Proteolytic cleavage sites in smooth muscle myosin‐light‐chain kinase and their relation to structural and regulatory domains

Abstract

Proteolysis of the smooth muscle myosin‐light‐chain kinase with either thermolysin or endoproteinase Lys‐C cleaves the enzyme towards the amino‐terminus between the first and second unc domains, unc‐II‐1 and unc‐II‐2, and in the calmodulin‐binding domain. The thermolytic fragment extends 532 residues from Ser275 to Ala806 and is resistant to further digestion. It is catalytically inactive and does not bind calmodulin. Further proteolysis of the thermolytic fragment with trypsin generates a constitutively active fragment. Digestion with endoproteinase Lys‐C initially results in an inactive fragment of 516 residues, Ala287 to Lys802. Further digestion with Lys‐C endoproteinase results in a con..