Light-chain phosphorylation and cross-bridge conformation in myosin from vertebrate skeletal muscle

Abstract

The effect of phosphorylation of the myosin light chains (LC-2) on cross-bridge conformation in synthetic myosin filaments from vertebrate skeletal muscle was studied by using chemical cross-linking and chymotryptic digestion methods. Phosphorylated and dephosphorylated myosin filaments, which were used in these experiments, had similar sedimentation coefficients, turbidities, and rates of growth from the respective minifilament structures. The proteolytic susceptibility at the heavy meromyosin-light meromyosin (HMM-LMM) junction was somewhat greater in the phosphorylated than in the dephosphorylated filaments at both pH 7.0 and pH 8.0. At the same time, the normalized rate of subfragment 2 (S-2) cross-linking to the filament surface, kS-2/kLMM, was reduced by phosphorylation of myosin. These results are consistent with partial release of cross-bridges from the thick filament surface in phosphorylated myosin filaments.

Dynamic Modulation of the Regulatory Domain of Myosin Heads by pH, Ionic Strength, and RLC Phosphorylation in Synthetic Myosin Filaments

“…When S2 is displaced away from the filament surface, the heads gain a larger degree of rotational freedom (EM) as reflected by increased mobility (ST-EPR). Although larger mobility was postulated before (4,6), the current finding is the first direct measurement of such an increase in mobility.…”

“…Phosphorylation of smooth muscle results in the dramatic structural transition between the folded 10S and extended 6S conformations ( − ). In skeletal muscle, the changes are not as dramatic, but still phosphorylation of Ser16 of RLC decreased the efficiency of cross-linking of S2 and the filament surface and promoted proteolysis at the LMM/HMM junction ( , ).…”

Role of magnesium binding to myosin in controlling the state of cross-bridges in skeletal rabbit muscle

“…The binding of Ca2+ to the LC-2 subunits in myosin is unlikely to fulfill such a role in striated skeletal muscle (Mendelson & Cheung, 1976; Sutoh & Harrington, 1977;Cheung & Reisler, 1982). Phosphorylation of the light chains promotes cross-bridge release but does not have a major effect on their disposition (Mrakovcic-Zenic & Reisler, 1983). In contrast to these, the binding of divalent cations to the recently detected low-affinity binding sites located on the myosin rod (Borejdo & Werber, 1982) appears to determine the conformational state of cross-bridges.…”

Variations in cross-bridge attachment rate and tension with phosphorylation of myosin in mammalian skinned skeletal muscle fibers. Implications for twitch potentiation in intact muscle.

“…In addition, it has been shown that the effect of pyrophosphate to dissociate the actomyosin complex is depressed after conversion of myosin to its phosphorylated form, suggesting an increased affinity of phosphorylated myosin for actin (Michnicka et al, 1982). Using synthetic myosin filaments from rabbit skeletal muscle, Mrakovcic and Reisler (1983) found that the rate of cross-linking between myosin subfragment S-2 and light meromyosin was reduced after LC2 phosphorylation. This result was interpreted as evidence that LC2 phosphorylation results in a partial release of cross-bridges away from the thick filament backbone (shown schematically in Fig.…”