Interaction of F-actin-AMPPNP with myosin subfragment-1 and troponin-tropomyosin: influence of an extra phosphate at the nucleotide binding site in F-actin on its function.
An unsplitable analogue of ATP (adenylyl imidodiphosphate; AMPPNP) was incorporated into F-actin [Cooke, R. (1975) Biochemistry 14, 3250-3256]. The resulting polymers (F-actin-AMPPNP) activated the ATPase activity of myosin subfragment-1 (S1) as efficiently as normal F-actin; neither the maximum velocity at infinite actin concentration (Vmax) nor the affinity of actin to S1 in the presence of ATP (1/KATPase) changed, which indicates that the terminal phosphate of the bound nucleotide at the cleft region between the two domains of the actin molecule [Kabsch, W., Mannherz, H.G., & Suck, D. (1985) EMBO J. 4, 2113-2118] is not directly involved in a myosin binding site. However, the interaction of F-actin with troponin-tropomyosin was strongly modulated by the replacement of ADP with AMPPNP. The troponin-tropomyosin complex strongly enhanced the activation of S1-ATPase activity by F-actin-AMPPNP in the presence of Ca2+, although it has no effect on the activation by normal F-actin-ADP. KATPase was enhanced about threefold by troponin-tropomyosin in the presence of Ca2+, while Vmax was not markedly changed. F-actin-AMPPNP is highly potentiated by troponin-tropomyosin even with low S1 to actin ratios and at high ATP conditions. In the absence of Ca2+, the activation by F-actin-AMPPNP was inhibited normally by troponin-tropomyosin. The results suggest that the terminal beta-phosphate of the bound nucleotide in F-actin is located in a region which is important for regulation of the interaction with myosin.
Miki
M
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Department of Anatomy, University of Sydney, N.S.W. Australia.
D000199:Actins / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000266:Adenylyl Imidodiphosphate / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D009132:Muscles / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D015879:Myosin Subfragments / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D011817:Rabbits; D014335:Tropomyosin / Q000378:metabolism*; D014336:Troponin / Q000378:metabolism*
D000199:Actins; D015879:Myosin Subfragments; D010710:Phosphates; D014335:Tropomyosin; D014336:Troponin; D000266:Adenylyl Imidodiphosphate; D000251:Adenosine Triphosphatases