Skeletal muscle myosin regulatory light chains conformation affects the papain cleavage of A1 light chains

The role of the skeletal muscle myosin light chains N‐terminal fragments

“…However, in the experiments with the rabbit cardiac myosin which had been treated with papain to obtain preparations with the N-terminus of A1 digested off (but with the preserved intact heavy chain) Moczarska and Kgkol [37] observed an increase by one order of magnitude of the myosin affinity to actin. Similar results were obtained by St~pkowski et al [38] for the rabbit fast skeletal muscle myosin, indicating that removal of the N-terminal residues of A1 leads to a strikingly increased affinity of myosin filaments towards actin. Such a behaviour was not observed with the myosin enriched in the shorter isoform of the essential light chain, A2 [20], suggesting that, the Al'-containing preparation is different from the A2 containing preparation.…”

“…Such a behaviour was not observed with the myosin enriched in the shorter isoform of the essential light chain, A2 [20], suggesting that, the Al'-containing preparation is different from the A2 containing preparation. The removal of the N-terminus of A1 in myosin leads to destabilization of the head with time as observed by reduced K ÷ ATPase activity [38]. The destabilization could result from dimerization of heads observed by Margossian et al [36] for the cardiac papain S 1 and by us for the rabbit cardiac and skeletal myosin (unpublished observations).…”

“…The monoclonal antibody binding in a Ca2+-dependent manner to the ELC, demonstrated by Shimizu et al [45] may suggest that light chains undergo conformational changes when one of them (presumably RLC) binds Ca 2+ or Mg 2÷. St~pkowski et al [38] has found, for the rabbit skeletal muscle heavy meromyosin and myosin, that limited proteolysis orAl by papain is dependent both on the cation bound to RLC and the phosphorylation state of RLC. In both cases, those of binding of antibody to A1 or limited proteolysis of the Nterminus of A1, a close direct conformational communication occurs between the two light chains A1 and RLC, involving probably also the heavy chain.…”

“…The N-terminus of A1 is exposed to papain cleavage. The extent of exposition of the N-terminus of A1 for papain cleavage in the presence of actin and ATP was determined from the data described by Stcpkowski et al [38].…”