Investigation Of Multiparticle Motor Protein Dynamics Using Coupled Exclusion Processes

Abstract

We theoretically investigate the interaction of a microfilament and motor proteins within the context of intracellular particle transport. We model the motion of motor proteins on the microfilament as a totally asymmetric simple exclusion process (TASEP). Given that motor proteins occasionally disassociate from the microfilament into the surrounding medium where they propagate by diffusion and whence they may re-associate onto the filament, we model their behavior as a symmetric simple exclusion process (SSEP) and proceed to investigate the consequences of linking the two systems with various couplings (i.e. disassociation and re-association rates). Stationary state properties are found exactly in the limit of strong couplings between the channels. It is shown that strong symmetric couplings between TASEP and SSEP lead to an effective partially asymmetric simple exclusion process (PASEP). However, strong asymmetric couplings yield an effective TASEP with nonzero motor protein flux in the microfilament and zero diffusive flux. Treatment of intermediate couplings yields similar but not exact results. Our calculations show that in all cases there are three stationary phases determined by dynamics at entrances, at exits or in the bulk of the system, while phase boundaries depend on the strength and symmetry of couplings between SSEP and TASEP. Extensive Monte Carlo computer simulations strongly support our theoretical predictions. Theoretical calculations and computer simulations also predict that the symmetry and values of the couplings have a strong influence on motor proteins dynamics. These results suggest that by modifying interactions between motor proteins and microfilaments it is possible to control biological transport processes.