Construction Of Myosin Model Explaining Difference Between Experimental Results Observed With Scanning Probe And Optical Tweezers

Abstract

Single molecule measurement (SMM) techniques have been applied to myosin. Then, SMMs' results show that, during single ATP hydrolysis cycle, myosins II & V repeat several cycles of association with- and dissociation from an actin filament to generate sliding motion, suggesting that myosin can convert ATP energy by multi-step processes (MSPs). This MSPs cannot be explained by conventional “lever-arm model”, then “Biased Brownian motion (BBM) model” has been proposed for a mechanism of myosin. However, the MSPs have been observed only by SMM with scanning probe (SP), and not observed with optical tweezers (OT) widely used for SMM. Because MSPs have been observed clearly with myosin II & V, it is strongly suggested that BBM is movement mechanism of myosin. Then, why have MSPs not been observed with optical tweezers? In order to answer this question, here, we construct model including characteristics of SP & OT, and simulate movement of myosin attached to measurement probes (SP or OT). Taking into account the effects of measurement probes, we construct 2-dementional potential along an actin filament, and simulate movement of myosin on the 2D potential by Monte Carlo method. For simulation, spring constants of probes parallel and perpendicular to an actin filament are set according to characteristics of each probe. As a result, sliding velocity with SP (∼0.5 um/s) becomes slower than that with OT (∼3 um/s), then MSPs are clearly observed with SP. This result explains well the experimental results with SP and OT.