Synchronization of elastically coupled processive molecular motors and regulation of cargo transport
06.01.2015
Kohler F, Rohrbach A.
Phys Rev E Stat Nonlin Soft Matter Phys. 2015;91(1-1):012701.
Phys Rev E Stat Nonlin Soft Matter Phys. online article
In biological systems, energetic processes are typically “quantized” by the hydrolysis of adenosine triphosphate (ATP) molecules enabling elementary reactions and conformation changes of proteins. In this way, molecular motors step discontinuously along cytoskeletal filaments in order to transport cargos such as vesicles or to translate filaments for cytoskeletal reorganization. Most motors operate in groups and thereby enable a more efficient cargo transport. However, the observable fingerprints of the quantization, the stepwise movement of the cargo remains hidden.
In other words, measuring the collective work of motor proteins and their inter-motor coupling is difficult as well as comparisons to theoretical predictions, which represents a basic column of understanding in (bio-)physics. We introduce a new observable for motor cooperativity, called "synchronization". This synchronization can be determined from the ratio of the mean times of motor resting and stepping. Results from a multi-state Markov chain model and Brownian Dynamics simulations, describing the elastically coupled motors, coincide well. Our model can explain the experimentally observed effect of strongly increased transport velocities and powers by the synchronization and coupling of myosin V and kinesin I.
In particluar, we have shown that the cargo velocity increases to a maximum with increasing motor synchronization until the cargo stops for full synchronization. The synchronization described here results from the mutual influences of repetitive stochastic molecular processes, which play a significant role for self-organization in many biological systems. Our work enables a comparison between theories and measurements of inter-motor coupling. Thereby it helps to identify motor coupling during cargo transport in fluctuation trajectories measured in both in vivo and in vitro systems.
