Direct Observation of the Myosin Power Stroke and its Reversal

Abstract

Cell locomotion and division, organelle trafficking or signal amplification in hearing are complex forms of cellular motility that require strong coordination of the myosin motors involved. The most basic mechanism of coordination is the direct mechanical interaction of individual myosin motor heads, leading to modification and regulation of their mechano-chemical cycles. We have used an optical tweezers-based assay to study the mechanical response of a single myosin-V motor head to a range of loads. We found this response to be non-linear, including reversibility of the force- generating conformational change (power stroke) of single myosin-V motor heads at intermediate forces. By applying load to the head shortly after binding to actin, we found that at 2-4 pN the power stroke could be reversed and the head fluctuated between an actin-bound pre- and a post-power stroke conformation. Load-dependent mechanical instability might be critical to coordinate the heads of processive, dimeric myosin-V. Non-linear response to load leading to coordination or oscillations amongst motors might be relevant for many cellular functions, including those that involve other members of the myosin superfamily.Supported by MRC, Royal Society, NIH, DFG SFB 863 and Baur-Stiftung.