Kinetics of myosin subfragment-1-induced condensation of G-actin into oligomers, precursors in the assembly of F-actin-S1. Role of the tightly bound metal ion and ATP hydrolysis.
In a low ionic strength buffer and in the absence of free ATP, the interaction of G-actin (G) with myosin subfragment-1 (S1) leads to the formation of arrowhead-decorated F-actin-S1 filaments, through a series of elementary steps. The initial formation of GS and G2S complexes is followed by their condensation into short oligomers. The kinetics of formation of G-actin-S1 oligomers have been monitored in a stopped-flow apparatus using a combination of light scattering and fluorescence of NBD-labeled actin. Oligomers appear more stable and are formed at a faster rate from MgATP-G-actin than from CaATP-G-actin. The actin-bound ATP is hydrolyzed when oligomers are formed from MgATP-G-actin, not when they are formed from CaATP-G-actin. The formation of oligomers is energetically favored in the presence of cytochalasin D. All data are consistent with the view that the actin-actin interactions which take place upon condensation of GS and G2S into oligomers are very similar to lateral actin-actin interactions along the short pitch helix of actin filaments, which are involved in actin nucleation. These interactions trigger ATP hydrolysis on actin.
Fievez
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Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France.
Pantaloni
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D
Carlier
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MF
D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D015879:Myosin Subfragments / Q000378:metabolism*; D011108:Polymers / Q000378:metabolism; D011817:Rabbits
D000199:Actins; D015879:Myosin Subfragments; D011108:Polymers; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium