MULTI-MOTOR DRIVEN CARGOS: FROM SINGLE MOTOR UNDER LOAD TO THE ROLE OF MOTOR-MOTOR COUPLING

Motor proteins constitute an essential part of the cellular machinery. They have been the subject of intensive experimental and theoretical work in the past two decades, however, their function is far from being understood. In particular, the effect of motor-motor coupling, such as mutual stalling and jamming, when several motors simultaneously carry a single cargo, remains unclear. To examine this, we first construct a simple, yet general, theoretical-phenomenological model for single motor motion. The model correctly predicts the motor step size distribution and its dependence on load, as recently measured in single molecule experiments. We then use our proposed model to predict transport properties of multi-motor complexes, with particular attention to linear cargos with variable flexibility, motor density and number of motors: (i) a chain of motors connected by springs, a recently studied construction for a pair, and (ii) an array of motors all connected by identical springs to a stiff rod, which is essentially a mirror image of standard gliding motility assays. In both systems, and for any number of carrying motors, we find that, while low flexibility results in a strongly damped velocity, increased flexibility renders an almost single motor velocity. Comparing our model based simulations to recent gliding assays we find remarkable qualitative agreement. We also demonstrate consistency with other multi-motor motility assays. We find that, in all cases, the characteristic spring constant, that controls the crossover behavior between high and low velocity regimes, is the stalling force divided by the mean step size. We conjecture that this characteristic spring constant can serve as tool for engineering multi-motor complexes for drug delivery applications.