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J. Biol. Chem., Vol. 280, Issue 37, 32061-32068, September 16, 2005

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Myosin VIIB from Drosophila Is a High Duty Ratio Motor^*

From the Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892-1762

Myosin VII is an unconventional myosin widely expressed in organisms ranging from amoebae to mammals that has been shown to play vital roles in cell adhesion and phagocytosis. Here we present the first study of the mechanism of action of a myosin VII isoform. We have expressed a truncated single-headed Drosophila myosin VIIB construct in the baculovirus-Sf9 system that bound calmodulin light chains. By using steady-state and transient kinetic methods, we showed that myosin VIIB exhibits a fast release of phosphate and a slower, rate-limiting ADP release from actomyosin. As a result, myosin VIIB will be predominantly strongly bound to actin during steady-state ATP hydrolysis (its duty ratio will be at least 80%). This kinetic pattern is in many respects similar to that of the single-molecule vesicle transporters myosin V and VI. The enzymatic properties of myosin VIIB provide a kinetic basis for processivity upon possible dimerization via the C-terminal domains of the heavy chain. Our experiments also revealed conformational heterogeneity of the actomyosin VIIB complex in the absence of nucleotide.

Received for publication, June 21, 2005 , and in revised form, July 22, 2005.

^* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Both authors contributed equally to this work.

² To whom correspondence should be addressed: Laboratory of Molecular Physiology, NHLBI, Bldg. 10, Rm. 8N202, National Institutes of Health, Bethesda, MD 20892-1762. Tel.: 301-496-6887; Fax: 301-402-1542; E-mail: sellersj{at}nhlbi.nih.gov.

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