title: Human myosin Vc is a low duty ratio nonprocessive motor.
abstract: 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.
authors: Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
authors: Shinya
authors: S
authors: Watanabe
authors: Tomonobu M
authors: TM
authors: Watanabe
authors: Osamu
authors: O
authors: Sato
authors: Junya
authors: J
authors: Awata
authors: Kazuaki
authors: K
authors: Homma
authors: Nobuhisa
authors: N
authors: Umeki
authors: Hideo
authors: H
authors: Higuchi
authors: Reiko
authors: R
authors: Ikebe
authors: Mitsuo
authors: M
authors: Ikebe
mesh_terms: D000199:Actins / Q000737:chemistry; D000205:Actomyosin / Q000737:chemistry; D000244:Adenosine Diphosphate / Q000737:chemistry; D000251:Adenosine Triphosphatases / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D003001:Cloning, Molecular; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007700:Kinetics; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D008956:Models, Chemical; D024701:Myosin Type V / Q000737:chemistry* / Q000502:physiology*; D020033:Protein Isoforms; D013997:Time Factors
chemical_list: D000199:Actins; C459104:MYO5C protein, human; D020033:Protein Isoforms; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000205:Actomyosin; D000251:Adenosine Triphosphatases; D024701:Myosin Type V