Rat calpastatin has diverged primary sequence from other mammalian calpastatins but retains functionally important sequences.

Rat calpastatin was cloned for cDNA and sequenced. It comprises 603 amino acid residues and contains four repeats of approx. 140 amino acid residues, each of which has TIPPxYr sequence responsible for calpain-inhibitory activity. However, rat calpastatin has three deletions of 30-40 amino acid residues in the nonessential regions for the inhibitory activity, and consequently, the deduced molecular size is significantly smaller than those of other mammalian calpastatins.