Myosin V (MyoV) motors have been implicated in the intracellular transport of diverse cargoes including vesicles, organelles, RNA-protein complexes, and regulatory proteins. Here, we have solved the cargo-binding domain (CBD) structures of the three human MyoV paralogs (Va, Vb, and Vc), revealing subtle structural changes that drive functional differentiation and a novel redox mechanism controlling the CBD dimerization process, which is unique for the MyoVc subclass. Moreover, the cargo- and motor-binding sites were structurally assigned, indicating the conservation of residues involved in the recognition of adaptors for peroxisome transport and providing high resolution insights into motor domain inhibition by CBD. These results contribute to understanding the structural requirements for cargo transport, autoinhibition, and regulatory mechanisms in myosin V motors.
The functions of actin and its motor proteins myosins in the cytoplasm have been the subject of research for more than 100 years, but the existence and function of these proteins in the nucleus has been a matter of debate until recently. Recent data has clarified the role of actin and myosin molecules in controlling the dynamics of processes in the cell nucleus, chromatin organization and genome integrity. New microscopy techniques and the use of modified actin-binding probes have made it possible for the first time to directly visualize the polymerization of actin filaments in the nucleus of living cells.
To understand the mechanics and kinetic properties of cytoskeletal molecular motors such as myosin, typically the motor of interest needs to be expressed and purified and then analyzed using a range of in vitro-based assays. In this chapter, we describe how to express and purify myosin using the insect cell system, how to characterize the purified protein by mass photometry and negative-stain EM to assess its quality, and how to perform in vitro assays in which fluorescently labeled myosin walks along actin tracks, including a brief description of adapting these assays for MINFLUX imaging.
Throughout the cell, motor proteins work together to drive numerous molecular processes and functions. For example, ensembles of myosin motors collectively transport vesicles and organelles, maintain membrane homeostasis, and drive muscle contraction. Studying these motors in groups has become increasingly important with work demonstrating the emergence of ensemble behavior distinct from individual motor behavior.
Molecular motors move processively along cytoskeletal filaments by stepping of their motor domains (MDs). Observation of how the MDs step relative to each other reveals the mechanism of motor processivity and various gating mechanisms used by motors to coordinate the catalytic cycles of their MDs. This chapter will discuss developments in simultaneous observation of the stepping motions of the two MDs of processive motors using two-color single-particle tracking microscopy.
An unconventional myosin, myosin VI gene (MYO6), contributes to recessive and dominant hearing loss in humans and mice. The Kumamoto shaker/waltzer (ksv) mouse is a model of deafness resulting from a splice-site mutation in Myo6. While ksv/ksv homozygous mice are deaf due to cochlear hair cell stereocilia fusion at the neonatal stage, the hearing phenotypes of ksv/+ heterozygous mice have been less clear.
