aktina

Actin, known as aktina in some languages, is a highly conserved, abundant protein that forms microfilaments, the principal component of the cytoskeleton in eukaryotic cells. It exists in several isoforms, including alpha-actins in muscle tissue and beta- and gamma-actins in non-muscle cells. Actin monomers (G-actin) polymerize into filamentous filaments (F-actin) in a process that is ATP-dependent and polar, with a fast-growing barbed (+) end and a slower pointed (-) end.

Nucleation of actin filaments is facilitated by proteins such as formins and the Arp2/3 complex; elongation is aided by profilin, while capping proteins regulate filament length and turnover. Severing proteins like cofilin promote filament disassembly, allowing rapid rearrangement of the cytoskeleton to meet cellular needs. The dynamic remodeling of actin networks underpins many cellular processes.

Actin plays a central role in maintaining cell shape and mechanical integrity, establishing polarity, and generating force for cell movement and adhesion. It is essential for cytokinesis during cell division and for intracellular transport and organelle positioning. In muscle cells, actin filaments interact with myosin to produce contraction, forming the contractile apparatus of muscle fibers.

Nuclear actin has roles in transcription, chromatin remodeling, and chromatin-associated processes, though these functions are less well understood than cytoplasmic roles. The actin gene family includes several loci (for example ACTA, ACTB, ACTC, ACTG), and mutations can cause a range of myopathies and cardiomyopathies. Actin’s ubiquity and versatility make it fundamental to cell biology and human health.