Cloning and expression of a cDNA encoding a matrix peptide associated with calcification in the exoskeleton of the...

Calcification-associated peptide (CAP)-1 isolated from the exoskeleton of the crayfish, Procambarus clarkii, has anti-calcification activity and chitin-binding ability and is, therefore, considered to be associated with calcification. In this study, a cDNA encoding CAP-1 was cloned and characterized. An open reading frame encoded a pre-propeptide of 99 amino acid residues, which was composed of a signal peptide, a CAP-1 precursor and two-basic amino acid residues at the C-terminus. The dibasic residues were not observed in the natural CAP-1. Expression analyses using Northern blot and RT-PCR revealed that the mRNA encoding CAP-1 was strongly expressed in the epidermal tissue during the postmolt stage, where and when the calcification takes place. These results support that CAP-1 may play an important role in the calcification of the exoskeleton. Based on the nucleotide sequence of the cDNA encoding CAP-1, a recombinant CAP-1 and that carrying the basic residues at the C-terminus were expressed in Escherichia coli. Anti-calcification assay showed that these recombinant peptides were less active than natural CAP-1, indicating that the phosphate group at the 70th residue, Ser, in natural CAP-1 is important for inhibitory activity and that the paired basic residues have some contribution to the elevation of inhibitory activity.