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April 18, 2007

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Chi Alpha (a Christian Fellowship on campus) recently placed an advertisement (which came word for word from this website) in the Daily Beacon referring to a paper in PNAS and linking it to Intelligent Design. The actual paper makes no such claims.

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

Zev Bryant*, David Altman, and James A. Spudich*,

*Department of Biochemistry, Stanford University School of Medicine, and Department of Physics, Stanford University, Stanford, CA 94305-5307

Contributed by James A. Spudich, November 15, 2006 (received for review October 24, 2006)

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° 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 180° between pre- and poststroke conformations.

Posted by Donna Braquet at April 18, 2007 12:47 PM