MyosinIIKlassen

Myosin II class, also called conventional myosins, is a subfamily of the myosin superfamily. These ATP-dependent motor proteins generate contractile force by moving along actin filaments and play essential roles in both muscle and non-muscle cells. In humans, the class II heavy chains are encoded by MYH9 (myosin IIA), MYH10 (myosin IIB), and MYH14 (myosin IIC).

Each myosin II molecule is a hexamer formed by two heavy chains and two pairs of light chains. The globular motor heads bind actin and hydrolyze ATP, while a long coiled-coil tail mediates dimerization and assembly into bipolar filaments. In non-muscle cells, these bipolar filaments interact with actin networks to generate tension and drive remodeling; in muscle cells, class II myosins contribute to the conventional thick-filament system alongside muscle-specific isoforms.

The human non-muscle class II isoforms are IIA, IIB, and IIC, corresponding to MYH9, MYH10, and MYH14. They are broadly expressed with varying tissue enrichment and can form homo- or heterodimers, contributing to diverse contractile functions in different cell types.

Myosin II converts chemical energy from ATP hydrolysis into mechanical work, enabling processes such as cell migration, cytokinesis, maintenance of cell shape, and vesicle trafficking. Activity is tightly regulated by phosphorylation of the regulatory light chain and, in some contexts, by heavy chain modifications and signaling pathways (for example MLCK and ROCK). Assembly into filaments is also sensitive to ionic strength and phosphorylation state.

Mutations in MYH9 cause MYH9-related disease, a spectrum of platelet and organ abnormalities. Beyond human genetics, myosin II inhibitors (for example blebbistatin) are used to study contractility and cytoskeletal dynamics in cells. The class II myosins remain a focus of research due to their central role in cell mechanics and development.