Protein transport into the human ER and related diseases, Sec61-channelopathies

2014 ◽  
Vol 92 (6) ◽  
pp. 499-509 ◽  
Author(s):  
Sarah Haßdenteufel ◽  
Marie-Christine Klein ◽  
Armin Melnyk ◽  
Richard Zimmermann
Keyword(s):  
Endoplasmic Reticulum ◽  
Molecular Chaperone ◽  
Protein Transport ◽  
Dynamic Equilibrium ◽  
Signal Peptides ◽  
Conducting Channel ◽  
Amino Terminal ◽  
Calcium Storage ◽  
Storage Organelle ◽  
Er Membrane

Protein transport into the human endoplasmic reticulum (ER) is relevant to the biogenesis of most soluble and membrane proteins of organelles, which are involved in endo- or exo-cytsosis. It involves amino-terminal signal peptides in the precursor polypeptides and various transport components in the cytosol plus the ER, and can occur co- or post-translationally. The two mechanisms merge at the level of the ER membrane, specifically at the level of the heterotrimeric Sec61 complex, which forms a dynamic polypeptide-conducting channel in the ER membrane. Since the mammalian ER is also the main intracellular calcium storage organelle, and the Sec61 complex is calcium permeable, the Sec61 complex is tightly regulated in its equilibrium between the closed and open conformations, or “gated”, by ligands, such as signal peptides of the transport substrates and the ER lumenal Hsp70-type molecular chaperone BiP. Furthermore, BiP binding to the incoming polypeptide contributes to the efficiency and unidirectionality of transport. Recent insights into the structure and dynamic equilibrium of the Sec61 complex have various mechanistic as well as medical implications.

scholarly journals Two Endoplasmic Reticulum (ER) Membrane Proteins That Facilitate ER-to-Golgi Transport of Glycosylphosphatidylinositol-anchored Proteins

1999 ◽  
Vol 10 (4) ◽  
pp. 1043-1059 ◽  
Author(s):  
Wolfgang P. Barz ◽  
Peter Walter
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Secretory Pathway ◽  
Protein Transport ◽  
Protein Translocation ◽  
Sequence Similarity ◽  
Surface Proteins ◽  
Golgi Transport ◽  
Er Membrane

Many eukaryotic cell surface proteins are anchored in the lipid bilayer through glycosylphosphatidylinositol (GPI). GPI anchors are covalently attached in the endoplasmic reticulum (ER). The modified proteins are then transported through the secretory pathway to the cell surface. We have identified two genes inSaccharomyces cerevisiae, LAG1 and a novel gene termed DGT1 (for “delayed GPI-anchored protein transport”), encoding structurally related proteins with multiple membrane-spanning domains. Both proteins are localized to the ER, as demonstrated by immunofluorescence microscopy. Deletion of either gene caused no detectable phenotype, whereas lag1Δ dgt1Δ cells displayed growth defects and a significant delay in ER-to-Golgi transport of GPI-anchored proteins, suggesting thatLAG1 and DGT1 encode functionally redundant or overlapping proteins. The rate of GPI anchor attachment was not affected, nor was the transport rate of several non–GPI-anchored proteins. Consistent with a role of Lag1p and Dgt1p in GPI-anchored protein transport, lag1Δ dgt1Δ cells deposit abnormal, multilayered cell walls. Both proteins have significant sequence similarity to TRAM, a mammalian membrane protein thought to be involved in protein translocation across the ER membrane. In vivo translocation studies, however, did not detect any defects in protein translocation in lag1Δ dgt1Δcells, suggesting that neither yeast gene plays a role in this process. Instead, we propose that Lag1p and Dgt1p facilitate efficient ER-to-Golgi transport of GPI-anchored proteins.

scholarly journals EMC1-dependent stabilization drives membrane penetration of a partially destabilized non-enveloped virus

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Parikshit Bagchi ◽  
Takamasa Inoue ◽  
Billy Tsai
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Membrane Transport ◽  
Molecular Chaperone ◽  
Viral Particle ◽  
The Novel ◽  
Membrane Penetration ◽  
Membrane Protein Complex ◽  
Enveloped Virus ◽  
Er Membrane

