Myosin-5 and Myosin-6 Differentially Detect Actin Filament Age

Abstract

Unlike a static and immobile skeleton, the actin cytoskeleton is a highly dynamic network of filamentous actin (F-actin) polymers that continuously turn over. In addition to generating mechanical forces and sensing mechanical deformation, dynamic F-actin networks serve as cellular tracks for myosin motor traffic. Unfortunately, much of our understanding of processive myosins comes from in vitro studies where motility was studied on pre-assembled and artificially stabilized, static F-actin tracks. In this work, we examine the role of actin dynamics in single-molecule myosin motility using assembling F-actin. We chose the two highly processive motors, myosin-5 and myosin-6. On dynamic F-actin, the barbed-end directed myosin-5 is 1.5-fold more processive, whereas its pointed-end directed counterpart myosin-6 is 1.7-fold less processive (both relative to static F-actin). Moreover, while myosin-5 takes longer runs on ADP/Pi-rich (young) portions of the growing filament, myosin-6 takes longer runs along ADP-rich (old) F-actin. These results suggest that actin changes conformation upon Pi release, and that these two myosins respond to this change in opposite ways. Taken together, these experiments define a new mechanism of how myosin traffic may sort on different F-actin networks.