How Brownian displacement goes down during actin-myosin interaction in the laser trap

Several laboratories have successfully used laser trap technology to observe and score nanometre-size displacements of an actin filament produced by a single myosin molecule. Given the molecular nature of the measurements, the influence of Brownian noise is significant. We use a Langevin-type stochastic model, together with a two-state Huxley kinetics for myosin attachment to and detachment from actin, to describe the magnitude of displacement (fluctuations) for the attached and detached states. When myosin is attached to the actin filament system, we derive an effective (composite) stiffness, which produces a 26% noise reduction compared to the original Brownian noise. With two model mechanisms discussed, the preferred model mechanism predicts a mean myosin-induced actin filament displacement of 8–9 nm, all of which are in very good agreement with recent laser trap experimental observations.