Myosin II Filament Dynamics in Actin Networks Revealed with Interferometric Scattering Microscopy

Lewis S Mosby,Nikolas Hundt,Gavin Young,Adam Fineberg,Marco Polin,Satyajit Mayor,Philipp Kukura,Darius V Köster

doi:10.1016/j.bpj.2020.02.025

Abstract

The plasma membrane and the underlying cytoskeletal cortex constitute active platforms for a variety of cellular processes. Recent work has shown that the remodeling acto-myosin network modifies local membrane organization, but the molecular details are only partly understood because of difficulties with experimentally accessing the relevant time and length scales. Here, we use interferometric scattering microscopy to investigate a minimal acto-myosin network linked to a supported lipid bilayer membrane. Using the magnitude of the interferometric contrast, which is proportional to molecular mass, and fast acquisition rates, we detect and image individual membrane-attached actin filaments diffusing within the acto-myosin network and follow individual myosin II filament dynamics. We quantify myosin II filament dwell times and processivity as functions of ATP concentration, providing experimental evidence for the predicted ensemble behavior of myosin head domains. Our results show how decreasing ATP concentrations lead to both increasing dwell times of individual myosin II filaments and a global change from a remodeling to a contractile state of the acto-myosin network.

Highlights

The dynamics of the cell surface and many cellular processes depend on the interplay between the plasma membrane and the tightly associated dynamic actin cortex [1,2]
We demonstrated that changes in muscle myosin II filament dwell times and myosin filament motion can be reliably tracked within actin networks and that changes in myosin filament dynamics can be related to changes in the acto-myosin network from a remodeling to a contractile state
This is emphasized by the observation that muscle myosin II filaments move longer and more directed in the contractile state than in the remodeling state at 100 mM ATP

Summary

Introduction

The dynamics of the cell surface and many cellular processes depend on the interplay between the plasma membrane and the tightly associated dynamic actin cortex [1,2]. 1946 Biophysical Journal 118, 1946–1957, April 21, 2020 principles controlling the dynamics of such active composites. Despite their relative simplicity, these systems can adopt a range of active states depending on ATP concentration, actin-to-myosin ratio, and actin filament length distribution and concentration [3,4]. Most experimental and theoretical studies of myosin motor properties have relied on experiments with single-motor head domains. To experimentally test the dynamics and properties of multiheaded myosin II filaments, it is necessary to visualize the network components with a subsecond time resolution over timescales of tens of minutes, which has been challenging to achieve with fluorescent probes because of photobleaching and phototoxicity

Methods

Results

Conclusion