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3.A.5.9.1
Sec-SRP translocase complex. The BAP29 and BAP31 (also called BCAP31) proteins interact directly with the Sec translocon (Wilson & Barlowe et al., 2010).  SRP68 and SRP72 form a complex with SRP RNA and SRP19.  The SRP68 binding site for the RNA is a tetratricopeptide-like module that bends the RNA and inserts an arginine-rich helix into the major groove to open the conserved 5f RNA loop and remodel the RNA for protein translocation (Grotwinkel et al. 2014).  Sec31 (Sec 31L1; HSPC334; HSPC275) is an outer cage component of the coat protein complex II (COPII) machinery which is recruited to specialized regions of the ER, called ER exit sites (ERES), where it plays a central role in the early secretory pathway. Sec31 also interacts with ALG-2 (Programed cell death protein 6 (PDCD6)) and annexin A11 (AnxA11) (Shibata et al. 2015). The Sec61 translocon mediates poorly efficient membrane insertion of Arg-containing TMSs, but a combination of arginine snorkeling, bilayer deformation, and peptide tilting is sufficient to lower the penalty of Arg insertion to an extent that a hydrophobic TMS with a central Arg residue readily inserts into a membrane (Ulmschneider et al. 2017). Mycolactone is a bacterium-derived macrolide that blocks the biogenesis of a large array of secretory and integral transmembrane proteins through potent inhibition of the Sec61 translocon (Morel et al. 2018). The Sec61α subunit possesses an opening between TMS2b and TMS7, the lateral gate, that is the exit for signal sequences and TMSs of translocating polypeptides to the lipid bilayer (Kida and Sakaguchi 2018). BCAP31 (BAP31; 246 aas and 3 N-terminal TMSs) is an ER chaparone that plays a role in the export of secreted proteins in the ER as well as the recognition of abnormally folded protein for targeting to the ER associated-degradation (ERAD) pathway (Wakana et al. 2008). It also serves as a cargo receptor for the export of transmembrane proteins (Annaert et al. 1997). Sec61 is the target of the cytotoxic plant-derived compound, ipomoeassin F (see TC family 8.C.10).

Accession Number:P61011
Protein Name:Signal recognition particle 54 kDa protein aka SRP54
Length:504
Molecular Weight:55705.00
Species:Homo sapiens (Human) [9606]
Location1 / Topology2 / Orientation3: Nucleus speckle1
Substrate protein polypeptide chain

Cross database links:

RefSeq: NP_001139754.1    NP_003127.1   
Entrez Gene ID: 6729   
Pfam: PF00448    PF02881    PF02978   
OMIM: 604857  gene
KEGG: hsa:6729   

Gene Ontology

GO:0016607 C:nuclear speck
GO:0005786 C:signal recognition particle, endoplasmic re...
GO:0008312 F:7S RNA binding
GO:0008144 F:drug binding
GO:0030942 F:endoplasmic reticulum signal peptide binding
GO:0019003 F:GDP binding
GO:0005525 F:GTP binding
GO:0017111 F:nucleoside-triphosphatase activity
GO:0005515 F:protein binding
GO:0043021 F:ribonucleoprotein binding
GO:0042493 P:response to drug
GO:0006616 P:SRP-dependent cotranslational protein targe...
GO:0006617 P:SRP-dependent cotranslational protein targe...

References (8)

[1] “Sequence of the highly conserved gene encoding the human 54kDa subunit of signal recognition particle.”  Patel S.et.al.   8722571
[2] “Protein SRP54 of human signal recognition particle: cloning, expression, and comparative analysis of functional sites.”  Gowda K.et.al.   9511762
[3] “Complete sequencing and characterization of 21,243 full-length human cDNAs.”  Ota T.et.al.   14702039
[4] “The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC).”  The MGC Project Teamet.al.   15489334
[5] “Human RNPS1 and its associated factors: a versatile alternative pre-mRNA splicing regulator in vivo.”  Sakashita E.et.al.   14729963
[6] “Lysine acetylation targets protein complexes and co-regulates major cellular functions.”  Choudhary C.et.al.   19608861
[7] “Crystal structure of the conserved subdomain of human protein SRP54M at 2.1 A resolution: evidence for the mechanism of signal peptide binding.”  Clemons W.M. Jr.et.al.   10497032
[8] “Induced structural changes of 7SL RNA during the assembly of human signal recognition particle.”  Kuglstatter A.et.al.   12244299
Structure:
1MFQ   1QB2   5L3Q     

External Searches:

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Predict TMSs (Predict number of transmembrane segments)
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FASTA formatted sequence
1:	MVLADLGRKI TSALRSLSNA TIINEEVLNA MLKEVCTALL EADVNIKLVK QLRENVKSAI 
61:	DLEEMASGLN KRKMIQHAVF KELVKLVDPG VKAWTPTKGK QNVIMFVGLQ GSGKTTTCSK 
121:	LAYYYQRKGW KTCLICADTF RAGAFDQLKQ NATKARIPFY GSYTEMDPVI IASEGVEKFK 
181:	NENFEIIIVD TSGRHKQEDS LFEEMLQVAN AIQPDNIVYV MDASIGQACE AQAKAFKDKV 
241:	DVASVIVTKL DGHAKGGGAL SAVAATKSPI IFIGTGEHID DFEPFKTQPF ISKLLGMGDI 
301:	EGLIDKVNEL KLDDNEALIE KLKHGQFTLR DMYEQFQNIM KMGPFSQILG MIPGFGTDFM 
361:	SKGNEQESMA RLKKLMTIMD SMNDQELDST DGAKVFSKQP GRIQRVARGS GVSTRDVQEL 
421:	LTQYTKFAQM VKKMGGIKGL FKGGDMSKNV SQSQMAKLNQ QMAKMMDPRV LHHMGGMAGL 
481:	QSMMRQFQQG AAGNMKGMMG FNNM