Structure of the D140N mutant of chitinase B from Serratia marcescens at 1.45 AÊ resolution

# 2002 International Union of Crystallography Printed in Denmark ± all rights reserved The crystal structure of the inactive D140N mutant of Serratia marcescens was re®ned to 1.45 AÊ resolution. The structure of the mutant was essentially identical to that of the wild type, with the exception of a rotation of Asp142 in the catalytic centre. In the mutant, this residue interacts with the catalytic acid (Glu144) and not with residue 140 as in the wild type. Thus, the 500-fold decrease in activity in the D140N mutant seems to be largely mediated by an effect on Asp142, con®rming the crucial role of the latter residue in catalysis. Received 30 July 2001 Accepted 7 November 2001