51
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Abstract
At least 150 human proteins are glycosylphosphatidylinositol-anchored proteins (GPI-APs). The protein moiety of GPI-APs lacking transmembrane domains is anchored to the plasma membrane with GPI covalently attached to the C-terminus. The GPI consists of the conserved core glycan, phosphatidylinositol and glycan side chains. The entire GPI-AP is anchored to the outer leaflet of the lipid bilayer by insertion of fatty chains of phosphatidylinositol. Because of GPI-dependent membrane anchoring, GPI-APs have some unique characteristics. The most prominent feature of GPI-APs is their association with membrane microdomains or membrane rafts. In the polarized cells such as epithelial cells, many GPI-APs are exclusively expressed in the apical surfaces, whereas some GPI-APs are preferentially expressed in the basolateral surfaces. Several GPI-APs act as transcytotic transporters carrying their ligands from one compartment to another. Some GPI-APs are shed from the membrane after cleavage within the GPI by a GPI-specific phospholipase or a glycosidase. In this review, I will summarize the current understanding of GPI-AP biosynthesis in mammalian cells and discuss examples of GPI-dependent functions of mammalian GPI-APs.
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Affiliation(s)
- Taroh Kinoshita
- Yabumoto Department of Intractable Disease Research, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka, Japan
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52
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Abstract
The past several decades have witnessed tremendous growth in the protein targeting, transport and translocation field. Major advances were made during this time period. Now the molecular details of the targeting factors, receptors and the membrane channels that were envisioned in Blobel's Signal Hypothesis in the 1970s have been revealed by powerful structural methods. It is evident that there is a myriad of cytosolic and membrane associated systems that accurately sort and target newly synthesized proteins to their correct membrane translocases for membrane insertion or protein translocation. Here we will describe the common principles for protein transport in prokaryotes and eukaryotes.
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53
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Lakshminarayan R, Phillips BP, Binnian IL, Gomez-Navarro N, Escudero-Urquijo N, Warren AJ, Miller EA. Pre-emptive Quality Control of a Misfolded Membrane Protein by Ribosome-Driven Effects. Curr Biol 2020; 30:854-864.e5. [PMID: 31956032 PMCID: PMC7063571 DOI: 10.1016/j.cub.2019.12.060] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Revised: 12/02/2019] [Accepted: 12/19/2019] [Indexed: 12/13/2022]
Abstract
Cells possess multiple mechanisms that protect against the accumulation of toxic aggregation-prone proteins. Here, we identify a pre-emptive pathway that reduces synthesis of membrane proteins that have failed to properly assemble in the endoplasmic reticulum (ER). We show that loss of the ER membrane complex (EMC) or mutation of the Sec61 translocon causes reduced synthesis of misfolded forms of the yeast ABC transporter Yor1. Synthesis defects are rescued by various ribosomal mutations, as well as by reducing cellular ribosome abundance. Genetic and biochemical evidence point to a ribosome-associated quality-control pathway triggered by ribosome collisions when membrane domain insertion and/or folding fails. In support of this model, translation initiation also contributes to synthesis defects, likely by modulating ribosome abundance on the message. Examination of translation efficiency across the yeast membrane proteome revealed that polytopic membrane proteins have relatively low ribosome abundance, providing evidence for translational tuning to balance protein synthesis and folding. We propose that by modulating translation rates of poorly folded proteins, cells can pre-emptively protect themselves from potentially toxic aberrant transmembrane proteins. Yor1-ΔF shows synthesis defects when Sec61 or EMC function is compromised Synthesis defects are suppressed by ribosomal and RQC mutants Translation initiation is a second point of potential regulation Pre-emptive quality control on the ER might protect the cell from aberrant proteins
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Affiliation(s)
- Ramya Lakshminarayan
- Department of Biological Sciences, Columbia University, 1212 Amsterdam Ave., New York, NY 10027, USA
| | - Ben P Phillips
- Medical Research Council Laboratory of Molecular Biology, Cambridge Biomedical Campus, Francis Crick Ave., Cambridge CB2 0QH, UK
| | - Imogen L Binnian
- Medical Research Council Laboratory of Molecular Biology, Cambridge Biomedical Campus, Francis Crick Ave., Cambridge CB2 0QH, UK
| | - Natalia Gomez-Navarro
- Medical Research Council Laboratory of Molecular Biology, Cambridge Biomedical Campus, Francis Crick Ave., Cambridge CB2 0QH, UK
| | - Norberto Escudero-Urquijo
- Cambridge Institute for Medical Research, The Keith Peters Building, University of Cambridge, Hills Road, Cambridge CB2 0XY, UK; Department of Haematology, The Keith Peters Building, University of Cambridge, Hills Road, Cambridge CB2 0XY, UK; Wellcome Trust - Medical Research Council Stem Cell Institute, University of Cambridge, Puddicomb Way, Cambridge CB2 0AW, UK
| | - Alan J Warren
- Cambridge Institute for Medical Research, The Keith Peters Building, University of Cambridge, Hills Road, Cambridge CB2 0XY, UK; Department of Haematology, The Keith Peters Building, University of Cambridge, Hills Road, Cambridge CB2 0XY, UK; Wellcome Trust - Medical Research Council Stem Cell Institute, University of Cambridge, Puddicomb Way, Cambridge CB2 0AW, UK
| | - Elizabeth A Miller
- Department of Biological Sciences, Columbia University, 1212 Amsterdam Ave., New York, NY 10027, USA; Medical Research Council Laboratory of Molecular Biology, Cambridge Biomedical Campus, Francis Crick Ave., Cambridge CB2 0QH, UK.
