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Calcium modulates conformational changes in F-actin induced by smooth muscle heavy meromyosin
S V Avrova1, Y S Borovikov, N N Efimova
1Laboratory of Molecular Mechanisms of Cell Motility, Institute of Cytology, Russian Academy of Sciences, St.-Petersburg.
Abstract:
The effect of Ca2+ on conformational changes in rhodamine-phalloidin-labeled F-actin induced by binding of smooth muscle heavy meromyosin (HMM) with either phosphorylated or dephosphorylated regulatory light chains (LC20) was studied by polarized fluorimetry. LC20 phosphorylation caused alterations in the F-actin structure typical of the force-producing (strong-binding) state, while dephosphorylation of the chains led to alterations typical of the formation of non-force-producing (weak-binding) state of the actomyosin complex. The presence of Ca2+ enhanced the effect of LC20 phosphorylation and weakened the effect of LC20 dephosphorylation. These data suggest that Ca2+ modulates actin-myosin interaction in smooth muscle by promoting formation of the strong-binding state.