Abstract
Characterization of the collective behaviors of different classes of processive motor proteins has become increasingly important to understand various intracellular trafficking and transport processes. This work examines the dynamics of structurally-defined motor complexes containing two myosin Va (myoVa) motors that are linked together via a molecular scaffold formed from a single duplex of DNA. Dynamic changes in the filament-bound configuration of these complexes due to motor binding, stepping, and detachment were monitored by tracking the positions of different color quantum dots that report the position of one head of each myoVa motor on actin. As in studies of multiple kinesins, the run lengths produced by two myosins are only slightly larger than those of single motor molecules. This suggests that internal strain within the complexes, due to asynchronous motor stepping and the resultant stretching of motor linkages, yields net negative cooperative behaviors. In contrast to multiple kinesins, multiple myosin complexes move with appreciably lower velocities than a single-myosin molecule. Although similar trends are predicted by a discrete state stochastic model of collective motor dynamics, these analyses also suggest that multiple myosin velocities and run lengths depend on both the compliance and the effective size of their cargo. Moreover, it is proposed that this unique collective behavior occurs because the large step size and relatively small stalling force of myoVa leads to a high sensitivity of motor stepping rates to strain.
Highlights
Collective myosin Va functions are important to various transport processes in eukaryotes
The dynamic behaviors of motor complexes containing two elastically coupled myosin Va (myoVa) motors were examined using quantum dots (Qdots) motor labeling and tracking procedures that facilitate direct analyses of the relative motions of each motor within a complex as well as the rate that they transition between different motorbound configurations via motor filament binding and detachment. These experiments provide a foundation to parameterize transition rate models of multiple motor dynamics that account for the influence of elastic coupling on cargo transport by multiple motors in the absence of an applied load
The present experimental and theoretical analyses both show that elastic coupling tends to reduce multiple myosin run lengths and velocities
Summary
Collective myosin Va functions are important to various transport processes in eukaryotes. Conclusion: The large step size and small stall force of myosin Va yields a dependence of multiple myosin behaviors on the structural and mechanical properties of cargos. As in studies of multiple kinesins, the run lengths produced by two myosins are only slightly larger than those of single motor molecules. This suggests that internal strain within the complexes, due to asynchronous motor stepping and the resultant stretching of motor linkages, yields net negative cooperative behaviors. Similar trends are predicted by a discrete state stochastic model of collective motor dynamics, these analyses suggest that multiple myosin velocities and run lengths depend on both the compliance and the effective size of their cargo. It is proposed that this unique collective behavior occurs because the large step size and relatively small stalling force of myoVa leads to a high sensitivity of motor stepping rates to strain
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