300 microM. Using the Bacillus agaradhaerens enzyme Cel5A as a model system, one such mixed beta/alpha-cellooligosaccharide, methyl 4(II),4(III)-dithio-alpha-cellobiosyl-(1-->4)-beta-cellobioside, displays a K(i) value of 100 microM, an inhibition at least 150 times better than is observed with an equivalent all-beta-linked compound. The three-dimensional structure of B. agaradhaerens Cel5A in complex with methyl 4(II),4(III)-dithio-alpha-cellobiosyl-(1-->4)-beta-cellobioside has been determined at 1.8 A resolution. This confirms the expected mode of binding in which the ligand, with all four pyranosides in the (4)C(1) chair conformation, occupies the -3, -2 and +1 subsites whilst evading the catalytic (-1) subsite. Such "by-pass" compounds offer great scope for the development of a new class of beta-D-glycoside hydrolase inhibitors.
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Centre de Recherches sur les Macromolécules Végétales (CERMAV-CNRS), Affiliated with Université Joseph Fourier, Grenoble B.P. 53, 38041 Grenoble cedex 9, France.
Varrot
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Schülein
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Cottaz
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Driguez
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Davies
G J
GJ
D001407:Bacillus / Q000201:enzymology; D001665:Binding Sites; D002236:Carbohydrate Conformation; D002480:Cellulase / Q000037:antagonists & inhibitors / Q000378:metabolism; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009844:Oligosaccharides / Q000737:chemistry* / Q000378:metabolism
D004791:Enzyme Inhibitors; D009844:Oligosaccharides; D006026:Glycoside Hydrolases; D002480:Cellulase