Granulin-like peptide in the mid-gut gland of the bivalve mollusk, Patinopecten yessoensis.

A cysteine-rich polypeptide, termed CRP1, with a molecular mass of 5829 Da was found to occur in the mid-gut gland of the scallop Patinopecten yessoensis. CRP1 was purified by reverse phase and cation-exchange chromatographies. The amino acid sequence of CRP1 was deduced from its N-terminal amino acid sequence, amino acid composition and the sequence of a partial cDNA, indicating that CRP1 is a 57-amino-acid polypeptide containing 12 cysteine residues with a calculated molecular mass of 5841 Da (5829 Da when oxidized to form six disulfide bridges). A homology search of databases revealed that the deduced amino acid sequence of CRP1 displays significant similarity to those of granulin/epithelins, a family of growth-modulating factors; all cysteine residues in CRP1 are located at the same positions as those conserved characteristically in other known granulin/epithelins. Purified CRP1 inhibited the proliferation of mouse embryo cells. The results suggest that CRP1 functions as a growth-modulating factor in the scallop, and that granulin/epithelin family polypeptides and their precursors play physiologically important roles in invertebrates.