The functional effects of mutations Thr 673 → Asp and Ser 702 → Asp at the Pro-directed kinase phosophorylation sites in the C-terminus of chicken gizzard caldesmon

Abstract

We expressed the C-terminal 99 amino acids of chicken gizzard caldesmon (658C) and two point mutants in which the preferred phosphorylation sites of MAP kinase and p34 cdc2 kinase, Ser 702 and Thr 673 were altered to aspartic acid. The T673D mutant was indistinguishable from 658C but S702D was not phosphorylated by MAP kinase, was significantly less potent as an inhibitor of actin-tropomyosin activation of myosin MgATPase, and bound less actin-tropomyosin at low concentrations. Thus Ser 702 is involved in the tropomyosin-dependent inhibitory mechanism of caldesmon, and its phosphorylation by MAP kinase or p34 cdc2 kinase could modulate caldesmon function.