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SRP receptor : ウィキペディア英語版 | Signal recognition particle receptor
Signal recognition particle (SRP) receptor, also called docking protein, is a dimer composed of 2 different subunits that are associated exclusively with the rough ER in mammalian cells. Its main function is to identify the SRP units. SRP (signal recognition particle) is a molecule that helps the ribosome-mRNA-polypeptide complexes to settle down on the membrane of the endoplasmic reticulum. ==SRP receptor== The eukaryotic SRP receptor (termed SR) is a heterodimer of SR-alpha (70 kDa) and SR-beta (25 kDa), both of which contain a GTP-binding domain, while the prokaryotic SRP receptor comprises only the monomeric loosely membrane-associated SR-alpha homologue FtsY. SR-alpha regulates the targeting of SRP-ribosome-nascent polypeptide complexes to the translocon. SR-alpha binds to the SRP54 subunit of the SRP complex. The SR-beta subunit is a transmembrane GTPase that anchors the SR-alpha subunit (a peripheral membrane GTPase) to the ER membrane. SR-beta interacts with the N-terminal SRX-domain of SR-alpha, which is not present in the bacterial FtsY homologue. SR-beta also functions in recruiting the SRP-nascent polypeptide to the protein-conducting channel. This family represents homologues of the alpha subunit of the SR receptor. Members of this entry consist of a central six-stranded anti-parallel beta-sheet sandwiched by helix alpha1 on one side and helices alpha2-alpha4 on the other. They interact with the small GTPase SR-beta, forming a complex that matches a class of small G protein-effector complexes, including Rap-Raf, Ras-PI3K(gamma), Ras-RalGDS, and Arl2-PDE(delta).〔
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