Motor proteins as nanomachines: The roles of thermal fluctuations in generating force and motion. Séminaire Poincaré 2009

Abstract.Motor proteins are enzymes that convert chemical energy derived from the hydrolysis of ATP into mechanical work used to power directed movement along cytoskeletal filaments inside cells. Motor proteins have essential biologi-cal functions such as driving the contraction of muscle, the beating of sperm and cilia, and the transport of intracellular cargoes. Motor proteins are also interesting from a physical point of view because they do what no man-made engines do: they convert or transduce chemical energy directly to mechanical work without using heat or electrical energy as an intermediate. A central issue in the mechanism of this chemomechanical transduction by motor proteins con-cerns the roles played by thermal fluctuations, diffusion and Brownian motion. In this lecture I discuss several molecular models for motor proteins, including so-called ratchet models, and compare predictions of these models to experi-mental results for the microtubule-based motor protein kinesin. I argue that kinesin, which has two motor domains or heads, walks using a hand-over-hand mechanism such that at least one head is bound to the microtubule. Diffusio