How these little proteins perform their duties is becoming clearer to scientists using an extremely sensitive measurement technique. Myosin VI, they found, moves by the same "hand-over-hand" mechanism as two other molecular motors, myosin V and kinesin.
"Now that a third molecular motor has been found to move in the same hand-over-hand fashion, the argument for a rival 'inchworm' motion is getting pretty weak," said Paul Selvin, a professor of physics at the University of Illinois at Urbana-Champaign and a co-author of a paper to appear in the Journal of Biological Chemistry.
Myosin VI is a reverse-direction molecular motor that moves materials to various locations within a living cell. Like the related protein myosin V, myosin VI has two "arms" connected to a "body." The tiny molecule converts chemical energy into mechanical motion, and transports its load by "stepping" along polarized filaments of actin -- but in the opposite direction from other myosin variants.
"Studies have suggested two main models for the stepping movement," Selvin said. "One is the hand-over-hand model in which the two arms alternate in the lead. The other model is the inchworm model in which one arm always leads."
To examine the myosin VI stepping mechanism, the researchers applied the same technique that was used to study both myosin V and kinesin. Called FIONA -- Fluorescence Imaging with One Nanometer Accuracy -- the measurement technique can track the position of a single molecule to within 1.5 nanometers. (One nanometer is a billionth of a meter, or about 10,000 times smaller than the width of a human hair).
"First, we attached a small fluorescent dye to one of the arms and took a picture wit
Contact: James E. Kloeppel, Physical Sciences Editor
University of Illinois at Urbana-Champaign