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54
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Castells-Ballester J, Rinis N, Kotan I, Gal L, Bausewein D, Kats I, Zatorska E, Kramer G, Bukau B, Schuldiner M, Strahl S. Translational Regulation of Pmt1 and Pmt2 by Bfr1 Affects Unfolded Protein O-Mannosylation. Int J Mol Sci 2019; 20:ijms20246220. [PMID: 31835530 PMCID: PMC6940804 DOI: 10.3390/ijms20246220] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 12/05/2019] [Accepted: 12/06/2019] [Indexed: 12/15/2022] Open
Abstract
O-mannosylation is implicated in protein quality control in Saccharomyces cerevisiae due to the attachment of mannose to serine and threonine residues of un- or misfolded proteins in the endoplasmic reticulum (ER). This process also designated as unfolded protein O-mannosylation (UPOM) that ends futile folding cycles and saves cellular resources is mainly mediated by protein O-mannosyltransferases Pmt1 and Pmt2. Here we describe a genetic screen for factors that influence O-mannosylation in yeast, using slow-folding green fluorescent protein (GFP) as a reporter. Our screening identifies the RNA binding protein brefeldin A resistance factor 1 (Bfr1) that has not been linked to O-mannosylation and ER protein quality control before. We find that Bfr1 affects O-mannosylation through changes in Pmt1 and Pmt2 protein abundance but has no effect on PMT1 and PMT2 transcript levels, mRNA localization to the ER membrane or protein stability. Ribosome profiling reveals that Bfr1 is a crucial factor for Pmt1 and Pmt2 translation thereby affecting unfolded protein O-mannosylation. Our results uncover a new level of regulation of protein quality control in the secretory pathway.
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Affiliation(s)
- Joan Castells-Ballester
- Centre for Organismal Studies (COS), Glycobiology, Heidelberg University, D-69120 Heidelberg, Germany; (J.C.-B.); (N.R.); (D.B.); (E.Z.)
| | - Natalie Rinis
- Centre for Organismal Studies (COS), Glycobiology, Heidelberg University, D-69120 Heidelberg, Germany; (J.C.-B.); (N.R.); (D.B.); (E.Z.)
| | - Ilgin Kotan
- Center for Molecular Biology of Heidelberg University (ZMBH), German Cancer Research Center (DKFZ), ZMBH-DKFZ Alliance, D-69120 Heidelberg, Germany; (I.K.); (I.K.); (G.K.); (B.B.)
| | - Lihi Gal
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel; (L.G.); (M.S.)
| | - Daniela Bausewein
- Centre for Organismal Studies (COS), Glycobiology, Heidelberg University, D-69120 Heidelberg, Germany; (J.C.-B.); (N.R.); (D.B.); (E.Z.)
- spm—Safety Projects & More GmbH, D-69493 Hirschberg a. d. Bergstraße, Germany
| | - Ilia Kats
- Center for Molecular Biology of Heidelberg University (ZMBH), German Cancer Research Center (DKFZ), ZMBH-DKFZ Alliance, D-69120 Heidelberg, Germany; (I.K.); (I.K.); (G.K.); (B.B.)
| | - Ewa Zatorska
- Centre for Organismal Studies (COS), Glycobiology, Heidelberg University, D-69120 Heidelberg, Germany; (J.C.-B.); (N.R.); (D.B.); (E.Z.)
| | - Günter Kramer
- Center for Molecular Biology of Heidelberg University (ZMBH), German Cancer Research Center (DKFZ), ZMBH-DKFZ Alliance, D-69120 Heidelberg, Germany; (I.K.); (I.K.); (G.K.); (B.B.)
| | - Bernd Bukau
- Center for Molecular Biology of Heidelberg University (ZMBH), German Cancer Research Center (DKFZ), ZMBH-DKFZ Alliance, D-69120 Heidelberg, Germany; (I.K.); (I.K.); (G.K.); (B.B.)
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel; (L.G.); (M.S.)
| | - Sabine Strahl
- Centre for Organismal Studies (COS), Glycobiology, Heidelberg University, D-69120 Heidelberg, Germany; (J.C.-B.); (N.R.); (D.B.); (E.Z.)
- Correspondence: ; Tel.: +49-6221-54-6286
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55
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Abstract
One-fourth of eukaryotic genes code for integral membrane proteins, nearly all of which are inserted and assembled at the endoplasmic reticulum (ER). The defining feature of membrane proteins is one or more transmembrane domains (TMDs). During membrane protein biogenesis, TMDs are selectively recognized, shielded, and chaperoned into the lipid bilayer, where they often assemble with other TMDs. If maturation fails, exposed TMDs serve as a cue for engagement of degradation pathways. Thus, TMD-recognition factors in the cytosol and ER are essential for membrane protein biogenesis and quality control. Here, we discuss the growing assortment of cytosolic and membrane-embedded TMD-recognition factors, the pathways within which they operate, and mechanistic principles of recognition.
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56
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Wang S, Jomaa A, Jaskolowski M, Yang CI, Ban N, Shan SO. The molecular mechanism of cotranslational membrane protein recognition and targeting by SecA. Nat Struct Mol Biol 2019; 26:919-929. [PMID: 31570874 PMCID: PMC6858539 DOI: 10.1038/s41594-019-0297-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2019] [Accepted: 08/12/2019] [Indexed: 11/16/2022]
Abstract
Cotranslational protein targeting is a conserved process for membrane protein biogenesis. In Escherichia coli, the essential ATPase SecA was found to cotranslationally target a subset of nascent membrane proteins to the SecYEG translocase at the plasma membrane. The molecular mechanism of this pathway remains unclear. Here we use biochemical and cryoelectron microscopy analyses to show that the amino-terminal amphipathic helix of SecA and the ribosomal protein uL23 form a composite binding site for the transmembrane domain (TMD) on the nascent protein. This binding mode further enables recognition of charged residues flanking the nascent TMD and thus explains the specificity of SecA recognition. Finally, we show that membrane-embedded SecYEG promotes handover of the translating ribosome from SecA to the translocase via a concerted mechanism. Our work provides a molecular description of the SecA-mediated cotranslational targeting pathway and demonstrates an unprecedented role of the ribosome in shielding nascent TMDs.
