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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:P39742
Protein Name:Sec72 aka SEC67 aka SIM2 aka YLR292C aka L8003.18
Length:193
Molecular Weight:21607.00
Species:Saccharomyces cerevisiae (Baker's yeast) [4932]
Location1 / Topology2 / Orientation3: Cytoplasm1
Substrate protein

Cross database links:

DIP: DIP-2491N
RefSeq: NP_013395.1   
Entrez Gene ID: 850999   
KEGG: sce:YLR292C   

Gene Ontology

GO:0031207 C:Sec62/Sec63 complex
GO:0005515 F:protein binding
GO:0008565 F:protein transporter activity
GO:0031204 P:posttranslational protein targeting to memb...

References (10)

[1] “Sec72p contributes to the selective recognition of signal peptides by the secretory polypeptide translocation complex.”  Feldheim D.et.al.   8051213
[2] “Evidence that GCD6 and GCD7, translational regulators of GCN4, are subunits of the guanine nucleotide exchange factor for eIF-2 in Saccharomyces cerevisiae.”  Bushman J.L.et.al.   8441423
[3] “The nucleotide sequence of Saccharomyces cerevisiae chromosome XII.”  Johnston M.et.al.   9169871
[4] “Approaching a complete repository of sequence-verified protein-encoding clones for Saccharomyces cerevisiae.”  Hu Y.et.al.   17322287
[5] “GSP1 and GSP2, genetic suppressors of the prp20-1 mutant in Saccharomyces cerevisiae: GTP-binding proteins involved in the maintenance of nuclear organization.”  Belhumeur P.et.al.   8455603
[6] “A Sec63p-BiP complex from yeast is required for protein translocation in a reconstituted proteoliposome.”  Brodsky J.L.et.al.   8253836
[7] “Assembly of yeast Sec proteins involved in translocation into the endoplasmic reticulum into a membrane-bound multisubunit complex.”  Deshaies R.J.et.al.   2000150
[8] “Posttranslational protein transport in yeast reconstituted with a purified complex of Sec proteins and Kar2p.”  Panzner S.et.al.   7758110
[9] “Global analysis of protein expression in yeast.”  Ghaemmaghami S.et.al.   14562106
[10] “Identification of novel protein-protein interactions at the cytosolic surface of the Sec63 complex in the yeast ER membrane.”  Willer M.et.al.   12518317
Structure:
6N3Q   6ND1     

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FASTA formatted sequence
1:	MVTLEYNANS KLITASDAVV ALSTETNIDQ INVLTTSLIG ETNPNFTPQP NEALSKMIKG 
61:	LFESGMKNLQ QKKLNEALKN VSLAIEMAQR KRAPWEAFAI QLPELHFMLR SKIDLCLILG 
121:	KHLEALQDLD FLLGTGLIQP DVFVRKADCL LKLRQWEEAR ATCERGLALA PEDMKLRALL 
181:	IETARNLAEY NGE