Significance of the N- and C-terminal regions of CAP-1, a cuticle calcification-associated peptide from the exoskeleton of the crayfish, for calcification

Calcification-associated peptide (CAP)-1 is considered to play an important role in calcification of the exoskeleton of the crayfish, Procambarus clarkii. In this study, in order to clarify the molecular mechanism of calcification, we constructed expression systems of recombinant molecules of CAP-1 and its related peptides in Escherichia coli, and verified the structure–activity relationship of these peptides. The inhibitory assay on calcium carbonate precipitation and the calcium-binding assay showed that the C-terminal acidic region was most important for both activities. The CD spectra of these peptides varied depending on calcium concentration and showed that the N-terminal region is associated with the peptide conformation. These results indicate that the C-terminal part of CAP-1 may concentrate calcium ions for nucleation and/or interact with calcium carbonate precipitate to control the growth and that the N-terminal part contribute to maintaining the peptide conformation.