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Affiliation(s)
- Shuai Wang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Ahmad Jomaa
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, Zurich, Switzerland
| | - Mateusz Jaskolowski
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, Zurich, Switzerland
| | - Chien-I Yang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Nenad Ban
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, Zurich, Switzerland.
| | - Shu-Ou Shan
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA.
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57
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Spatial transcriptome profiling by MERFISH reveals subcellular RNA compartmentalization and cell cycle-dependent gene expression. Proc Natl Acad Sci U S A 2019; 116:19490-19499. [PMID: 31501331 PMCID: PMC6765259 DOI: 10.1073/pnas.1912459116] [Citation(s) in RCA: 359] [Impact Index Per Article: 71.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
The spatial organization of RNAs within cells and spatial patterning of cells within tissues play crucial roles in many biological processes. Here, we demonstrate that multiplexed error-robust FISH (MERFISH) can achieve near-genome-wide, spatially resolved RNA profiling of individual cells with high accuracy and high detection efficiency. Using this approach, we identified RNA species enriched in different subcellular compartments, observed transcriptionally distinct cell states corresponding to different cell-cycle phases, and revealed spatial patterning of transcriptionally distinct cells. Spatially resolved transcriptome quantification within cells further enabled RNA velocity and pseudotime analysis, which revealed numerous genes with cell cycle-dependent expression. We anticipate that spatially resolved transcriptome analysis will advance our understanding of the interplay between gene regulation and spatial context in biological systems. The expression profiles and spatial distributions of RNAs regulate many cellular functions. Image-based transcriptomic approaches provide powerful means to measure both expression and spatial information of RNAs in individual cells within their native environment. Among these approaches, multiplexed error-robust fluorescence in situ hybridization (MERFISH) has achieved spatially resolved RNA quantification at transcriptome scale by massively multiplexing single-molecule FISH measurements. Here, we increased the gene throughput of MERFISH and demonstrated simultaneous measurements of RNA transcripts from ∼10,000 genes in individual cells with ∼80% detection efficiency and ∼4% misidentification rate. We combined MERFISH with cellular structure imaging to determine subcellular compartmentalization of RNAs. We validated this approach by showing enrichment of secretome transcripts at the endoplasmic reticulum, and further revealed enrichment of long noncoding RNAs, RNAs with retained introns, and a subgroup of protein-coding mRNAs in the cell nucleus. Leveraging spatially resolved RNA profiling, we developed an approach to determine RNA velocity in situ using the balance of nuclear versus cytoplasmic RNA counts. We applied this approach to infer pseudotime ordering of cells and identified cells at different cell-cycle states, revealing ∼1,600 genes with putative cell cycle-dependent expression and a gradual transcription profile change as cells progress through cell-cycle stages. Our analysis further revealed cell cycle-dependent and cell cycle-independent spatial heterogeneity of transcriptionally distinct cells. We envision that the ability to perform spatially resolved, genome-wide RNA profiling with high detection efficiency and accuracy by MERFISH could help address a wide array of questions ranging from the regulation of gene expression in cells to the development of cell fate and organization in tissues.
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58
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Proper insertion and topogenesis of membrane proteins in the ER depend on Sec63. Biochim Biophys Acta Gen Subj 2019; 1863:1371-1380. [DOI: 10.1016/j.bbagen.2019.06.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Revised: 05/28/2019] [Accepted: 06/04/2019] [Indexed: 11/30/2022]
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59
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Wild K, Becker MM, Kempf G, Sinning I. Structure, dynamics and interactions of large SRP variants. Biol Chem 2019; 401:63-80. [DOI: 10.1515/hsz-2019-0282] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2019] [Accepted: 08/09/2019] [Indexed: 12/11/2022]
Abstract
Abstract
Co-translational protein targeting to membranes relies on the signal recognition particle (SRP) system consisting of a cytosolic ribonucleoprotein complex and its membrane-associated receptor. SRP recognizes N-terminal cleavable signals or signal anchor sequences, retards translation, and delivers ribosome-nascent chain complexes (RNCs) to vacant translocation channels in the target membrane. While our mechanistic understanding is well advanced for the small bacterial systems it lags behind for the large bacterial, archaeal and eukaryotic SRP variants including an Alu and an S domain. Here we describe recent advances on structural and functional insights in domain architecture, particle dynamics and interplay with RNCs and translocon and GTP-dependent regulation of co-translational protein targeting stimulated by SRP RNA.
