The power stroke of myosin VI and the basis of reverse directionality.

Abstract

Myosin VI supports movement toward the (-) end of actin filaments, despite sharing extensive sequence and structural homology with (+)-end-directed myosins. A class-specific stretch of amino acids inserted between the converter domain and the lever arm was proposed to provide the structural basis of directionality reversal. Indeed, the unique insert mediates a 120 degrees redirection of the lever arm in a crystal structure of the presumed poststroke conformation of myosin VI [Ménétrey J, Bahloul A, Wells AL, Yengo CM, Morris CA, Sweeney HL, Houdusse A (2005) Nature 435:779-785]. However, this redirection alone is insufficient to account for the large (-)-end-directed stroke of a monomeric myosin VI construct. The underlying motion of the myosin VI converter domain must therefore differ substantially from the power stroke of (+)-end-directed myosins. To experimentally map out the motion of the converter domain and lever arm, we have generated a series of truncated myosin VI constructs and characterized the size and direction of the power stroke for each construct using dual-labeled gliding filament assays and optical trapping. Motors truncated near the end of the converter domain generate (+)-end-directed motion, whereas longer constructs move toward the (-) end. Our results directly demonstrate that the unique insert is required for directionality reversal, ruling out a large class of models in which the converter domain moves toward the (-) end. We suggest that the lever arm rotates approximately 180 degrees between pre- and poststroke conformations.

• Authors: Zev Bryant, David Altman, James A Spudich
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 104 Issue 3 Pg. 772-7 (Jan 16 2007) ISSN: 0027-8424 [Print] United States
• PMID: 17182734 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Actins
• myosin VI
• Myosin Heavy Chains

Topics

• Actins (chemistry, metabolism)
• Amino Acid Sequence
• Animals
• Kinetics
• Models, Molecular
• Molecular Sequence Data
• Movement
• Myosin Heavy Chains (chemistry, genetics, metabolism)
• Protein Structure, Tertiary
• Sequence Alignment
• Swine