Trp122 and Trp134 on the surface of the catalytic domain are essential for crystalline chitin hydrolysis by Bacillus circulans chitinase A1

From the 3D-structural analysis of the catalytic domain of chitinase Al, two exposed tryptophan residues (W122 and W134) are proposed to play an important role in guiding a chitin chain into the catalytic cleft during the crystalline chitin hydrolysis, Mutation of either W122 or W134 to alanine significantly reduced the hydrolyzing activity against highly crystalline B-chitin microfibrils, Double mutation almost completely abolished the hydrolyzing activity, On the other hand, the hydrolyzing activity against either soluble or amorphous substrate was not reduced. These mutations slightly impaired the binding activity of this enzyme. These results clearly demonstrated that the two exposed aromatic residues play a critical role in hydrolyzing the chitin chain in crystalline chitin. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B,V, All rights reserved.