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Affiliation(s)
- Klemens Wild
- Heidelberg University Biochemistry Center (BZH) , INF 328 , D-69120 Heidelberg , Germany
| | - Matthias M.M. Becker
- Heidelberg University Biochemistry Center (BZH) , INF 328 , D-69120 Heidelberg , Germany
| | - Georg Kempf
- Heidelberg University Biochemistry Center (BZH) , INF 328 , D-69120 Heidelberg , Germany
| | - Irmgard Sinning
- Heidelberg University Biochemistry Center (BZH) , INF 328 , D-69120 Heidelberg , Germany
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60
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Cohen-Zontag O, Baez C, Lim LQJ, Olender T, Schirman D, Dahary D, Pilpel Y, Gerst JE. A secretion-enhancing cis regulatory targeting element (SECReTE) involved in mRNA localization and protein synthesis. PLoS Genet 2019; 15:e1008248. [PMID: 31260446 PMCID: PMC6625729 DOI: 10.1371/journal.pgen.1008248] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Revised: 07/12/2019] [Accepted: 06/13/2019] [Indexed: 12/19/2022] Open
Abstract
The localization of mRNAs encoding secreted/membrane proteins (mSMPs) to the endoplasmic reticulum (ER) likely facilitates the co-translational translocation of secreted proteins. However, studies have shown that mSMP recruitment to the ER in eukaryotes can occur in a manner that is independent of the ribosome, translational control, and the signal recognition particle, although the mechanism remains largely unknown. Here, we identify a cis-acting RNA sequence motif that enhances mSMP localization to the ER and appears to increase mRNA stability, and both the synthesis and secretion of secretome proteins. Termed SECReTE, for secretion-enhancing cis regulatory targeting element, this motif is enriched in mRNAs encoding secretome proteins translated on the ER in eukaryotes and on the inner membrane of prokaryotes. SECReTE consists of ≥10 nucleotide triplet repeats enriched with pyrimidine (C/U) every third base (i.e. NNY, where N = any nucleotide, Y = pyrimidine) and can be present in the untranslated as well as the coding regions of the mRNA. Synonymous mutations that elevate the SECReTE count in a given mRNA (e.g. SUC2, HSP150, and CCW12) lead to an increase in protein secretion in yeast, while a reduction in count led to less secretion and physiological defects. Moreover, the addition of SECReTE to the 3'UTR of an mRNA for an exogenously expressed protein (e.g. GFP) led to its increased secretion from yeast cells. Thus, SECReTE constitutes a novel RNA motif that facilitates ER-localized mRNA translation and protein secretion.
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Affiliation(s)
- Osnat Cohen-Zontag
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Camila Baez
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Lisha Qiu Jin Lim
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Tsviya Olender
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Dvir Schirman
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Dvir Dahary
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Yitzhak Pilpel
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Jeffrey E. Gerst
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
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61
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Chen L, Geng X, Ma Y, Zhao J, Chen W, Xing X, Shi Y, Sun B, Li H. The ER Lumenal Hsp70 Protein FpLhs1 Is Important for Conidiation and Plant Infection in Fusarium pseudograminearum. Front Microbiol 2019; 10:1401. [PMID: 31316483 PMCID: PMC6611370 DOI: 10.3389/fmicb.2019.01401] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Accepted: 06/04/2019] [Indexed: 11/19/2022] Open
Abstract
Heat shock protein 70s (Hsp70s) are a class of molecular chaperones that are highly conserved and ubiquitous in organisms ranging from microorganisms to plants and humans. Hsp70s play key roles in cellular development and protecting living organisms from environmental stresses such as heat, drought, salinity, acidity, and cold. However, their functions in pathogenic fungi are largely unknown. Here, a total of 14 FpHsp70 genes were identified in Fusarium pseudograminearum, including 3 in the mitochondria, 7 in the cytoplasm, 2 in the endoplasmic reticulum (ER), 1 in the nucleus, and 1 in the plastid. However, the exon–intron boundaries and protein motifs of the FpHsp70 have no consistency in the same subfamily. Expression analysis revealed that most FpHsp70 genes were up-regulated during infection, implying that FpHsp70 genes may play important roles in F. pseudograminearum pathogenicity. Furthermore, knockout of an ER lumenal Hsp70 homolog FpLhs1 gene reduced growth, conidiation, and pathogenicity in F. pseudograminearum. These mutants also showed a defect in secretion of some proteins. Together, FpHsp70s might play essential roles in F. pseudograminearum and FpLhs1 is likely to act on the development and virulence by regulating protein secretion.
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Affiliation(s)
- Linlin Chen
- College of Plant Protection, Henan Agricultural University, Zhengzhou, China.,National Key Laboratory of Wheat and Maize Crop Science, Zhengzhou, China
| | - Xuejing Geng
- College of Plant Protection, Henan Agricultural University, Zhengzhou, China
| | - Yuming Ma
- College of Plant Protection, Henan Agricultural University, Zhengzhou, China
| | - Jingya Zhao
- College of Plant Protection, Henan Agricultural University, Zhengzhou, China
| | - Wenbo Chen
- College of Plant Protection, Henan Agricultural University, Zhengzhou, China
| | - Xiaoping Xing
- College of Plant Protection, Henan Agricultural University, Zhengzhou, China
| | - Yan Shi
- College of Plant Protection, Henan Agricultural University, Zhengzhou, China
| | - Bingjian Sun
- College of Plant Protection, Henan Agricultural University, Zhengzhou, China
| | - Honglian Li
- College of Plant Protection, Henan Agricultural University, Zhengzhou, China.,National Key Laboratory of Wheat and Maize Crop Science, Zhengzhou, China
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62
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Three J-proteins impact Hsp104-mediated variant-specific prion elimination: a new critical role for a low-complexity domain. Curr Genet 2019; 66:51-58. [PMID: 31230108 PMCID: PMC6925661 DOI: 10.1007/s00294-019-01006-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Revised: 06/12/2019] [Accepted: 06/13/2019] [Indexed: 12/13/2022]
Abstract
Prions are self-propagating protein isoforms that are typically amyloid. In Saccharomyces cerevisiae, amyloid prion aggregates are fragmented by a trio involving three classes of chaperone proteins: Hsp40s, also known as J-proteins, Hsp70s, and Hsp104. Hsp104, the sole Hsp100-class disaggregase in yeast, along with the Hsp70 Ssa and the J-protein Sis1, is required for the propagation of all known amyloid yeast prions. However, when Hsp104 is ectopically overexpressed, only the prion [PSI+] is efficiently eliminated from cell populations via a highly debated mechanism that also requires Sis1. Recently, we reported roles for two additional J-proteins, Apj1 and Ydj1, in this process. Deletion of Apj1, a J-protein involved in the degradation of sumoylated proteins, partially blocks Hsp104-mediated [PSI+] elimination. Apj1 and Sis1 were found to have overlapping functions, as overexpression of one compensates for loss of function of the other. In addition, overexpression of Ydj1, the most abundant J-protein in the yeast cytosol, completely blocks Hsp104-mediated curing. Yeast prions exhibit structural polymorphisms known as “variants”; most intriguingly, these J-protein effects were only observed for strong variants, suggesting variant-specific mechanisms. Here, we review these results and present new data resolving the domains of Apj1 responsible, specifically implicating the involvement of Apj1’s Q/S-rich low-complexity domain.
