C-Terminus on Acitn: Spectroscopic and Immunochemical Examination of its Role in Actomyosin Interactions
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The understanding of force generation during cyclic interactions of myosin with actin requires a detailed description of actomyosin interface and its evolution during ATP hydrolysis. Until now, driven by the availability of mutants1–4 and atomic resolution structure of actin5, the mapping of actomyosin interface has focused on the determination of myosin binding sites on actin. Two proximal areas on actin, in the N- and C-terminal regions of this protein, have been implicated by structural considerations5,6 and biochemical7,8, immunochemical, NMR, and mutagenic studies1–3,15 in the binding of myosin heads (S-1). Immunochemical10and mutagenic approaches16 suggested also the involvement of residues 91–103 on actin in actomyosin interactions. While the previous studies produced a general agreement on the important contribution of N-terminal acidic residues 1–4 on actin to the activation of the myosin ATPase activity and the motility of actin filaments, the actual role of actin’s C-terminal residues in actomyosin interactions has not been assessed. An interesting approach to this task, which was employed also in the work on LC-2 myosin light chains17, was taken by Labbe et al.10 These authors modified the penultimate cysteine residue on actin, Cys-374, with N-iodoacetyl-N’-(5-sulpho-1-naphtyl)ethylenediamine (1,5- IAEDANS) and showed in solid phase immunochemical assays (ELISA) that S-1 and antidansyl antibodies competed with each other for the binding to the modified cysteine.
KeywordsATPase Activity Myosin Head Myosin ATPase Activity Actin Concentration Myosin Subfragment
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