Characteristics of a Streptomyces coelicolor A3(2) extracellular protein targeting chitin and chitosan

Upstream of the Streptomyces coelicolor A3(2) chitinase G gene, a small gen e (named chb3) is located whose deduced product shares 37% identical amino acids with the previously described CHB1 protein from Streptomyces olivaceo viridis. The chb3 gene and its upstream region were cloned in a multicopy v ector and transformed into the plasmid-free Streptomyces lividans TK21 stra in. The CHB3 protein (14.9 kDa) was secreted by the S. lividans TK21 transf ormant during growth in the presence of glucose, N-acetylglucosamine, yeast extract, and chitin. The protein was purified to homogeneity using anionic exchange, hydrophobic interaction chromatographies, and gel filtration. In contrast to CHB1, CHB3 targets alpha -chitin, beta -chitin, and chitosan a t pH 6.0 but does so relatively loosely. The ecological implications of the divergence of substrate specificity of various types of chitin-binding pro teins are described.