Calcium modulates conformational changes in F-actin induced by smooth muscle heavy meromyosin.
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.
Laboratory of Molecular Mechanisms of Cell Motility, Institute of Cytology, Russian Academy of Sciences, St.-Petersburg.
S V
SV
Avrova
Y S
YS
Borovikov
N N
NN
Efimova
S
S
Chacko
D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000737:chemistry* / Q000378:metabolism; D000205:Actomyosin / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002645:Chickens; D005454:Fluorescence Polarization; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal; D009130:Muscle, Smooth / Q000378:metabolism*; D018994:Myosin Light Chains / Q000378:metabolism; D015879:Myosin Subfragments / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D011487:Protein Conformation; D011817:Rabbits
D000199:Actins; D018994:Myosin Light Chains; D015879:Myosin Subfragments; D000205:Actomyosin; D002118:Calcium