Destabilization of a non-enveloped virus generates a membrane transport-competent viral particle. Here we probe polyomavirus SV40 endoplasmic reticulum (ER)-to-cytosol membrane transport, a decisive infection step where destabilization initiates this non-enveloped virus for membrane penetration. We find that a member of the ER membrane protein complex (EMC) called EMC1 promotes SV40 ER membrane transport and infection. Surprisingly, EMC1 does so by using its predicted transmembrane residue D961 to bind to and stabilize the membrane-embedded partially destabilized SV40, thereby preventing premature viral disassembly. EMC1-dependent stabilization enables SV40 to engage a cytosolic extraction complex that ejects the virus into the cytosol. Thus EMC1 acts as a molecular chaperone, bracing the destabilized SV40 in a transport-competent state. Our findings reveal the novel principle that coordinated destabilization-stabilization drives membrane transport of a non-enveloped virus.

Endoplasmic reticulum contains a common, abundant calcium-binding glycoprotein, endoplasmin

1986 ◽  
Vol 86 (1) ◽  
pp. 217-232 ◽  
Author(s):  
G. Koch ◽  
M. Smith ◽  
D. Macer ◽  
P. Webster ◽  
R. Mortara
Keyword(s):  
Endoplasmic Reticulum ◽  
Calcium Binding ◽  
Mammalian Cells ◽  
Terminal Sequence ◽  
Binding Studies ◽  
Amino Terminal ◽  
Calcium Storage ◽  
Amino Terminal Sequence ◽  
Binding Glycoprotein ◽  
In Cells

The most abundant protein in microsomal membrane preparations from mammalian cells has been identified as a 100 X 10(3) Mr concanavalin A-binding glycoprotein. The glycosyl moiety of the glycoprotein is completely sensitive to endoglycosidase H, suggesting a predominantly endoplasmic reticulum localization in the cell. Using a monospecific antibody it was shown by binding and immunofluorescence studies that the glycoprotein is intracellular. Immunoelectron microscopy showed that the glycoprotein was at least 100 times more concentrated in the endoplasmic reticulum than in any other cellular organelle. It was found to be substantially overexpressed in cells and tissues rich in endoplasmic reticulum. Since it is the major common protein component associated with the endoplasmic reticulum we refer to it as endoplasmin. Calcium-binding studies show that endoplasmin is a major calcium-binding protein in cells, suggesting that at least one of its roles might be in the calcium-storage function of the endoplasmic reticulum. The amino-terminal sequence of endoplasmin is identical to that of a 100 X 10(3) Mr stress-related protein.

Mitochondrial import: properties of precursor proteins

1990 ◽  
Vol 68 (1) ◽  
pp. 9-16 ◽  
Author(s):  
Ilona Skerjanc
Keyword(s):  
Protein Unfolding ◽  
Protein Transport ◽  
Membrane Surface ◽  
Consensus Sequence ◽  
Signal Peptides ◽  
Mitochondrial Import ◽  
Final Destination ◽  
Amino Terminal ◽  
Lipid Surface ◽  
Shock Proteins

Most mitochondrial proteins are synthesized in the cytoplasm as higher molecular weight precursors and must cross at least one membrane to reach their final destination. Amino-terminal extensions of the precursors, termed signal peptides, have been shown to contain the necessary targeting information. Although no consensus sequence has been determined for signal peptides, all peptides examined to date have been shown to have membrane surface-seeking properties. The evidence so far seems to be consistent with a model in which the precursor initially associates with the lipids of the outer membrane and uses this surface to enhance subsequent diffusion to the import apparatus, thus modulating the overall rate of import. Precursors must at least partially unfold during import, although the extent and mechanism of unfolding remain unclear. The major possible mechanisms of unfolding include spontaneous unfolding of the precursor after engaging the translocation apparatus, ATP-dependent unfolding by a cytosolic factor (possibly the 70-kilodalton heat-shock proteins), and unfolding on the lipid surface of the outer mitochondrial membrane. It is possible that different types of precursors may utilize one or all of these mechanisms, in accordance with their individual needs.Key words: mitochondrial import, targeting sequences, protein transport, protein unfolding, amphiphilic.

scholarly journals Inhibition of endoplasmic reticulum (ER)-to-Golgi transport induces relocalization of binding protein (BiP) within the ER to form the BiP bodies.

