Contribution of the Myosin VI Tail Domain to Processive Stepping and Intramolecular Tension Sensing

Abstract

Myosin VI is proposed to act as both a molecular transporter and as a cytoskeletal anchor in vivo. The structural traits and kinetic mechanisms by which myosin VI takes processive, ∼36 nm steps along actin are controversial. In particular, the portion of the molecule C-terminal to the canonical lever arm, termed the medial tail (MT), has been hypothesized to act as either a lever arm extension or as a dimerization motif. We created constructs in which the MT is interrupted by glycine-rich molecular swivels in order to test competing models of the MT's contribution to processive stepping. Disruption of the MT results in decreased processive run lengths measured using single-molecule fluorescence microscopy and a decreased step size under applied load as measured in an optical trap (see Figure). We used single-molecule gold nanoparticle tracking and optical trapping to examine the mechanism of coordination between the heads of dimeric myosin VI. We conclude that intramolecular tension prevents ADP release from the lead head. This mechanism likely increases both the motor's processivity and its ability to act as an anchor under physiological conditions.View Large Image | View Hi-Res Image | Download PowerPoint Slide