콘텐츠로 건너뛰기
Merck
  • The power stroke of myosin VI and the basis of reverse directionality.

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

Proceedings of the National Academy of Sciences of the United States of America (2006-12-22)
Zev Bryant, David Altman, James A Spudich
초록

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.