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Ras homolog gene family, member A (RhoA) is a small GTPase protein of Rho family. While the effects of RhoA activity are not all well known, it is primarily associated with cytoskeleton regulation, mostly actin stress fibers formation and actomyosin contractility. In humans, it is encoded by the gene ''RHOA''. It acts upon several effectors. Among them, ROCK1 (Rho-associated, coiled-coil containing protein kinase 1) and DIAPH1 (Diaphanous Homologue 1, a.k.a hDia1, homologue to mDia1 in mouse, diaphanous in ''Drosophila'') are the best described. RhoA, and the other Rho GTPases, are part of a larger family of related proteins known as the Ras superfamily, a family of proteins involved in the regulation and timing of cell division. RhoA specifically is regarded as a prominent regulatory factor in other functions such as the regulation of cytoskeletal dynamics, transcription, cell cycle progression and cell transformation. == Structure == Similar to other GTPases, RhoA contains both inactive GDP-bound and active GTP-bound states; these states alternate between the active and inactive states via the exchange of GDP to GTP (conducted simultaneously via guanine nucleotide exchange factors and GTPase activating factor). RhoA contains four insertion or deletion sites with an extra helical subdomain; these sites are characteristic of many GTPases in the Rho family. The GDP- and GTP-bound structural states can be distinguished based on their switch I and switch II conformations; both of these switches have characteristic folding and correspond to specific regions on the RhoA coil and are uniformly stabilized via hydrogen bonds. RhoA is activated primarily by guanine nucleotide exchange factors (GEFs) via phosphorylation; due to large network of overlapping phosphorylation, a multitude of GEFs are utilized to enable specific signaling pathways. These structural arrangements provide interaction sites that can interact with effectors and guanine factors in order to stabilize and signal the hydrolysis of GTP. The primary protein sequences of members of the Rho family are mostly identical, with the N-terminal containing most of the protein coding for GTP binding and hydrolysis. The C-terminal of RhoA is modified via prenylation, anchoring the GTPase into membranes, which is essential for its role in cell growth and cytoskeleton organization. Key amino acids that are involved in the stabilization and regulation of GTP hydrolysis are conserved in RhoA as Gly14, Thr19, Phe30 and Gln63. Correct localization of the RhoA proteins is heavily dependent on the C-terminus; during prenylation, the anchoring of the prenyl group is essential for the stability, inhibition of and the synthesis of enzymes and proliferation. RhoA is sequestered by dissociation inhibitors (RhoGDIs) which remove the protein from the membrane while preventing its further interaction with other downstream effectors. The specific gene that encodes RhoA, ''ARHA'', is located on chromosome 3 and consists of four exons, which has also been linked as a possible risk factor for atherothrombolic stroke. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「RHOA」の詳細全文を読む スポンサード リンク
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