Structural and Functional Analyses of a Strong Chitin-Binding Protein-1 (SCBP-1) from the Exoskeleton of the Crayfish Procambarus clarkii

The organic matrices in the exoskeleton of the crayfish Procambarus clarkii are classified into three groups depending on solubility; acid soluble, acid insoluble-SDS/dithiothreitol (DTT) soluble, and acid insoluble-SDS/DTT insoluble fractions. In our previous studies, Casp-1 and -2 were identified in the acid soluble fraction, and CAP-1 and -2 were identified in the acid insoluble-SDS/DTT soluble fraction. In this study, acid insoluble-SDS/DTT insoluble materials were digested with proteases and the resulting peptides were purified and sequenced. Based on the sequences, a cDNA encoding this protein was cloned. The whole primary sequence of the matrix protein named strong chitin-binding protein-1 (SCBP-1), was deduced. SCBP-1 consisted of 155 amino acid residues and had a Rebers-Riddiford consensus sequence for chitin binding. A recombinant protein of SCBP-N corresponding to the N-terminal part of SCBP-1 showed no chitin-binding ability, while SCBP-C corresponding to the C-terminal part of SCBP-1, showed weak affinity to chitin. These results suggest that the primary sequence of SCBP-1 does not have strong chitin-binding ability. Therefore, SCBP-1 probably binds covalently to chitin through a particular residue contained in the peptide part that was not obtained by protease digestion.