myosine

Myosine is a family of actin-dependent motor proteins that convert chemical energy from ATP hydrolysis into mechanical work. In English literature, the term most often used is myosin; “myosine” is a cognate spelling used in several languages and refers to the same protein family. Myosins interact with actin filaments to generate forces used for muscle contraction and a broad range of cellular processes.

Structure and mechanism: All myosins have a conserved motor domain at the N-terminus that binds actin and hydrolyzes ATP, a neck region with light chains, and a coiled-coil tail for dimerization and cargo binding. Conventional myosin II forms thick filaments in muscle, while unconventional myosins (types I, V, VI, VII, etc.) have diverse tails for membranes or organelles. Most myosins move toward the plus end of actin; myosin VI moves toward the minus end. The catalytic cycle involves ATP binding, detachment, hydrolysis, re-binding, and a power stroke that moves actin or the filament.

Functions: In muscle, myosin II drives contraction; in non-muscle cells, myosins transport vesicles and organelles, regulate membrane tension, and participate in cytokinesis and cell migration.

Genetics and clinical aspects: Myosin genes are numerous, including many MYH (myosin heavy chain) and MYO family members. Mutations in myosin genes are associated with cardiomyopathies such as hypertrophic cardiomyopathy (MYH7) and various myopathies or sensorineural defects depending on isoform. The myosin superfamily is evolutionarily conserved across eukaryotes, reflecting diversification for tissue- and cargo-specific roles.