| Type: | Conserved_site | Name: | Actin/actin-like conserved site |
| Description: | Actin [, ] is a ubiquitous protein involved in the formation of filaments that are major components of the cytoskeleton. These filaments interact with myosin to produce a sliding effect, which is the basis of muscular contraction and many aspects of cell motility, including cytokinesis. Each actin protomer binds one molecule of ATP and has one high affinity site for either calcium or magnesium ions, as well as several low affinity sites. Actin exists as a monomer in low salt concentrations, but filaments form rapidly as salt concentration rises, with the consequent hydrolysis of ATP. Actin from many sources forms a tight complex with deoxyribonuclease (DNase I) although the significance of this is still unknown. The formation of this complex results in the inhibition of DNase I activity, and actin loses its ability to polymerise. It has been shown that an ATPase domain of actin shares similarity with ATPase domains of hexokinase and hsp70proteins [, ].In vertebrates there are three groups of actin isoforms: alpha, beta and gamma. The alpha actins are found in muscle tissues and are a major constituent of the contractile apparatus. The beta and gamma actins co-exists in most cell types as components of the cytoskeleton and as mediators of internal cell motility. In plants there are many isoforms which are probably involved in a variety of functions such as cytoplasmic streaming, cell shape determination, tip growth, graviperception, cell wall deposition, etc.Recently some divergent actin-like proteins have been identified in several species. These proteins include centractin (actin-RPV) from mammals, fungi yeast ACT5, Neurospora crassaro-4) and Pneumocystis carinii, which seems to be a component of a multi-subunit centrosomal complex involved in microtubule based vesicle motility (this subfamily is known as ARP1); ARP2 subfamily, which includes chicken ACTL, Saccharomyces cerevisiaeACT2, Drosophila melanogaster14D and Caenorhabditis elegansactC; ARP3 subfamily, which includes actin 2 from mammals, Drosophila 66B, yeast ACT4 and Schizosaccharomyces pombeact2; and ARP4 subfamily, which includes yeast ACT3 and Drosophila 13E.This entry contains a signature that picks up both actins and the actin-like proteins and corresponds to positions 106 to 118 in actins. | Short Name: | Actin/actin-like_CS |
