PHOSPHORYLATION OF CALMODULIN BY MYOSIN LIGHT-CHAIN KINASE IS ALTEREDBY EXCHANGE OR DUPLICATION OF EF-HAND PAIRS

We have previously demonstrated that under certain conditions, myosin light chain kinase can phosphorylate its activator, calmodulin. In thi s study we show that myosin light chain kinase from chicken gizzard ca n phosphorylate recombinant calmodulins in which the EF-hand pairs (Ca 2+-binding domains) are duplicated or exchanged, Three mutants were us ed CaMNN (the amino-terminal EF-hand pair is duplicated), CaMCC (the c arboxy-terminal EF-hand pair is duplicated) and CaMCN (the carboxy- an d amino-terminal EF-hand pairs are switched), Myosin light chain kinas e phosphorylated CaMNN and CaMCN to a greater extent than wild-type Ca M but did not phosphorylate CaMCC. While CaMCC is a competitive inhibi tor of myosin light chain kinase-catalyzed phosphorylation of myosin l ight chains, it did not prevent the phosphorylation of native calmodul in under the conditions employed in these studies, These data suggest that, although the carboxy- and amino-terminal EF-hand pairs are simil ar, their orientation can be distinguished by chicken gizzard myosin l ight chain kinase. (C) 1997 Academic Press.