Dimerized Drosophila myosin VIIa: A processive motor

doi:10.1073/pnas.0509935103

Dimerized Drosophila myosin VIIa: A processive motor

*Laboratory of Molecular Physiology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1762;
^‡Department of Biochemistry, Eötvös University, H-1117 Budapest, Pázmány P. sétány 1/C, Hungary; and
^§Developmental, Cell, and Molecular Biology Group, Department of Biology, Duke University, Durham, NC 27708-1000

Edited by Thomas D. Pollard, Yale University, New Haven, CT, and approved February 23, 2006
↵ ^†Y.Y., M.K., and T.S. contributed equally to this work. (received for review November 16, 2005)

Abstract

The molecular mechanism of processive movement of single myosin molecules from classes V and VI along their actin tracks has recently attracted extraordinary attention. Another member of the myosin superfamily, myosin VII, plays vital roles in the sensory function of Drosophila and mammals. We studied the molecular mechanism of Drosophila myosin VIIa, using transient kinetics and single-molecule motility assays. Myosin VIIa moves along actin filaments as a processive, double-headed single molecule when dimerized by the inclusion of a leucine zipper at the C terminus of the coiled-coil domain. Its motility is ≈8–10 times slower than that of myosin V, and its step size is 30 nm, which is consistent with the presence of five IQ motifs in its neck region. The kinetic basis for the processive motility of myosin VIIa is the relative magnitude of the release rate constants of phosphate (fast) and ADP (slow) as in myosins V and VI. The ATPase pathway is rate-limited by a reversible interconversion between two distinct ADP-bound actomyosin states, which results in high steady-state occupancy of a strongly actin-bound myosin species. The distinctive features of myosin VIIa (long run lengths, slow motility) will be very useful in video-based single-molecule applications. In cells, this kinetic behavior would allow myosin VIIa to exert and hold tension on actin filaments and, if dimerized, to function as a processive cargo transporter.

Footnotes

^¶To whom correspondence should be addressed. E-mail: sellersj{at}nhlbi.nih.gov
Author contributions: Y.Y., M.K., T.S., and J.R.S. designed research; Y.Y., M.K., T.S., and F.Z. performed research; Y.Y., M.K., T.S., and D.P.K. contributed new reagents/analytic tools; Y.Y., M.K., T.S., and J.R.S. analyzed data; and Y.Y., M.K., T.S., D.P.K., and J.R.S. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

Abbreviations:

DmVIIa,

Drosophila myosin VIIa;

S1,

subfragment 1;

HMM,

heavy meromyosin;

FIONA,

fluorescence imaging with one-nanometer accuracy.