myosin1

Myosin I, or class I myosin, refers to a family of single-headed, actin-based motor proteins found in eukaryotes. These motors convert chemical energy from ATP hydrolysis into mechanical work, generating force and movement along actin filaments. Unlike dimeric myosins, myosin I typically functions as a monomer and is generally plus-end directed on actin, moving toward the barbed end.

A canonical myosin I molecule comprises three major parts: an N-terminal motor domain that binds actin and hydrolyzes ATP, a neck region containing one or more light chain–binding IQ motifs, and a tail that mediates cargo binding and membrane association. The tail often includes a tail homology 1 (TH1) domain that binds phospholipids, enabling attachment to plasma membranes and vesicles. Some isoforms also harbor additional interaction motifs, such as SH3 domains, which mediate protein–protein interactions.

In animals, several MYO1 genes encode distinct class I myosins, including MYO1A, MYO1B, MYO1C, MYO1D, MYO1E, and MYO1F, among others. The functions of myosin I proteins are diverse and include coupling membranes to the actin cytoskeleton during endocytosis and exocytosis, regulating plasma membrane tension, and driving short-range vesicle or organelle transport. In specialized cells, certain isoforms are linked to mechanosensory processes, such as adaptation in hair cells of the inner ear.

Regulation involves calcium–calmodulin interactions with the light chains and phosphorylation of the regulatory light chain by myosin light chain kinase, which can modulate attachment to actin and motor activity.

Mutations and dysregulation of class I myosins have been associated with human disease in some contexts, including sensory and retinal disorders. Myosin I remains an area of active research for its roles in membrane–cytoskeleton coupling across diverse tissues.