Proteolysis and the domain organization of myosin subfragment 1.

Abstract

Because the proteolytic cleavage of a folded polypeptide depends not only on the specificity of the protease but on the nature of the folding, the cleavage of (chymotryptically produced) subfragment 1 (designated S-1) or head segment of [rabbit skeletal muscle] myosin was investigated by 7 proteases with different specificities. All 7 produced approximately the same 3 fragments of S-1-namely, fragments (from the NH2 terminus) of 27, 50, and 20 kilodaltons, suggesting that in intact S-1 these fragments are distinct domains. The same proteases were used to hydrolyze the MgADP complex of S-1. All failed to do so except trypsin, which makes 2 additional cleavages. This result suggests that the conformational change induced by MgADP opens up only a small stretch of polypeptide chain, which stretch happens to be vulnerable to trypsin.