CDNA cloning of human calpastatin: Sequence homology among human, pig, and rabbit calpastatins

cDNA of human calpastatin, an inhibitor protein specific for calpain (EC3.4.22.17; Ca²⁺-dependent cysteine proteinase) was isolated by screening of a library prepared from human liver mRNA with pig calpastatin cDNA fragment as a probe. The primary stnkture of human calpastatin was deduced from the nucleotide sequence of the cDNA and compared with that of pig and rabbit calpastatins already reported. Human calpastatin consisted of 673 amino acid residues and had 78% and 77% indentity to pig or rabbit calpastatins. respectively. Human calpastatin had a domain structure with four internally repetitive sequences and one N-terminal non-homologous sequence like the other calpastatins. Human calpastatin had two deletions, 22 and 13 residues long in domain L and domain 1, respectively, compared to pig or rabbit calpastatins.