A MODULAR FAMILY-19 CHITINASE FOUND IN THE PROKARYOTIC ORGANISM STREPTOMYCES-GRISEUS HUT-6037

The specificity of chitinase C-1 of Streptomyces griseus HUT 6037 for the hydrolysis of the beta-1,4-glycosidic linkages in partially acetyl ated chitosan is different from that of other microbial chitinases. In order to study the primary structure of this unique chitinase, the ch iC gene specifying chitinase C-1 was cloned and its nucleotide sequenc e was determined. The gene encodes a polypeptide of 294 amino acids wi th a calculated size of 31.4 kDa. Comparison of the amino acid sequenc e of the deduced polypeptide with that of other proteins revealed a C- terminal catalytic domain displaying considerable sequence similarity to the catalytic domain of plant class I, II, and IV chitinases which form glycosyl hydrolase family 19. The N-terminal domain of the deduce d polypeptide exhibits sequence similarity to substrate-binding domain s of several microbial chitinases and cellulases but not to the chitin -binding domains of plant chitinases. The previously purified chitinas e C-l from S. griseus is suggested to be generated by proteolytic remo val of the N-terminal chitin-binding domain and corresponds to the cat alytic domain of the chitinase encoded by the chiC gene. High-performa nce liquid chromatography analysis of the hydrolysis products from N-a cetyl chitotetraose revealed that chitinase C-l catalyzes hydrolysis o f the glycosidic bond with inversion of the anomeric configuration, in agreement with the previously reported inverting mechanism of plant c lass I chitinases. This is the first report of a family 19 chitinase f ound in an organism other than higher plants.