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63
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Kramer G, Shiber A, Bukau B. Mechanisms of Cotranslational Maturation of Newly Synthesized Proteins. Annu Rev Biochem 2019; 88:337-364. [DOI: 10.1146/annurev-biochem-013118-111717] [Citation(s) in RCA: 98] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The timely production of functional proteins is of critical importance for the biological activity of cells. To reach the functional state, newly synthesized polypeptides have to become enzymatically processed, folded, and assembled into oligomeric complexes and, for noncytosolic proteins, translocated across membranes. Key activities of these processes occur cotranslationally, assisted by a network of machineries that transiently engage nascent polypeptides at distinct phases of translation. The sequence of events is tuned by intrinsic features of the nascent polypeptides and timely association of factors with the translating ribosome. Considering the dynamics of translation, the heterogeneity of cellular proteins, and the diversity of interaction partners, it is a major cellular achievement that these processes are temporally and spatially so precisely coordinated, minimizing the generation of damaged proteins. This review summarizes the current progress we have made toward a comprehensive understanding of the cotranslational interactions of nascent chains, which pave the way to their functional state.
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Affiliation(s)
- Günter Kramer
- Center for Molecular Biology of Heidelberg University (ZMBH) and German Cancer Research Center (DKFZ), DKFZ-ZMBH Alliance, D-69120 Heidelberg, Germany;,
| | - Ayala Shiber
- Center for Molecular Biology of Heidelberg University (ZMBH) and German Cancer Research Center (DKFZ), DKFZ-ZMBH Alliance, D-69120 Heidelberg, Germany;,
| | - Bernd Bukau
- Center for Molecular Biology of Heidelberg University (ZMBH) and German Cancer Research Center (DKFZ), DKFZ-ZMBH Alliance, D-69120 Heidelberg, Germany;,
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64
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Campos RK, Garcia-Blanco MA, Bradrick SS. Roles of Pro-viral Host Factors in Mosquito-Borne Flavivirus Infections. Curr Top Microbiol Immunol 2019; 419:43-67. [PMID: 28688087 DOI: 10.1007/82_2017_26] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Identification and analysis of viral host factors is a growing area of research which aims to understand the how viruses molecularly interface with the host cell. Investigations into flavivirus-host interactions has led to new discoveries in viral and cell biology, and will potentially bolster strategies to control the important diseases caused by these pathogens. Here, we address the current knowledge of prominent host factors required for the flavivirus life-cycle and mechanisms by which they promote infection.
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Affiliation(s)
- Rafael K Campos
- Department of Molecular Genetics and Microbiology, Center for RNA Biology, Duke University, Durham, NC, USA.,Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, USA
| | - Mariano A Garcia-Blanco
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, USA. .,Programme in Emerging Infectious Diseases, Duke-NUS Medical School, Singapore, Singapore.
| | - Shelton S Bradrick
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, USA.
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65
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Elia F, Yadhanapudi L, Tretter T, Römisch K. The N-terminus of Sec61p plays key roles in ER protein import and ERAD. PLoS One 2019; 14:e0215950. [PMID: 31017954 PMCID: PMC6481919 DOI: 10.1371/journal.pone.0215950] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Accepted: 04/11/2019] [Indexed: 01/24/2023] Open
Abstract
Sec61p is the channel-forming subunit of the heterotrimeric Sec61 complex that mediates co-translational protein import into the endoplasmic reticulum (ER). In yeast, proteins can also be post-translationally translocated by the hetero-heptameric Sec complex, composed of the Sec61 and the Sec63 complexes. The Sec61 channel is also a candidate for the dislocation channel for misfolded proteins from the ER to the cytosol during ER-associated degradation (ERAD). The structure of the Sec61 complex is highly conserved, but the roles of its N-terminal acetylation and its amphipathic N-terminal helix are unknown so far. To gain insight into the function of the Sec61p N-terminus, we mutated its N-acetylation site, deleted its amphipathic helix, or both the helix and the N-acetylation site. Mutation of the N-acetylation site on its own had no effect on protein import into the ER in intact cells, but resulted in an ERAD defect. Yeast expressing sec61 without the N-terminal amphipathic helix displayed severe growth defects and had profound defects in post-translational protein import into the ER. Nevertheless the formation of the hetero-heptameric Sec complex was not affected. Instead, the lack of the N-terminal amphipathic helix compromised the integrity of the heterotrimeric Sec61 complex. We conclude that the N-terminal helix of Sec61p is required for post-translational protein import into the ER and Sec61 complex stability, whereas N-terminal acetylation of Sec61p plays a role in ERAD.
