The Group Kinetics of Mechanically Coupled Myosins Show Three Group Size Dependent Regimes

Date

Jun 12, 2013

Time

3:00 PM - 4:00 PM

Speaker

Lennart Hilbert

Affiliation

McGill University, Montréal

Language

en

Main Topic

Physik

Other Topics

Physik

Host

Biological Physics

Description

Background: Groups of protein motors drive cellular cargo transport and contraction. Regarding muscle contraction – which is carried out by the mechanical action of myosin motors on actin filaments – most studies look at single motors, small groups of < 10 motors, or long actin filaments moved by ≥100 motors. Here, we investigated groups of 10-100 mechanically coupled myosin motors. Experimental Methods: To assess the group kinetics at these group sizes, we executed regular in vitro motility assays with purified skeletal muscle myosin: non-filamentous myosin was adhered to a miscroscope cover slip and propelled fluorescently labelled actin filaments across this surface. Actin filaments readily occur at different lengths (L, 0.3 μm1.0μm – continuous sliding. We developed stochastic simulations and a deterministic approximation of the mechano- ehcmical interactions of myosin with myosin-binding sites on an actin filament. In stochastic simulations, mechanical coupling synchronizes myosin working steps into 'cascades', which are separated by phases of 'quiescence'. In a deterministic approximation, we find two stable steady states that correspond to arrest ('quiescence') and sliding ('cascading'). For increasing N, two saddle-node bifurcations occur (only arrest→arrest and sliding coexist→only sliding), corresponding to the experimentally observed L-dependent transitions. Conclusion: Mechanical coupling in groups of myosin motors is currently discussed as an important aspect of muscle molecular mechanics. Our investigation of intermediately-sized groups of skeletal muscle myosin motors revealed the emergence of the macrocopic behavior present at physiologically relevant large group sizes.

Last modified: Jun 12, 2013, 9:55:37 AM