Force and kinetics of fast and slow muscle myosin determined with a synthetic sarcomere-like nanomachine

TL;DR

This study uses a synthetic nanomachine to compare the force and kinetics of slow and fast muscle myosin isoforms, revealing their distinct mechanokinetic properties and providing a foundation for future muscle research.

Contribution

It introduces a novel synthetic nanomachine approach to measure and compare the mechanokinetic parameters of slow and fast muscle myosin isoforms.

Findings

Distinct force generation profiles for slow and fast myosin isoforms

Quantitative estimates of motor force and attachment rates

Validation of a stochastic model for myosin ensemble behavior

Abstract

Myosin II is the muscle molecular motor that works in two bipolar arrays in each thick filament of the striated (skeletal and cardiac) muscle, converting the chemical energy into steady force and shortening by cyclic ATP--driven interactions with the nearby actin filaments. Different isoforms of the myosin motor in the skeletal muscles account for the different functional requirements of the slow muscles (primarily responsible for the posture) and fast muscles (responsible for voluntary movements). To clarify the molecular basis of the differences, here the isoform--dependent mechanokinetic parameters underpinning the force of slow and fast muscles are defined with a unidimensional synthetic nanomachine powered by pure myosin isoforms from either slow or fast rabbit skeletal muscle. Data fitting with a stochastic model provides a self--consistent estimate of all the mechanokinetic properties of the motor ensemble including the motor force, the fraction of actin--attached motors and the rate of transition through the attachment--detachment cycle. The achievements in this paper set the stage for any future study on the emergent mechanokinetic properties of an ensemble of myosin molecules either engineered or purified from mutant animal models or human biopsies.