CHARACTERIZATION OF THE EFFECTS OF MUTATION OF THE CALDESMON SEQUENCE(691)GLU-TRP-LEU-THR-LYS-THR(696) TO PRO-GLY-HIS-TYR-ASN-ASN ON CALDESMON-CALMODULIN INTERACTION

We have investigated the functional properties of a mutant (Cg1) deriv ed from the C-terminal 99 amino acids of chicken caldesmon, 658-756 (6 58C) where the sequence (691)glu-trp-leu-thr-lys-thr(696) is changed t o pro-gly-his-tyr-asn-asn. Cg1 bound Ca2+-calmodulin with (In)th of th e affinity as compared to 658C or whole caldesmon. NMR titrations indi cate that the contacts of Ca2+-calmodulin with the Trp-722 region of t he peptide are retained but that those at the mutated site are lost. M ost importantly Ca2+-calmodulin is not able to reverse the Cg1-induced inhibition. We conclude that the interaction of calmodulin with this caldesmon sequence is crucial for the reversal of caldesmon inhibition of actin-tropomyosin activation of myosin ATPase. The results are int erpreted in terms of multisite attachment of actin and Ca2+-calmodulin to overlapping sequences in caldesmon domain 4b. (C) 1998 Federation of European Biochemical Societies.