CHITIN-BINDING PROTEIN (CBP21) IN THE CULTURE SUPERNATANT OF SERRATIA-MARCESCENS-2170

A chitin binding protein (CBP21) 21kDa in size, is a major protein in the culture snpernatant when Serratia marcescens 2170 is grown in the presence of chitin, The gene (cbp) for CBP21 was found to be located i n a region 1.5 kb downstream of the chiB gene encoding chitinase B. Th e cbp gene encodes a polypeptide of 197 amino-acids with a calculated size of 21.6 kDa containing a putative signal sequence of 27 amino aci ds. Comparison of the amino acid sequence of the deduced polypeptide w ith that of other proteins showed that CBP21 is similar (45.3% amino a cid identity) to CHB1 of Streptomyces olivaceoviridis. Purified CBP21 prepared from the periplasmic fraction of Escherichia coli carrying th e cloned cbp gene showed its highest binding activity to squid chitin (beta-chitin) followed by colloidal chitin and regenerated chitin. Bin ding of CBP21 to regenerated chitin was affected by pH, in particular, low pH reduced binding activity markedly. The presence of similar chi tin binding proteins in the distantly related microorganisms, Streptom yces and Serratia, suggests a wide distribution of this type of chitin binding protein in chitinolytic microorganisms.