The novel lectin‐like protein CHB1 is encoded by a chitin‐inducible Streptomyces olivaceoviridis gene and binds specifically to crystalline α‐chitin of fungi and other organisms

Abstract

The chb1 gene, which encodes the unique lectin-like alpha-chitin-binding protein CHB1 of Streptomyces olivaceoviridis, was cloned. Transformants of Streptomyces lividans harbouring the plasmid pCHB10 overproduced the extracellular CHB1 protein; the protein showed neither enzymatic nor antifungal activity. Biochemical analyses and immunofluorescence microscopy indicated that CHB1 binds strongly to alpha-chitin, but neither to chitosan and beta-chitin, nor to various types of cellulose. Within hyphae of fungi, the relative location of crystalline chitin was visualized with fluorescein-labelled CHB1. These studies suggest that the new protein could serve as a tool to identify alpha-chitin within different organisms. The chb1 gene consists of a reading frame of 603 bp and its transcription occurred only if the Streptomyces strain was cultivated with chitin as the sole carbon source. The deduced mature CHB1 protein (18.7 kDa) shows no apparent similarity to any known protein. Within a region containing 100 residues of the deduced CHB1 protein, four tryptophan and two asparagine residues as well as one glycine and one cysteine residue were identified, the relative positions of which are analogous to those of several cellulose-binding domains of bacterial glycohydrolases. The results of spectroscopical studies suggest a possible involvement of tryptophan residues in the interaction of CHB1 with alpha-chitin.

Multiple genes involved in chitin degradation from the marine bacterium Pseudoalteromonas sp. strain S91

“…The gene encoding this 53 kDa chitinbinding protein has not yet been identified. These data are consistent with those found for Streptomyces olivaceoviridis, in which a 20 kDa extracellular chitinbinding protein (CHB1) lacking chitinolytic activity has been identified (Schnellmann et al, 1994). It was suggested that the function of CHBl is to assist chitinase enzymes in hydrolytic digestion of bound chitin.…”

The Non-catalytic Chitin-binding Protein CBP21 from Serratia marcescens Is Essential for Chitin Degradation

“…While chitinases such as ChiA, ChiB, and ChiC also contain auxiliary CBMs, most microorganisms containing chitinase genes also contain a gene encoding for a homologue of CBP21, that is, a non-catalytic chitin-binding protein. Although these proteins have been hypothesized to assist chitinases in chitin degradation, possibly by disrupting chitin (25), this has so far not been shown experimentally.…”

“…It should be noted that there are homologues of CBP21 (e.g. CHB1 from Streptomyces olivaoceviridis, which is 46% identical in sequence) that bind strictly to ␣-chitin (25).…”

“…This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. clear, but it has been hypothesized that they may play a role in microbial attachment to chitin or to enhance substrate availability by disruption of crystalline chitin (25). Auxiliary CBMs in cellulases (34 -37) and amylases (38) have also been suggested to work at least in part by disrupting substrate structure, but experimental evidence in support of this hypothesis is scarce.…”

“…Homologues of the cbp21 gene can be found in the genomes of most microorganisms which possess chitinase genes. Chitin binding has been demonstrated for a few of these homologues (21,(23)(24)(25)(26), including a study showing that binding is not limited to the surface, but also involves intrusion into the chitin structure (27). Homologues also occur in insect viruses (named GP37 or fusolin proteins in baculoviruses and entomopoxviruses, respectively; see Ref.…”