Cloning and sequence of a cDNA encoding Akazara scallop troponin C

A cDNA clone encoding troponin C of Akazara scallop (Chlamys nipponensis akazara) striated adductor muscle was isolated and sequenced. The cDNA is composed of 1987 bp and has an open reading frame of 462 bp at nucleotide positions 12-473. The amino acid sequence deduced from the cDNA showed 89% homology with that of Ezo-giant scallop (Patinopecten yessoensis) troponin C (K. Nishita, H. Tanaka, and T. Ojima, 1994, J. Biol. Chem. 269, 3464-3468). However, it showed lower homology with those of troponin Cs from the other invertebrates (35-40%) and vertebrates (30%). A single functional Ca(2+)-binding site was found in site IV of the four potential Ca(2+)-binding sites as in the case of Ezo-giant scallop troponin C. Three amino acid deletions in the central D/E helix were required to align the scallop sequences with those of other troponin Cs.