scholarly journals Cotranslational Intersection between the SRP and GET Targeting Pathways to the Endoplasmic Reticulum of Saccharomyces cerevisiae

2016 ◽  
Vol 36 (18) ◽  
pp. 2374-2383 ◽  
Author(s):  
Ying Zhang ◽  
Thea Schäffer ◽  
Tina Wölfle ◽  
Edith Fitzke ◽  
Gerhard Thiel ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Endoplasmic Reticulum ◽  
Transmembrane Domain ◽  
Signal Recognition Particle ◽  
Transmembrane Proteins ◽  
Signal Recognition ◽  
Ribosome Binding ◽  
Channel Proteins ◽  
Membrane Spanning ◽  
Combined Data

Targeting of transmembrane proteins to the endoplasmic reticulum (ER) proceeds via either the signal recognition particle (SRP) or the guided entry of tail-anchored proteins (GET) pathway, consisting of Get1 to -5 and Sgt2. While SRP cotranslationally targets membrane proteins containing one or multiple transmembrane domains, the GET pathway posttranslationally targets proteins containing a single C-terminal transmembrane domain termed the tail anchor. Here, we dissect the roles of the SRP and GET pathways in the sorting of homologous, two-membrane-spanning K+channel proteins termed Kcv, Kesv, and Kesv-VV. We show that Kcv is targeted to the ER cotranslationally via its N-terminal transmembrane domain, while Kesv-VV is targeted posttranslationally via its C-terminal transmembrane domain, which recruits Get4-5/Sgt2 and Get3. Unexpectedly, nascent Kcv recruited not only SRP but also the Get4-5 module of the GET pathway to ribosomes. Ribosome binding of Get4-5 was independent of Sgt2 and was strongly outcompeted by SRP. The combined data indicate a previously unrecognized cotranslational interplay between the SRP and GET pathways.

scholarly journals NAC functions as a modulator of SRP during the early steps of protein targeting to the endoplasmic reticulum

2012 ◽  
Vol 23 (16) ◽  
pp. 3027-3040 ◽  
Author(s):  
Ying Zhang ◽  
Uta Berndt ◽  
Hanna Gölz ◽  
Arlette Tais ◽  
Stefan Oellerer ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Targeting ◽  
Signal Sequence ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Signal Sequences ◽  
Chain Complexes ◽  
Ribosomal Tunnel ◽  
Nascent Chain ◽  
Combined Data

Nascent polypeptide-associated complex (NAC) was initially found to bind to any segment of the nascent chain except signal sequences. In this way, NAC is believed to prevent mistargeting due to binding of signal recognition particle (SRP) to signalless ribosome nascent chain complexes (RNCs). Here we revisit the interplay between NAC and SRP. NAC does not affect SRP function with respect to signalless RNCs; however, NAC does affect SRP function with respect to RNCs targeted to the endoplasmic reticulum (ER). First, early recruitment of SRP to RNCs containing a signal sequence within the ribosomal tunnel is NAC dependent. Second, NAC is able to directly and tightly bind to nascent signal sequences. Third, SRP initially displaces NAC from RNCs; however, when the signal sequence emerges further, trimeric NAC·RNC·SRP complexes form. Fourth, upon docking to the ER membrane NAC remains bound to RNCs, allowing NAC to shield cytosolically exposed nascent chain domains not only before but also during cotranslational translocation. The combined data indicate a functional interplay between NAC and SRP on ER-targeted RNCs, which is based on the ability of the two complexes to bind simultaneously to distinct segments of a single nascent chain.

scholarly journals An alternative pathway for membrane protein biogenesis at the endoplasmic reticulum

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Sarah O’Keefe ◽  
Guanghui Zong ◽  
Kwabena B. Duah ◽  
Lauren E. Andrews ◽  
Wei Q. Shi ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Alternative Pathway ◽  
Signal Recognition Particle ◽  
Transmembrane Proteins ◽  
Signal Recognition ◽  
Major Site ◽  
Type Iii ◽  
Membrane Complex ◽  
Protein Biogenesis

AbstractThe heterotrimeric Sec61 complex is a major site for the biogenesis of transmembrane proteins (TMPs), accepting nascent TMP precursors that are targeted to the endoplasmic reticulum (ER) by the signal recognition particle (SRP). Unlike most single-spanning membrane proteins, the integration of type III TMPs is completely resistant to small molecule inhibitors of the Sec61 translocon. Using siRNA-mediated depletion of specific ER components, in combination with the potent Sec61 inhibitor ipomoeassin F (Ipom-F), we show that type III TMPs utilise a distinct pathway for membrane integration at the ER. Hence, following SRP-mediated delivery to the ER, type III TMPs can uniquely access the membrane insertase activity of the ER membrane complex (EMC) via a mechanism that is facilitated by the Sec61 translocon. This alternative EMC-mediated insertion pathway allows type III TMPs to bypass the Ipom-F-mediated blockade of membrane integration that is seen with obligate Sec61 clients.