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Affiliation(s)
- Francesco Elia
- Faculty of Natural Sciences and Technology, Saarland University, Saarbruecken, Germany
| | - Lalitha Yadhanapudi
- Faculty of Natural Sciences and Technology, Saarland University, Saarbruecken, Germany
| | - Thomas Tretter
- Faculty of Natural Sciences and Technology, Saarland University, Saarbruecken, Germany
| | - Karin Römisch
- Faculty of Natural Sciences and Technology, Saarland University, Saarbruecken, Germany
- * E-mail:
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The exonuclease Xrn1 activates transcription and translation of mRNAs encoding membrane proteins. Nat Commun 2019; 10:1298. [PMID: 30899024 PMCID: PMC6428865 DOI: 10.1038/s41467-019-09199-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2018] [Accepted: 02/26/2019] [Indexed: 12/11/2022] Open
Abstract
The highly conserved 5’–3’ exonuclease Xrn1 regulates gene expression in eukaryotes by coupling nuclear DNA transcription to cytosolic mRNA decay. By integrating transcriptome-wide analyses of translation with biochemical and functional studies, we demonstrate an unanticipated regulatory role of Xrn1 in protein synthesis. Xrn1 promotes translation of a specific group of transcripts encoding membrane proteins. Xrn1-dependence for translation is linked to poor structural RNA contexts for translation initiation, is mediated by interactions with components of the translation initiation machinery and correlates with an Xrn1-dependence for mRNA localization at the endoplasmic reticulum, the translation compartment of membrane proteins. Importantly, for this group of mRNAs, Xrn1 stimulates transcription, mRNA translation and decay. Our results uncover a crosstalk between the three major stages of gene expression coordinated by Xrn1 to maintain appropriate levels of membrane proteins. The exonuclease Xrn1 mediates crosstalk between transcription and mRNA decay in yeast. Here the authors demonstrate that Xrn1 promotes translation of mRNAs encoding membrane proteins, coupling transcription, translation, and mRNA decay.
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Ziska A, Tatzelt J, Dudek J, Paton AW, Paton JC, Zimmermann R, Haßdenteufel S. The signal peptide plus a cluster of positive charges in prion protein dictate chaperone-mediated Sec61 channel gating. Biol Open 2019; 8:bio.040691. [PMID: 30745438 PMCID: PMC6451349 DOI: 10.1242/bio.040691] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The Sec61-complex as a dynamic polypeptide-conducting channel mediates protein transport into the human endoplasmic reticulum (ER) with the help of additional components. ER membrane resident Hsp40-type co-chaperone Sec63 as well as the ER lumenal Hsp70-type chaperone BiP were proposed to facilitate channel opening in a precursor-specific fashion. Here, we report on their rules of engagement in ER import of the prion protein (PrP) by addressing sixteen PrP-related variants which differ in their signal peptides and mature parts, respectively. Transport into the ER of semi-permeabilized human cells was analyzed upon depletion of the components by siRNA- or toxin-treatment. The results are consistent with the view of separate functions of BiP and Sec63 and strongly suggest that the co-chaperone/chaperone-pair facilitates Sec61 channel gating to the open state when precursor polypeptides with weak signal peptides in combination with detrimental features in the adjacent mature part were targeted. Thus, we expand the view of chaperone-mediated Sec61 channel gating by providing a novel example of a polybasic motif that interferes with signal peptide-mediated Sec61 channel gating. This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Anke Ziska
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Jörg Tatzelt
- Department Biochemistry of Neurodegenerative Diseases, Institute of Biochemistry and Pathobiochemistry, Ruhr University, 44801 Bochum, Germany
| | - Johanna Dudek
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Adrienne W Paton
- School of Molecular and Biomedical Sciences, Research Centre for Infectious Disease, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - James C Paton
- School of Molecular and Biomedical Sciences, Research Centre for Infectious Disease, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Richard Zimmermann
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Sarah Haßdenteufel
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
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Benarroch R, Austin JM, Ahmed F, Isaacson RL. The roles of cytosolic quality control proteins, SGTA and the BAG6 complex, in disease. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2019; 114:265-313. [PMID: 30635083 PMCID: PMC7102839 DOI: 10.1016/bs.apcsb.2018.11.002] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
SGTA is a co-chaperone that, in collaboration with the complex of BAG6/UBL4A/TRC35, facilitates the biogenesis and quality control of hydrophobic proteins, protecting them from the aqueous cytosolic environment. This work includes targeting tail-anchored proteins to their resident membranes, sorting of membrane and secretory proteins that mislocalize to the cytoplasm and endoplasmic reticulum-associated degradation of misfolded proteins. Since these functions are all vital for the cell's continued proteostasis, their disruption poses a threat to the cell, with a particular risk of protein aggregation, a phenomenon that underpins many diseases. Although the specific disease implications of machinery involved in quality control of hydrophobic substrates are poorly understood, here we summarize much of the available information on this topic.
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Affiliation(s)
- Rashi Benarroch
- Department of Chemistry, King's College London, London, United Kingdom
| | - Jennifer M Austin
- Department of Chemistry, King's College London, London, United Kingdom
| | - Fahmeda Ahmed
- Department of Chemistry, King's College London, London, United Kingdom
| | - Rivka L Isaacson
- Department of Chemistry, King's College London, London, United Kingdom.