1994 ◽  
Vol 5 (10) ◽  
pp. 1129-1143 ◽  
Author(s):  
S Nishikawa ◽  
A Hirata ◽  
A Nakano
Keyword(s):  
Endoplasmic Reticulum ◽  
Secretory Pathway ◽  
Protein Transport ◽  
Binding Protein ◽  
Yeast Cells ◽  
Restrictive Temperature ◽  
Golgi Transport ◽  
Coa Reductase ◽  
Vacuolar Protein ◽  
Er Membrane

Immunofluorescence staining of yeast cells with anti-binding protein (BiP) antibodies shows uniform staining of the endoplasmic reticulum (ER). We have found that overproduction of Sec12p, an ER membrane protein, causes a change of BiP distribution within the cell. Upon induction of Sec12p by the GAL1 promoter, the staining pattern of BiP turns into bright dots scattering in the cell, whereas the staining of Sec12p remains to be the typical ER figure. Overproduction of other ER membrane proteins, HMG-CoA reductase or Sed4 protein, does not induce such relocalization of BiP. Pulse-chase experiments and electron microscopy have revealed that the overproduction of Sec12p inhibits protein transport from the ER to the Golgi apparatus. When the transport is arrested by one of the sec mutations that block the ER-to-Golgi step at the restrictive temperature, the BiP staining also changes into the punctate pattern. In contrast, the sec mutants that block later or earlier steps of the secretory pathway do not induce such change of BiP localization. These observations indicate that relocalization of BiP is caused by the inhibition of ER-to-Golgi transport. Using immunoelectron microscopy, we have found that the punctate staining is because of the accumulation of BiP in the restricted region of the ER, which we propose to call the "BiP body." This implicates existence of ER subdomains in yeast. A vacuolar protein, proteinase A, appears to colocalize in the BiP body when the ER-to-Golgi transport is blocked, suggesting that the BiP body may have a role as the site of accumulation of cargo molecules before exit from the ER.

Surfing the Sec61 channel: bidirectional protein translocation across the ER membrane

1999 ◽  
Vol 112 (23) ◽  
pp. 4185-4191 ◽  
Author(s):  
K. Romisch
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Proteins ◽  
Signal Peptide ◽  
Protein Translocation ◽  
Transmembrane Proteins ◽  
Retrograde Transport ◽  
Conducting Channel ◽  
Peptide Cleavage ◽  
Sec61 Channel ◽  
Er Membrane

Misfolded secretory and transmembrane proteins are retained in the endoplasmic reticulum (ER) and subsequently degraded. Degradation is primarily mediated by cytosolic proteasomes and thus requires retrograde transport out of the ER back to the cytosol. The available evidence suggests that the protein-conducting channel formed by the Sec61 complex is responsible for both forward and retrograde transport of proteins across the ER membrane. For transmembrane proteins, retrograde transport can be viewed as a reversal of integration of membrane proteins into the ER membrane. Retrograde transport of soluble proteins through the Sec61 channel after signal-peptide cleavage, however, must be mechanistically distinct from signal-peptide-mediated import into the ER through the same channel.

scholarly journals Evolutionary Gain of Function for the ER Membrane Protein Sec62 from Yeast to Humans

2010 ◽  
Vol 21 (5) ◽  
pp. 691-703 ◽  
Author(s):  
Linda Müller ◽  
Maria Diaz de Escauriaza ◽  
Patrick Lajoie ◽  
Melanie Theis ◽  
Martin Jung ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Binding Sites ◽  
Protein Transport ◽  
Evolutionary Conservation ◽  
Additional Function ◽  
Ribosomal Tunnel ◽  
Protein Biogenesis ◽  
Precursor Proteins ◽  
Er Membrane

Because of similarity to their yeast orthologues, the two membrane proteins of the human endoplasmic reticulum (ER) Sec62 and Sec63 are expected to play a role in protein biogenesis in the ER. We characterized interactions between these two proteins as well as the putative interaction of Sec62 with ribosomes. These data provide further evidence for evolutionary conservation of Sec62/Sec63 interaction. In addition, they indicate that in the course of evolution Sec62 of vertebrates has gained an additional function, the ability to interact with the ribosomal tunnel exit and, therefore, to support cotranslational mechanisms such as protein transport into the ER. This view is supported by the observation that Sec62 is associated with ribosomes in human cells. Thus, the human Sec62/Sec63 complex and the human ER membrane protein ERj1 are similar in providing binding sites for BiP in the ER-lumen and binding sites for ribosomes in the cytosol. We propose that these two systems provide similar chaperone functions with respect to different precursor proteins.

