Primary sequence of the chitosanase from Streptomyces sp. strain N174 and comparison with other endoglycosidases

Abstract

A 1.6-kb DNA fragment from the soil actinomycete, Streptomyces sp. strain N174, containing the gene (csn) encoding an extracellular chitosanase (CSN), has been isolated and its complete nucleotide sequence determined. The gene was expressed in Escherichia coli and Streptomyces lividans using appropriate vectors. The sequence was found to contain one large ORF which encodes a protein of 238 amino acids (aa). The deduced aa sequence begins with a signal peptide which has an unusual C-terminal segment, well recognized by the Streptomyces secretion system, but poorly in Escherichia coli. The strain N174 CSN aa sequence was compared with those of other proteins and significant homology was found only with the Bacillus circulans MH-K1 CSN but not with known chitinases or lysozymes. This suggests that CSN form a new enzyme family distinct from other endoglycosidases.