Actins
actins
Actins are globular multi-functional proteins that form microfilaments. An actin protein's mass is roughly 42- kDa and they are the monomeric subunit of two types of filaments in cells: microfilaments, one of the three major components of the cytoskeleton, and thin filaments, part of the contractile apparatus in muscle cells. They can be present as either a free monomer called G-actin (globular) or as part of a linear polymer microfilament called F-actin (filamentous) both of which are essential for such important cellular functions as the mobility and contraction of cells during cell division.   Actins participate in many important cellular processes, including muscle contraction, cell motility, cell division and cytokinesis, vesicle and organelle movement, cell signaling, and the establishment and maintenance of cell junctions and cell shape. Many of these processes are mediated by extensive and intimate interactions of actin with cellular membranes. In vertebrates, three main groups of actin isoforms, alpha, beta, and gamma have been identified. The alpha actins, found in muscle tissues, are a major constituent of the contractile apparatus. The beta and gamma actins coexist in most cell types as components of the cytoskeleton, and as mediators of internal cell motility.