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3.A.5.8.1
The general secretory pathway (Sec-SRP) complex. The Yet1 and Yet3 proteins interact directly with the Sec translocon (Wilson & Barlowe et al., 2010). The Sss1/Sec61γ protein (80aas) has two domains. The cytosolic domain is required for Sec61p interaction while the transmembrane clamp domain is required to complete activation of the translocon after precursor targeting to Sec61p (Wilkinson et al., 2010). However, the apolar surfrace area determines the efficiency of translocon-mediated membrane-protein integration into the endoplasmic reticulum (Öjemalm et al., 2011). The essential Sec62, Sec63 and non-essential Sec66 and Sec72 proteins may comprise an SRP-independent tetrameric translocon enlisting the lumenal chaperone, BiP/Kar2 to ""ratchet"" its substrates into the ER (Feldheim and Schekman 1994; Ast et al. 2013). Cytosolic segments of the Sec61 complex important for promoting the structural transition between the closed and open conformations of the complex have been identified (Mandon et al. 2018). Positively charged residues in multiple cytosolic segments, as well as bulky hydrophobic residues in the L6/7-TMS7 junction may be required for cotranslational translocation or integration of membrane proteins by the Sec61 complex (Mandon et al. 2018). The structure of the yeast post-translational Sec complex (Sec61-Sec63-Sec71-Sec72) by cryo-EM shows that Sec63 tightly associates with Sec61 through interactions in cytosolic, transmembrane, and ER-luminal domains, prying open Sec61's lateral gate and translocation pore, and thus activating the channel for substrate engagement.  Sec63 optimally positions binding sites for cytosolic and luminal chaperones in the complex to enable efficient polypeptide translocation (Itskanov and Park 2019). Further, post-translational translocation is mediated by the association of the Sec61 channel with the membrane protein complex, the Sec62-Sec63 complex, and substrates move through the channel by the luminal BiP ATPase. Wu et al. 2019 determined the cryoEM structure of the S. cerevisiae Sec complex, consisting of the Sec61 channel and the Sec62, Sec63, Sec71 and Sec72 proteins. Sec63 causes wide opening of the lateral gate of the Sec61 channel, priming it for the passage of low-hydrophobicity signal sequences into the lipid phase, without displacing the channel's plug domain. Lateral channel opening is triggered by Sec63 interacting both with cytosolic loops in the C-terminal half of Sec61 and transmembrane segments in the N-terminal half of the Sec61 channel. The cytosolic Brl domain of Sec63 blocks ribosome binding to the channel and recruits Sec71 and Sec72, positioning them for the capture of polypeptides associated with cytosolic Hsp70. The structure thus shows how the Sec61 channel is activated for post-translational protein translocation (Wu et al. 2019).

Accession Number:P32916
Protein Name:SRP receptor aka SRP101 aka YDR292C aka D9819.3
Length:621
Molecular Weight:69278.00
Species:Saccharomyces cerevisiae (Baker's yeast) [4932]
Location1 / Topology2 / Orientation3: Endoplasmic reticulum membrane1 / Peripheral membrane protein2 / Cytoplasmic side3
Substrate protein

Cross database links:

DIP: DIP-1672N
RefSeq: NP_010578.1   
Entrez Gene ID: 851886   
Pfam: PF00448    PF02881    PF09201   
KEGG: sce:YDR292C   

Gene Ontology

GO:0005785 C:signal recognition particle receptor complex
GO:0005525 F:GTP binding
GO:0017111 F:nucleoside-triphosphatase activity
GO:0005515 F:protein binding
GO:0004872 F:receptor activity
GO:0005047 F:signal recognition particle binding
GO:0006614 P:SRP-dependent cotranslational protein targe...

References (6)

[1] “Signal recognition particle receptor is important for cell growth and protein secretion in Saccharomyces cerevisiae.”  Ogg S.C.et.al.   1327299
[2] “The nucleotide sequence of Saccharomyces cerevisiae chromosome IV.”  Jacq C.et.al.   9169867
[3] “A functional GTPase domain, but not its transmembrane domain, is required for function of the SRP receptor beta-subunit.”  Ogg S.C.et.al.   9679135
[4] “Global analysis of protein expression in yeast.”  Ghaemmaghami S.et.al.   14562106
[5] “A multidimensional chromatography technology for in-depth phosphoproteome analysis.”  Albuquerque C.P.et.al.   18407956
[6] “Structural basis for the function of the beta subunit of the eukaryotic signal recognition particle receptor.”  Schwartz T.et.al.   12654246
Structure:
1NRJ     

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Predict TMSs (Predict number of transmembrane segments)
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FASTA formatted sequence
1:	MFDQLAVFTP QGQVLYQYNC LGKKFSEIQI NSFISQLITS PVTRKESVAN ANTDGFDFNL 
61:	LTINSEHKNS PSFNALFYLN KQPELYFVVT FAEQTLELNQ ETQQTLALVL KLWNSLHLSE 
121:	SILKNRQGQN EKNKHNYVDI LQGIEDDLKK FEQYFRIKYE ESIKQDHINP DNFTKNGSVP 
181:	QSHNKNTKKK LRDTKGKKQS TGNVGSGRKW GRDGGMLDEM NHEDAAKLDF SSSNSHNSSQ 
241:	VALDSTINKD SFGDRTEGGD FLIKEIDDLL SSHKDEITSG NEAKNSGYVS TAFGFLQKHV 
301:	LGNKTINESD LKSVLEKLTQ QLITKNVAPE AADYLTQQVS HDLVGSKTAN WTSVENTARE 
361:	SLTKALTQIL TPGVSVDLLR EIQSKRSKKD EEGKCDPYVF SIVGVNGVGK STNLSKLAFW 
421:	LLQNNFKVLI VACDTFRSGA VEQLRVHVEN LAQLMDDSHV RGSKNKRGKT GNDYVELFEA 
481:	GYGGSDLVTK IAKQAIKYSR DQNFDIVLMD TAGRRHNDPT LMSPLKSFAD QAKPDKIIMV 
541:	GEALVGTDSV QQAKNFNDAF GKGRNLDFFI ISKCDTVGEM LGTMVNMVYA TGIPILFVGV 
601:	GQTYTDLRTL SVKWAVNTLM S