actinmotor

Actin motor, or actinmotor, refers to a molecular motor that uses actin filaments as tracks to convert chemical energy from ATP into mechanical work, enabling movement of the motor protein itself or cargo bound to it within cells. The best-known actin motors belong to the myosin superfamily, which includes many classes with diverse roles.

Mechanism and directionality: Myosins move along actin filaments by cycles of ATP binding, hydrolysis, and product release that drive conformational changes in the motor domain. Most myosins move toward the plus end of actin filaments, but certain classes, such as myosin VI, are directed toward the minus end. Step sizes and processivity vary: some myosins, like myosin V, are highly processive and transport cargo over long distances, while skeletal muscle myosin II functions as part of filament ensembles to generate contraction rather than sustained single-molecule movement.

Structure and regulation: Actin motors generally consist of a motor domain that binds ATP and actin, a lever arm that amplifies movements, and a tail or cargo-binding domain that determines specificity. Regulatory light chains and post-translational modifications can modulate activity, binding affinity, and assembly. Tail domains determine localization, cargo interaction, and assembly into larger structures, such as muscle thick filaments for myosin II.

Biological roles and relevance: Actin motors drive muscle contraction, intracellular transport of vesicles and organelles, cell migration, cytokinesis, endocytosis, and organization of actin networks. Disruptions in actin motor function are linked to diseases including certain cardiomyopathies, hearing loss, and developmental disorders. Research uses in vitro motility assays and single-molecule techniques to study their mechanics and regulation.