- Signal recognition particle receptor
Symbol = SRX
Name = SRX
SCOP = 1nrj
OPM family= 145
OPM protein= 1nrj
Signal recognition particle (SRP) receptor also called
docking protein, is a dimercomposed 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 moleculethat helps the ribosome-mRNA- polypeptidecomplexes to settle down on the membrane of the endoplasmic reticulum.
ignal recognition particle (SRP)
The signal recognition particle (SRP) is a multimeric protein, which along with its conjugate receptor (SR), is involved in targeting secretory proteins to the rough endoplasmic reticulum (RER) membrane in eukaryotes, or to the plasma membrane in prokaryotescite journal |author=Stroud RM, Walter P, Rutenber E, Reyes CL |title=X-ray Structures of the Signal Recognition Particle Receptor Reveal Targeting Cycle Intermediates |journal=PLoS ONE |volume=2 |issue= |pages=- |year=2007 |pmid=17622352 |doi=10.1371/journal.pone.0000607] cite journal |author=Dobberstein B, High S, Romisch K, Miller FW |title=Human autoantibodies against the 54 kDa protein of the signal recognition particle block function at multiple stages |journal=Arthritis Res Ther |volume=8 |issue=2 |pages=- |year=2006 |pmid=16469117] . SRP recognises the signal sequence of the nascent polypeptide on the ribosome, retards its elongation, and docks the SRP-ribosome-polypeptide complex to the RER membrane via the SR receptor. SRP consists of six polypeptides (SRP9, SRP14, SRP19, SRP54, SRP68 and SRP72) and a single 300 nucleotide 7S RNA molecule. The RNA component catalyses the interaction ofSRP with its SR receptorcite journal |author=Walter P, Bradshaw N |title=The Signal Recognition Particle (SRP) RNA Links Conformational Changes in the SRP to Protein Targeting |journal=Mol. Biol. Cell |volume=18 |issue=7 |pages=- |year=2007 |pmid=17507650] . In higher eukaryotes, the SRP complex consists of the Alu domain and the S domain linked by the SRP RNA. The Alu domain consists of a heterodimer of SRP9 and SRP14 bound to the 5' and 3' terminal sequences of SRP RNA. This domain is necessary for retarding the elongation of the nascent polypeptide chain, which gives SRP time to dock the ribosome-polypeptide complex to the RER membrane.
The SRP receptor is a monomer consisting of the loosely membrane-associated SR-alpha homologue FtsY, while the eukaryotic SR receptor is a heterodimer of SR-alpha (70 kDa) and SR-beta (25 kDa), both of which contain a GTP-binding domaincite journal |author=Blobel G, Schwartz T |title=Structural basis for the function of the beta subunit of the eukaryotic signal recognition particle receptor |journal=Cell |volume=112 |issue=6 |pages=- |year=2003 |pmid=12654246] . SR-alpha regulates the targeting of SRP-ribosome-nascent polypeptide complexes to the transloconcite journal |author=Andrews DW, Legate KR, Falcone D |title=Nucleotide-dependent binding of the GTPase domain of the signal recognition particle receptor beta-subunit to the alpha-subunit |journal=J. Biol. Chem. |volume=275 |issue=35 |pages=- |year=2000 |pmid=10859309] . 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 membranecite journal |author=Walter P, Miller JD, Tajima S, Lauffer L |title=The beta subunit of the signal recognition particle receptor is a transmembrane GTPase that anchors the alpha subunit, a peripheral membrane GTPase, to the endoplasmic reticulum membrane |journal=J. Cell Biol. |volume=128 |issue=3 |pages=- |year=1995 |pmid=7844142] . 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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