scholarly journals Ribosome Binding to and Dissociation from Translocation Sites of the Endoplasmic Reticulum Membrane

2006 ◽  
Vol 17 (9) ◽  
pp. 3860-3869 ◽  
Author(s):  
Julia Schaletzky ◽  
Tom A. Rapoport
Keyword(s):  
Endoplasmic Reticulum ◽  
Binding Sites ◽  
Signal Recognition Particle ◽  
Structural Data ◽  
Endoplasmic Reticulum Membrane ◽  
Signal Recognition ◽  
Ribosome Binding ◽  
High Affinity ◽  
Chain Complexes ◽  
Nascent Chain

We have addressed how ribosome-nascent chain complexes (RNCs), associated with the signal recognition particle (SRP), can be targeted to Sec61 translocation channels of the endoplasmic reticulum (ER) membrane when all binding sites are occupied by nontranslating ribosomes. These competing ribosomes are known to be bound with high affinity to tetramers of the Sec61 complex. We found that the membrane binding of RNC–SRP complexes does not require or cause the dissociation of prebound nontranslating ribosomes, a process that is extremely slow. SRP and its receptor target RNCs to a free population of Sec61 complex, which associates with nontranslating ribosomes only weakly and is conformationally different from the population of ribosome-bound Sec61 complex. Taking into account recent structural data, we propose a model in which SRP and its receptor target RNCs to a Sec61 subpopulation of monomeric or dimeric state. This could explain how RNC–SRP complexes can overcome the competition by nontranslating ribosomes.

scholarly journals Hierarchical regulation of mRNA partitioning between the cytoplasm and the endoplasmic reticulum of mammalian cells

2011 ◽  
Vol 22 (14) ◽  
pp. 2646-2658 ◽  
Author(s):  
Qiang Chen ◽  
Sujatha Jagannathan ◽  
David W. Reid ◽  
Tianli Zheng ◽  
Christopher V. Nicchitta
Keyword(s):  
Endoplasmic Reticulum ◽  
Mammalian Cells ◽  
Secretory Pathway ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Endomembrane System ◽  
Genomic Analyses ◽  
Specific Manner ◽  
Signal Encoding ◽  
Mrna Transcriptome

The mRNA transcriptome is currently thought to be partitioned between the cytosol and endoplasmic reticulum (ER) compartments by binary selection; mRNAs encoding cytosolic/nucleoplasmic proteins are translated on free ribosomes, and mRNAs encoding topogenic signal-bearing proteins are translated on ER-bound ribosomes, with ER localization being conferred by the signal-recognition particle pathway. In subgenomic and genomic analyses of subcellular mRNA partitioning, we report an overlapping subcellular distribution of cytosolic/nucleoplasmic and topogenic signal-encoding mRNAs, with mRNAs of both cohorts displaying noncanonical subcellular partitioning patterns. Unexpectedly, the topogenic signal-encoding mRNA transcriptome was observed to partition in a hierarchical, cohort-specific manner. mRNAs encoding resident proteins of the endomembrane system were clustered at high ER-enrichment values, whereas mRNAs encoding secretory pathway cargo were broadly represented on free and ER-bound ribosomes. Two distinct modes of mRNA association with the ER were identified. mRNAs encoding endomembrane-resident proteins were bound via direct, ribosome-independent interactions, whereas mRNAs encoding secretory cargo displayed predominantly ribosome-dependent modes of ER association. These data indicate that mRNAs are partitioned between the cytosol and ER compartments via a hierarchical system of intrinsic and encoded topogenic signals and identify mRNA cohort-restricted modes of mRNA association with the ER.

scholarly journals Saccharomyces cerevisiae and Schizosaccharomyces pombe contain a homologue to the 54-kD subunit of the signal recognition particle that in S. cerevisiae is essential for growth.

1989 ◽  
Vol 109 (6) ◽  
pp. 3223-3230 ◽  
Author(s):  
B C Hann ◽  
M A Poritz ◽  
P Walter
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Schizosaccharomyces Pombe ◽  
Dna Sequences ◽  
Consensus Sequence ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Protein Subunit ◽  
Reading Frame ◽  
Conserved Sequence ◽  
Yeast Genes

We have isolated and sequenced genes from Saccharomyces cerevisiae (SRP54SC) and Schizosaccharomyces pombe (SRP54sp) encoding proteins homologous to both the 54-kD protein subunit (SRP54mam) of the mammalian signal recognition particle (SRP) and the product of a gene of unknown function in Escherichia coli, ffh (Römisch, K., J. Webb, J. Herz, S. Prehn, R. Frank, M. Vingron, and B. Dobberstein. 1989. Nature (Lond.). 340:478-482; Bernstein H. D., M. A. Poritz, K. Strub, P. J. Hoben, S. Brenner, P. Walter. 1989. Nature (Lond.). 340:482-486). To accomplish this we took advantage of short stretches of conserved sequence between ffh and SRP54mam and used the polymerase chain reaction (PCR) to amplify fragments of the homologous yeast genes. The DNA sequences predict proteins for SRP54sc and SRP54sp that are 47% and 52% identical to SRP54mam, respectively. Like SRP54mam and ffh, both predicted yeast proteins contain a GTP binding consensus sequence in their NH2-terminal half (G-domain), and methionine-rich sequences in their COOH-terminal half (M-domain). In contrast to SRP54mam and ffh the yeast proteins contain additional Met-rich sequences inserted at the COOH-terminal portion of the M-domain. SRP54sp contains a 480-nucleotide intron located 78 nucleotides from the 5' end of the open reading frame. Although the function of the yeast homologues is unknown, gene disruption experiments in S. cerevisiae show that the gene is essential for growth. The identification of SRP54sc and SRP54sp provides the first evidence for SRP related proteins in yeast.

