THE NOVEL LECTIN-LIKE PROTEIN CHB1 IS ENCODED BY A CHITIN-INDUCIBLE STREPTOMYCES-OLIVACEOVIRIDIS GENE AND BINDS SPECIFICALLY TO CRYSTALLINEALPHA-CHITIN OF FUNGI AND OTHER ORGANISMS

The chb1 gene, which encodes the unique lectin-like alpha-chitin-bindi ng protein CHB1 of Streptomyces olivaceoviridis, was cloned. Transform ants of Streptomyces lividans harbouring the plasmid pCHB10 overproduc ed the extracellular CHB1 protein; the protein showed neither enzymati c nor antifungal activity. Biochemical analyses and immunofluorescence microscopy indicated that CHB1 binds strongly to alpha-chitin, but ne ither to chitosan and beta-chitin, nor to various types of cellulose. Within hyphae of fungi, the relative location of crystalline chitin wa s visualized with fluorescein-labelled CHB1. These studies suggest tha t the new protein could serve as a tool to identify alpha-chitin withi n different organisms. The chb1 gene consists of a reading frame of 60 3 bp and its transcription occurred only if the Streptomyces strain wa s cultivated with chitin as the sole carbon source. The deduced mature CHB1 protein (18.7 kDa) shows no apparent similarity to any known pro tein. Within a region containing 100 residues of the deduced CHB1 prot ein, four tryptophan and two asparagine residues as well as one glycin e and one cysteine residue were identified, the relative positions of which are analogous to those of several cellulose-binding domains of b acterial glycohydrolases. The results of spectroscopical studies sugge st a possible involvement of tryptophan residues in the interaction of CHB1 with alpha-chitin.