Drosophila myosin VIIA is a high duty ratio motor with a unique kinetic mechanism

UMMS Affiliation

Department of Physiology; Program in Molecular Medicine

Publication Date


Document Type



Actins; Actomyosin; Adenosine Diphosphate; Adenosine Triphosphatases; Adenosine Triphosphate; Animals; Cloning, Molecular; Dimerization; Dose-Response Relationship, Drug; Drosophila; Dynein ATPase; Electrophoresis, Polyacrylamide Gel; Humans; Hydrolysis; Kinetics; Magnesium; Mice; Models, Chemical; Mutation; Myosins; Phosphates; Protein Binding; Protein Isoforms; Time Factors


Life Sciences | Medicine and Health Sciences


Mutations of myosin VIIA cause deafness in various species from human and mice to Zebrafish and Drosophila. We analyzed the kinetic mechanism of the ATPase cycle of Drosophila myosin VIIA by using a single-headed construct with the entire neck domain. The steady-state ATPase activity (0.06 s(-1)) was markedly activated by actin to yield V(max) and K(ATPase) of 1.72 s(-1) and 3.2 microm, respectively. The most intriguing finding is that the ATP hydrolysis predominantly takes place in the actin-bound form (actin-attached hydrolysis) for the actomyosin VIIA ATPase reaction. The ATP hydrolysis rate was much faster for the actin-attached form than the dissociated form, in contrast to other myosins reported so far. Both the ATP hydrolysis step and the phosphate release step were significantly faster than the entire ATPase cycle rate, thus not rate-determining. The rate of ADP dissociation from actomyosin VIIA was 1.86 s(-1), which was comparable with the overall ATPase cycle rate, thus assigned to be a rate-determining step. The results suggest that Drosophila myosin VIIA spends the majority of the ATPase cycle in an actomyosin.ADP form, a strong actin binding state. The duty ratio calculated from our kinetic model was approximately 0.9. Therefore, myosin VIIA is classified to be a high duty ratio motor. The present results suggested that myosin VIIA can be a processive motor to serve cargo trafficking in cells once it forms a dimer structure.

DOI of Published Version



J Biol Chem. 2006 Mar 17;281(11):7151-60. Epub 2006 Jan 16. Link to article on publisher's site

Journal/Book/Conference Title

The Journal of biological chemistry

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PubMed ID