scholarly journals Early encounters of a nascent membrane protein

2005 ◽  
Vol 170 (1) ◽  
pp. 27-35 ◽  
Author(s):  
Edith N.G. Houben ◽  
Raz Zarivach ◽  
Bauke Oudega ◽  
Joen Luirink
Keyword(s):  
Membrane Protein ◽  
Ribosomal Proteins ◽  
Transmembrane Domain ◽  
Signal Recognition Particle ◽  
Chain Complex ◽  
Signal Recognition ◽  
Inner Membrane ◽  
Ribosomal Tunnel ◽  
Nascent Chain ◽  
Inner Membrane Protein

An unbiased photo–cross-linking approach was used to probe the “molecular path” of a growing nascent Escherichia coli inner membrane protein (IMP) from the peptidyl transferase center to the surface of the ribosome. The nascent chain was initially in proximity to the ribosomal proteins L4 and L22 and subsequently contacted L23, which is indicative of progression through the ribosome via the main ribosomal tunnel. The signal recognition particle (SRP) started to interact with the nascent IMP and to target the ribosome–nascent chain complex to the Sec–YidC complex in the inner membrane when maximally half of the transmembrane domain (TM) was exposed from the ribosomal exit. The combined data suggest a flexible tunnel that may accommodate partially folded nascent proteins and parts of the SRP and SecY. Intraribosomal contacts of the nascent chain were not influenced by the presence of a functional TM in the ribosome.

scholarly journals GTP-binding proteins may stimulate insulin biosynthesis in rat pancreatic islets by enhancing the signal-recognition-particle-dependent translocation of the insulin mRNA poly-/mono-some complex to the endoplasmic reticulum

1991 ◽  
Vol 275 (1) ◽  
pp. 23-28 ◽  
Author(s):  
N Welsh ◽  
C Oberg ◽  
M Welsh
Keyword(s):  
Endoplasmic Reticulum ◽  
Binding Proteins ◽  
Specific Binding ◽  
Signal Recognition Particle ◽  
Insulin Biosynthesis ◽  
Signal Recognition ◽  
Insulin Synthesis ◽  
Gtp Binding Proteins ◽  
Gtp Binding ◽  
Insulin Mrna

We aimed to elucidate the putative role of GTP-binding proteins in the regulation of insulin biosynthesis. For this purpose, freshly isolated rat islets were incubated in the presence of liposomes containing GDP, guanosine 5′-[beta-thio]diphosphate (GDP[S]), GTP, guanosine 5′-[gamma-thio]triphosphate (GTP[S]), guanosine 5′-[beta gamma-methylene]triphosphate (p[CH2]ppG), guanosine 5′[beta gamma-imido]triphosphate (p[NH]ppG) and ATP, and the effects of the liposomal delivery of these substances on rates of biosynthesis of insulin and total protein were determined. Insulin biosynthesis during a 1 h incubation at 1.67 mM-glucose was stimulated by ATP- and GTP[S]-containing liposomes as compared with control liposomes. At 16.7 mM-glucose, only the GTP[S]-containing liposomes stimulated insulin biosynthesis. No inhibition of islet protein and insulin synthesis was observed with GDP-, GDP[S]-, p[CH2]ppG- and p[NH]ppG-containing liposomes. By determining the subcellular distribution of insulin mRNA, it was found that the mRNA content associated with microsomes was increased and that associated with the cytosolic mono-/poly-somes decreased when the islets were incubated with GTP[S]-containing liposomes, resulting in an approximate doubling of the ratio of microsomal to polysomal-associated insulin mRNA. ATP-containing liposomes produced no effects on the association of insulin mRNA with microsomes. By using photoaffinity labelling and immunoprecipitation techniques, specific binding of GTP[35S] to the alpha-subunit of the signal-recognition particle (SRP) receptor in islet homogenates containing physiological concentrations of GTP and GDP was demonstrated. These findings suggest that the GTP-binding subunit(s) of the SRP receptor, and possibly also of other GTP-binding proteins involved in this process, may regulate insulin biosynthesis by stimulating the translocation of insulin mRNA to the endoplasmic reticulum and by increasing preproinsulin-peptide translocation into the lumen of the reticulum.

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