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Lang S, Nguyen D, Pfeffer S, Förster F, Helms V, Zimmermann R. Functions and Mechanisms of the Human Ribosome-Translocon Complex. Subcell Biochem 2019; 93:83-141. [PMID: 31939150 DOI: 10.1007/978-3-030-28151-9_4] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The membrane of the endoplasmic reticulum (ER) in human cells harbors the protein translocon, which facilitates membrane insertion and translocation of almost every newly synthesized polypeptide targeted to organelles of the secretory pathway. The translocon comprises the polypeptide-conducting Sec61 channel and several additional proteins, which are associated with the heterotrimeric Sec61 complex. This ensemble of proteins facilitates ER targeting of precursor polypeptides, Sec61 channel opening and closing, and modification of precursor polypeptides in transit through the Sec61 complex. Recently, cryoelectron tomography of translocons in native ER membranes has given unprecedented insights into the architecture and dynamics of the native, ribosome-associated translocon and the Sec61 channel. These structural data are discussed in light of different Sec61 channel activities including ribosome receptor function, membrane insertion or translocation of newly synthesized polypeptides as well as the possible roles of the Sec61 channel as a passive ER calcium leak channel and regulator of ATP/ADP exchange between cytosol and ER.
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Affiliation(s)
- Sven Lang
- Competence Center for Molecular Medicine, Saarland University Medical School, Building 44, 66421, Homburg, Germany.
| | - Duy Nguyen
- Center for Bioinformatics, Saarland University, 66041, Saarbrücken, Germany
| | - Stefan Pfeffer
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, 82152, Martinsried, Germany
- ZMBH, 69120, Heidelberg, Germany
| | - Friedrich Förster
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, 82152, Martinsried, Germany
- Center for Biomolecular Research, Utrecht University, 3584 CH, Utrecht, The Netherlands
| | - Volkhard Helms
- Center for Bioinformatics, Saarland University, 66041, Saarbrücken, Germany
| | - Richard Zimmermann
- Competence Center for Molecular Medicine, Saarland University Medical School, Building 44, 66421, Homburg, Germany
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Structure of the post-translational protein translocation machinery of the ER membrane. Nature 2018; 566:136-139. [PMID: 30644436 PMCID: PMC6367035 DOI: 10.1038/s41586-018-0856-x] [Citation(s) in RCA: 81] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2018] [Accepted: 12/18/2018] [Indexed: 11/09/2022]
Abstract
Many proteins must translocate through the protein-conducting Sec61 channel in the eukaryotic endoplasmic reticulum membrane or the SecY channel in the prokaryotic plasma membrane1,2. Proteins with highly hydrophobic signal sequences are first recognized by the signal recognition particle (SRP)3,4 and then moved co-translationally through the Sec61 or SecY channel by the associated translating ribosome. Substrates with less hydrophobic signal sequences bypass the SRP and are moved through the channel post-translationally5,6. In eukaryotic cells, post-translational translocation is mediated by the association of the Sec61 channel with another membrane protein complex, the Sec62-Sec63 complex7-9, and substrates are moved through the channel by the luminal BiP ATPase9. How the Sec62-Sec63 complex activates the Sec61 channel for post-translational translocation is not known. Here we report the electron cryo-microscopy structure of the Sec complex from Saccharomyces cerevisiae, 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 Hsp7010. Our structure shows how the Sec61 channel is activated for post-translational protein translocation.
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Abstract
Budding yeast is an excellent model organism for studying the dynamics of the Golgi apparatus. To characterize Golgi function, it is important to visualize secretory cargo as it traverses the secretory pathway. We describe a recently developed approach that generates fluorescent protein aggregates in the lumen of the yeast endoplasmic reticulum and allows the fluorescent cargo to be solubilized for transport through the Golgi by addition of a small-molecule ligand. We further describe how to generate a yeast strain expressing the regulatable secretory cargo, and we provide protocols for visualizing the cargo by 4D confocal microscopy and immunoblotting. © 2018 by John Wiley & Sons, Inc.
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Affiliation(s)
- Jason C Casler
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois
| | - Benjamin S Glick
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois
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Yim C, Jung SJ, Kim JEH, Jung Y, Jeong SD, Kim H. Profiling of signal sequence characteristics and requirement of different translocation components. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2018; 1865:1640-1648. [DOI: 10.1016/j.bbamcr.2018.08.018] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Revised: 08/23/2018] [Accepted: 08/27/2018] [Indexed: 11/25/2022]
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Castells-Ballester J, Zatorska E, Meurer M, Neubert P, Metschies A, Knop M, Strahl S. Monitoring Protein Dynamics in Protein O-Mannosyltransferase Mutants In Vivo by Tandem Fluorescent Protein Timers. Molecules 2018; 23:E2622. [PMID: 30322079 PMCID: PMC6222916 DOI: 10.3390/molecules23102622] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Revised: 10/05/2018] [Accepted: 10/09/2018] [Indexed: 12/27/2022] Open
Abstract
For proteins entering the secretory pathway, a major factor contributing to maturation and homeostasis is glycosylation. One relevant type of protein glycosylation is O-mannosylation, which is essential and evolutionarily-conserved in fungi, animals, and humans. Our recent proteome-wide study in the eukaryotic model organism Saccharomyces cerevisiae revealed that more than 26% of all proteins entering the secretory pathway receive O-mannosyl glycans. In a first attempt to understand the impact of O-mannosylation on these proteins, we took advantage of a tandem fluorescent timer (tFT) reporter to monitor different aspects of protein dynamics. We analyzed tFT-reporter fusions of 137 unique O-mannosylated proteins, mainly of the secretory pathway and the plasma membrane, in mutants lacking the major protein O-mannosyltransferases Pmt1, Pmt2, or Pmt4. In these three pmtΔ mutants, a total of 39 individual proteins were clearly affected, and Pmt-specific substrate proteins could be identified. We observed that O-mannosylation may cause both enhanced and diminished protein abundance and/or stability when compromised, and verified our findings on the examples of Axl2-tFT and Kre6-tFT fusion proteins. The identified target proteins are a valuable resource towards unraveling the multiple functions of O-mannosylation at the molecular level.
