Motors and Forces from a Theoretical Perspective

Forces influence molecular motors on different length scales. At the level of a single motor head, force controls the binding affinity of the associated microfilament or microtubule, an effect that is important for the coordination of conformational changes and enzymatic reactions. On a larger scale, at which motor molecules cooperate either to transport cargos or to generate tension, forces between the motors contribute to the dynamics of such ensembles.We use stochastic descriptions based on finite Markov chains to study motor molecules on these different scales. For single dynein heads we deduce the force-dependent strength of microtubule binding from distributions of unbinding forces measured in optical traps. On the scale of intracellular transport, we extend a stochastic tug-of-war description to explain the bidirectional motility of phagosomes driven by kinesin-1, kinesin-2, and dynein. To understand how forces and nucleotide concentrations regulate the elasticity of a small ensemble of myosin Ic molecules, we introduce a thermodynamically consistent chemomechanical cycle of myosin Ic and integrate it into an ensemble description.
We provide a framework for interpreting experimental findings in order to support or eliminate specific models for the molecular mechanisms.