Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 103, Issue 15, Pages 5746-5751Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0509935103
Keywords
fluorescence imaging with one-nanometer accuracy; kinetics; processivity
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Funding
- FIC NIH HHS [1 R01 TW007241-01, R01 TW007241, R01 TW006230, D43 TW006230] Funding Source: Medline
- NIDCD NIH HHS [R01 DC007673] Funding Source: Medline
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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 Vila, using transient kinetics and single-molecule motility assays. Myosin Vila 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 approximate to 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 Vila 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 Vila (long run lengths, slow motility) will be very useful in video-based single-molecule applications. in cells, this kinetic behavior would allow myosin Vila to exert and hold tension on actin filaments and, if dimerized, to function as a processive cargo transporter.
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