Human myosin Vc is a low duty ratio nonprocessive motor
Department of Physiology; Program in Molecular Medicine
Medical Subject Headings
Actins; Actomyosin; Adenosine Diphosphate; Adenosine Triphosphatases; Adenosine Triphosphate; Cloning, Molecular; Dose-Response Relationship, Drug; Humans; Kinetics; Microscopy, Fluorescence; Models, Biological; Models, Chemical; Myosin Type V; Protein Isoforms; Time Factors
Life Sciences | Medicine and Health Sciences
There are three distinct members of the myosin V family in vertebrates, and each isoform is involved in different membrane trafficking pathways. Both myosin Va and Vb have demonstrated that they are high duty ratio motors that are consistent with the processive nature of these motors. Here we report that the ATPase cycle mechanism of the single-headed construct of myosin Vc is quite different from those of other vertebrate myosin V isoforms. K(ATPase) of the actin-activated ATPase was 62 microm, which is much higher than that of myosin Va ( approximately 1 mum). The rate of ADP release from actomyosin Vc was 12.7 s(-1), which was 2 times greater than the entire ATPase cycle rate, 6.5 s(-1). P(i) burst size was 0.31, indicating that the equilibrium of the ATP hydrolysis step is shifted to the prehydrolysis form. Our kinetic model, based on all kinetic data we determined in this study, suggests that myosin Vc spends the majority of the ATPase cycle time in the weak actin binding state in contrast to myosin Va and Vb. Consistently, the two-headed myosin Vc construct did not show processive movement in total internal reflection fluorescence microscope analysis, demonstrating that myosin Vc is a nonprocessive motor. Our findings suggest that myosin Vc fulfills its function as a cargo transporter by different mechanisms from other myosin V isoforms.
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Citation: J Biol Chem. 2008 Apr 18;283(16):10581-92. Epub 2007 Dec 12. Link to article on publisher's site
The Journal of biological chemistry
Watanabe, Shinya; Watanabe, Tomonobu M.; Sato, Osamu; Awata, Junya; Homma, Kazuaki; Umeki, Nobuhisa; Higuchi, Hideo; Ikebe, Reiko; and Ikebe, Mitsuo, "Human myosin Vc is a low duty ratio nonprocessive motor" (2007). GSBS Student Publications. 1422.