myosineisoformes

Myosine isoformes are the diverse protein variants within the myosin superfamily that act as actin-based molecular motors. They use energy from ATP hydrolysis to generate force and movement, enabling processes from muscle contraction to vesicle transport and organelle positioning. Isoforms can differ in motor characteristics, cargo interactions, regulatory mechanisms, and cellular context.

Myosin genes are organized into several families. The heavy chain genes (MYH) encode the motor domains and coiled-coil tails that determine dimerization and filament assembly, while light chains (such as MYL and Mylk family members) bind near the motor domain to modulate activity and stability. Isoforms can arise through gene duplication, alternative splicing, and tissue-specific promoter usage, producing molecules with distinct kinetic properties, duty cycles, and cargo affinities.

Classically, muscle tissues express myosin II isoforms (for example IIa, IIb, and IIx in mammals) that participate in sarcomere contraction. Non-muscle and membrane-associated myosins (such as types I, V, VI, VII, IX, and others) drive a wide range of cellular tasks, including endocytosis, organelle trafficking, cytokinesis, and cell migration. The tail region of each isoform largely determines motor assembly and cargo binding, while the neck region binds light chains that regulate activity.

Regulation of isoforms occurs through phosphorylation of regulatory light chains, light-chain exchange, and interactions with accessory proteins. Mutations or dysregulation of specific myosin isoforms can contribute to diseases such as cardiomyopathies, deafness, and neuropathies, highlighting their importance in physiology and pathology.