Effect of Nucleotides on the Orientation and Mobility of Myosin Subfragment-1 in Ghost Muscle Fiber

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O. E. Pronina¹, A. Wrzosek², R. Dabrowska², and Yu. S. Borovikov^1*

¹Institute of Cytology, Russian Academy of Sciences, Tikhoretsky pr. 4, 194064 St. Petersburg, Russia; fax: (7-812) 247-0341; E-mail: boroviko@mail.cytspb.rssi.ru

²Nenski Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur Street, Warsaw, 02-093 Poland; fax: (+4822) 8225342

^* To whom correspondence should be addressed.

Received June 30, 2004; Revision received August 18, 2004

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Using polarization fluorimetry, the orientation and mobility of 1,5-IAEDANS specifically bound to Cys707 of myosin subfragment-1 (S1) were studied in ghost muscle tropomyosin-containing fibers in the absence and in the presence of MgADP, MgAMP-PNP, MgATPgammaS, or MgATP. Modeling of various intermediate states was accompanied by discrete changes in actomyosin orientation and mobility of fluorescent dye dipoles. This suggests multistep changes in the structural state of the myosin head during the ATPase cycle. Maximal differences in the probe orientation by 4° and its mobility by 30% were found between actomyosin states in the presence of MgADP and MgATP. It is suggested that interaction of S1 with F-actin induces nucleotide-dependent rotation of the whole motor domain of the myosin head or only the dye-binding site and also change in the head mobility.

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KEY WORDS: muscle contraction, ATP analogs, intermediate states of actomyosin, conformational changes of myosin subfragment-1, fluorescence polarization

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