MECHANOCHEMICAL COUPLING OF THE MOTION OF MOLECULAR MOTORS TO ATP HYDROLYSIS

The typical biochemical paradigm for coupling between hydrolysis of AT P and the performance of chemical or mechanical work involves a well-d efined sequence of events (a kinetic mechanism) with a fixed stoichiom etry between the number of ATP molecules hydrolyzed and the turnover o f the output reaction. Recent experiments show, however, that such a d eterministic picture of coupling may not be adequate to explain observ ed behavior of molecular motor proteins in the presence of applied for ces. Here we present a general model in which the binding of ATP and r elease of ADP.serve to modulate the binding energy of a motor protein as it travels along a biopolymer backbone. The mechanism is loosely co upled-the average number of ATPs hydrolyzed to cause a single step fro m one binding site to the next depends strongly on the magnitude of an applied force and on the effective viscous drag force. The statistica l mechanical perspective described here offers insight into how local anisotropy along the ''track'' for a molecular motor, combined with an energy-releasing chemical reaction to provide a source of nonequilibr ium fluctuations, can lead to macroscopic motion.