Miozin

Miozin, commonly known as myosin in English, is a family of ATP-powered motor proteins that convert chemical energy into mechanical work by moving along actin filaments. They play essential roles in muscle contraction as well as in diverse cellular processes such as vesicle transport, cytokinesis, and cell shape changes.

Structurally, a typical miozin molecule consists of a motor domain at the head that binds actin and hydrolyzes ATP, a flexible neck region that binds light chains, and a long coiled-coil tail that drives dimerization and determines cargo binding or filament organization. Different miozin classes have distinct tail regions that target them to specific cellular locations or roles.

In skeletal and cardiac muscle, myosin II forms thick fila­ments. The myosin heads cyclically interact with actin filaments to generate a power stroke that slides the thick and thin filaments past one another, producing contraction. This contraction is regulated by calcium via the troponin–tropomyosin complex on actin filaments. In non-muscle cells, other myosins (such as I, V, and VI) function in cargo transport, membrane trafficking, signal transduction, and maintenance of cell architecture.

The motor activity of miozins relies on a cyclical mechanism: ATP binding causes dissociation from actin, ATP hydrolysis primes the head, and release of products leads to force-generating conformational changes that move the actin filament by small increments. Regulation of miozin activity occurs through phosphorylation of light chains in some classes and, in muscle, through calcium-dependent control of actin accessibility.

Miozin represents a diverse superfamily of conserved ATPases found in eukaryotes, central to cellular force generation and movement.