Interaction of nonpolymerizable actins with myosin.
Polymerization of G-actin in the presence of salt and phalloidin was blocked by treatment of G-actin with m-maleimidobenzoic acid N-hydroxysuccinimide ester (MBS) (designated as m-actin). The actin dimer produced by chemical crosslinking of F-actin with N,N'-p-phenylenedimaleimide did not polymerize and was still dimeric or tetrameric after further treatment with MBS (designated as d-actin). The m- and d-actins retained the ability to bind to myosin heads with apparent dissociation constants of 3-8 x 10(-6) and 3-5 x 10(-7) M, respectively. d-Actin formed a 1:1 actin monomer-myosin head complex. However, m-actin formed a 2:1 m-actin-head complex, suggesting the presence of at least two latent actin-binding sites on a myosin head. ATP weakens only 2- to 6-fold the binding of these complexes. One of two m-actins on a myosin head was replaced by d-actin. Native F-actin blocked the binding of both m- and d-actins to myosin heads in the presence and absence of ATP, although the affinities of myosin head for MBS-treated actins and F-actin are similar in the presence of ATP. These results suggest that there are at least three actin binding sites on a myosin head: one is responsible for binding of F-, m-, and d-actins, the second for binding of F- and m-actins, and the third for binding of F-actin at least in the presence of ATP. F-Actin binding to the third site may in some way block the first and second binding sites.
Arata
T
T
Department of Biology, Faculty of Science, Osaka University.
D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D003432:Cross-Linking Reagents / Q000378:metabolism; D007700:Kinetics; D009132:Muscles / Q000737:chemistry; D009218:Myosins / Q000378:metabolism*; D011487:Protein Conformation; D011817:Rabbits; D013388:Succinimides / Q000378:metabolism*; D014961:X-Ray Diffraction
D000199:Actins; D003432:Cross-Linking Reagents; D013388:Succinimides; C013097:3-maleimidobenzoyl N-hydroxysuccinimide; D000255:Adenosine Triphosphate; D009218:Myosins