Actine

Actine, commonly called actin in English and actine in several languages, is a highly conserved family of globular proteins that polymerize to form microfilaments, essential components of the eukaryotic cytoskeleton. Actin monomers (G-actin) bind ATP and assemble into filaments (F-actin) that form networks and bundles, supporting cell shape and enabling movement. Actin dynamics are regulated by numerous actin-binding proteins and by cellular signaling.

Actin participates in processes such as maintaining cell shape, generating force for cell migration via lamellipodia and filopodia, and contracting muscles as part of thin filaments with myosin. It also contributes to cytokinesis through the contractile ring and to vesicle transport and organelle positioning.

There are several actin genes encoding isoforms. Cytoplasmic actins include beta-actin (ACTB) and gamma-actin (ACTG1); muscle isoforms include alpha-skeletal actin (ACTA1) and alpha-cardiac actin (ACTC1), among others. The actin family is highly conserved across eukaryotes. Regulation involves profilin, cofilin, Arp2/3, formin, capping proteins such as CapZ and tropomodulin, and tropomyosin, coordinating nucleation, elongation, and stabilization. Abnormal actin function is linked to muscle and cytoskeletal diseases, including myopathies and cardiomyopathies, and to altered cell motility in cancer. Actin is also a common target of toxins and research tools used to study cell biology.