TMCC3 localizes at the three-way junctions for the proper tubular network of the endoplasmic reticulum

2019 ◽  
Vol 476 (21) ◽  
pp. 3241-3260
Author(s):  
Sindhu Wisesa ◽  
Yasunori Yamamoto ◽  
Toshiaki Sakisaka
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Proteins ◽  
Membrane Protein ◽  
Mammalian Cells ◽  
Coiled Coil ◽  
Transmembrane Domains ◽  
Domain Family ◽  
Coiled Coil Domain ◽  
U2os Cells ◽  
Er Membrane

The tubular network of the endoplasmic reticulum (ER) is formed by connecting ER tubules through three-way junctions. Two classes of the conserved ER membrane proteins, atlastins and lunapark, have been shown to reside at the three-way junctions so far and be involved in the generation and stabilization of the three-way junctions. In this study, we report TMCC3 (transmembrane and coiled-coil domain family 3), a member of the TEX28 family, as another ER membrane protein that resides at the three-way junctions in mammalian cells. When the TEX28 family members were transfected into U2OS cells, TMCC3 specifically localized at the three-way junctions in the peripheral ER. TMCC3 bound to atlastins through the C-terminal transmembrane domains. A TMCC3 mutant lacking the N-terminal coiled-coil domain abolished localization to the three-way junctions, suggesting that TMCC3 localized independently of binding to atlastins. TMCC3 knockdown caused a decrease in the number of three-way junctions and expansion of ER sheets, leading to a reduction of the tubular ER network in U2OS cells. The TMCC3 knockdown phenotype was partially rescued by the overexpression of atlastin-2, suggesting that TMCC3 knockdown would decrease the activity of atlastins. These results indicate that TMCC3 localizes at the three-way junctions for the proper tubular ER network.

Spatial localization of unknown proteins in the endoplasmic reticulum predicts functions

2007 ◽  
Vol 30 (4) ◽  
pp. 84
Author(s):  
Michael D. Jain ◽  
Hisao Nagaya ◽  
Annalyn Gilchrist ◽  
Miroslaw Cygler ◽  
John J.M. Bergeron
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Folding ◽  
Protein Synthesis ◽  
Protein Function ◽  
Protein Translocation ◽  
Spatial Localization ◽  
Predict Protein Function ◽  
Insight Into ◽  
Soluble Fractions ◽  
Er Membrane

Protein synthesis, folding and degradation functions are spatially segregated in the endoplasmic reticulum (ER) with respect to the membrane and the ribosome (rough and smooth ER). Interrogation of a proteomics resource characterizing rough and smooth ER membranes subfractionated into cytosolic, membrane, and soluble fractions gives a spatial map of known proteins involved in ER function. The spatial localization of 224 identified unknown proteins in the ER is predicted to give insight into their function. Here we provide evidence that the proteomics resource accurately predicts the function of new proteins involved in protein synthesis (nudilin), protein translocation across the ER membrane (nicalin), co-translational protein folding (stexin), and distal protein folding in the lumen of the ER (erlin-1, TMX2). Proteomics provides the spatial localization of proteins and can be used to accurately predict protein function.

scholarly journals Efficient MHC Class I-Independent Amino-Terminal Trimming of Epitope Precursor Peptides in the Endoplasmic Reticulum

Immunity ◽  
2001 ◽  
Vol 15 (3) ◽  
pp. 467-476 ◽  
Author(s):  
Doriana Fruci ◽  
Gabriele Niedermann ◽  
Richard H Butler ◽  
Peter M van Endert
Keyword(s):  
Endoplasmic Reticulum ◽  
Mhc Class I ◽  
Class I ◽  
Amino Terminal
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