Amino acid sequence of squid troponin C

The complete amino acid sequence of squid Todarodes pacificus troponin C (T nC), which was shown to bind only 1 mol Ca2+/mol, was determined by both th e Edman and cDNA methods. The squid TnC is composed of 147 amino acids incl uding an unblocked Pro at the N-terminus and the calculated molecular weigh t is 17003.9. Among the four potential Ca2+-binding sites, namely sites I-I V from the N-terminus, only site IV completely satisfied the consensus amin o acid sequence for the active Ca2+-binding loop. This indicates that squid Ca2+ possesses a single Ca2+-binding site at the site IV as scallop TnCs [ Nishita et al., J. Biol. Chem. 269 (1994) 3464-3468; Ojima et al., Arch. Bi ochem. Biophys. 311 (1994) 272-276). The sequence homology of squid TnC to TnCs of scallop, arthropods, and rabbit was 61%, 31-38%, and 31%, respectiv ely. In the sequence of the central D/E-heilix region of squid and scallop TnCs, a deletion of three amino acids was required to maximize the homology with the other TnCs. (C) 2001 Elsevier Science Inc. All rights reserved.