Cooperative rigor binding of myosin to actin is a function of F-actin structure.
Many aspects of cooperative behavior within pure F-actin filaments have now been described. We have used two myosin fragments, heavy meromyosin (HMM) and Subfragment 1 (S1), to look at the rigor binding to different forms of F-actin. With Ca2+ bound at the high-affinity metal binding site in actin, there is a very large cooperativity in the binding of HMM, but no cooperativity for S1. With Mg2+ bound at the high affinity site, or with conditions that stabilize the conformation of subdomain-2 of actin, there is no cooperativity seen with either HMM or S1. These results show that the two heads of HMM can induce structural changes in F-actin that are not observed with the single head of S1. They also support the notion that the binding of myosin to F-actin induces a conformational change in subdomain-2 of actin, and that under certain conditions this conformational change can be cooperatively propagated through an actin filament.
Orlova
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A
Dept. of Cell Biology and Neuroanatomy, University of Minnesota Medical School, Minneapolis 55455, USA.
Egelman
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EH
D000199:Actins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure*; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism; D008854:Microscopy, Electron; D015394:Molecular Structure; D015879:Myosin Subfragments / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D009218:Myosins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure*; D011485:Protein Binding; D011487:Protein Conformation; D011817:Rabbits
D000199:Actins; D015879:Myosin Subfragments; D009218:Myosins; D008274:Magnesium; D002118:Calcium