Modulation of the mechano-chemical properties of myosin V by drebrin-E.

The regulation of actin filament networks by various proteins has essential roles in the growth cone dynamics. In this study we focused on the actin-myosin interaction which has been suggested to be an important player in the neurite extension. We examined in vitro how the decoration of actin filaments with a side-binding protein, drebrin-E, affects the motile properties of an intracellular transporter myosin V. Single myosin V molecules landed on the drebrin-E-decorated actin filaments with a lower frequency and ran over shorter distances; however, their velocities were normal. Furthermore, the analysis of the movement of myosin V molecules in the optical trap revealed that the decoration of actin filaments with drebrin-E markedly increased the load-sensitivity of the myosin V stepping. These results are attributable to the delay in the attachment of the motor's leading head (ADP·P(i) state) to actin, induced by the competitive binding of drebrin-E to actin, whereas the rate of ADP release from the trailing head (the rate-limiting step in the ATPase cycle of myosin V) is unaffected. Our study indicates that, in addition to the regulation of binding affinity of myosin V, drebrin-E also modulates the chemo-mechanical coupling in the motile myosin V molecules, presumably affecting the movement of the growth cone.