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Affiliation(s)
| | - Ewa Zatorska
- Centre for Organismal Studies (COS), Heidelberg University, 69120 Heidelberg, Germany.
| | - Matthias Meurer
- Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), DKFZ-ZMBH Alliance, Heidelberg University, 69120 Heidelberg, Germany.
| | - Patrick Neubert
- Centre for Organismal Studies (COS), Heidelberg University, 69120 Heidelberg, Germany.
| | - Anke Metschies
- Centre for Organismal Studies (COS), Heidelberg University, 69120 Heidelberg, Germany.
| | - Michael Knop
- Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), DKFZ-ZMBH Alliance, Heidelberg University, 69120 Heidelberg, Germany.
- Deutsches Krebsforschungszentrum (DKFZ), DKFZ-ZMBH Alliance, 69120 Heidelberg, Germany.
| | - Sabine Strahl
- Centre for Organismal Studies (COS), Heidelberg University, 69120 Heidelberg, Germany.
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Barrero JJ, Casler JC, Valero F, Ferrer P, Glick BS. An improved secretion signal enhances the secretion of model proteins from Pichia pastoris. Microb Cell Fact 2018; 17:161. [PMID: 30314480 PMCID: PMC6182871 DOI: 10.1186/s12934-018-1009-5] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Accepted: 10/08/2018] [Indexed: 12/16/2022] Open
Abstract
Background Proteins can be secreted from a host organism with the aid of N-terminal secretion signals. The budding yeast Pichia pastoris (Komagataella sp.) is widely employed to secrete proteins of academic and industrial interest. For this yeast, the most commonly used secretion signal is the N-terminal portion of pre-pro-α-factor from Saccharomyces cerevisiae. However, this secretion signal promotes posttranslational translocation into the endoplasmic reticulum (ER), so proteins that can fold in the cytosol may be inefficiently translocated and thus poorly secreted. In addition, if a protein self-associates, the α-factor pro region can potentially cause aggregation, thereby hampering export from the ER. This study addresses both limitations of the pre-pro-α-factor secretion signal. Results We engineered a hybrid secretion signal consisting of the S. cerevisiae Ost1 signal sequence, which promotes cotranslational translocation into the ER, followed by the α-factor pro region. Secretion and intracellular localization were assessed using as a model protein the tetrameric red fluorescent protein E2-Crimson. When paired with the α-factor pro region, the Ost1 signal sequence yielded much more efficient secretion than the α-factor signal sequence. Moreover, an allelic variant of the α-factor pro region reduced aggregation of the E2-Crimson construct in the ER. The resulting improved secretion signal enhanced secretion of E2-Crimson up to 20-fold compared to the levels obtained with the original α-factor secretion signal. Similar findings were obtained with the lipase BTL2, which exhibited 10-fold enhanced secretion with the improved secretion signal. Conclusions The improved secretion signal confers dramatic benefits for the secretion of certain proteins from P. pastoris. These benefits are likely to be most evident for proteins that can fold in the cytosol and for oligomeric proteins. Electronic supplementary material The online version of this article (10.1186/s12934-018-1009-5) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Juan J Barrero
- Department of Chemical, Biological and Environmental Engineering, Escola d'Enginyeria, Universitat Autònoma de Barcelona, Bellaterra (Cerdanyola del Vallès), 08193, Catalonia, Spain.,Department of Molecular Genetics and Cell Biology, University of Chicago, 920 East 58th Street, Chicago, IL, 60637, USA
| | - Jason C Casler
- Department of Molecular Genetics and Cell Biology, University of Chicago, 920 East 58th Street, Chicago, IL, 60637, USA
| | - Francisco Valero
- Department of Chemical, Biological and Environmental Engineering, Escola d'Enginyeria, Universitat Autònoma de Barcelona, Bellaterra (Cerdanyola del Vallès), 08193, Catalonia, Spain
| | - Pau Ferrer
- Department of Chemical, Biological and Environmental Engineering, Escola d'Enginyeria, Universitat Autònoma de Barcelona, Bellaterra (Cerdanyola del Vallès), 08193, Catalonia, Spain.,Luxembourg Institute of Science and Technology (LIST), Belvaux, Luxembourg
| | - Benjamin S Glick
- Department of Molecular Genetics and Cell Biology, University of Chicago, 920 East 58th Street, Chicago, IL, 60637, USA.
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Aviram N, Schuldiner M. Targeting and translocation of proteins to the endoplasmic reticulum at a glance. J Cell Sci 2018; 130:4079-4085. [PMID: 29246967 DOI: 10.1242/jcs.204396] [Citation(s) in RCA: 86] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The evolutionary emergence of organelles was a defining process in diversifying biochemical reactions within the cell and enabling multicellularity. However, compartmentalization also imposed a great challenge-the need to import proteins synthesized in the cytosol into their respective sites of function. For example, one-third of all genes encode for proteins that must be targeted and translocated into the endoplasmic reticulum (ER), which serves as the entry site to the majority of endomembrane compartments. Decades of research have set down the fundamental principles of how proteins get from the cytosol into the ER, and recent studies have brought forward new pathways and additional regulators enabling better definition of the rules governing substrate recognition. In this Cell Science at a Glance article and the accompanying poster, we give an overview of our current understanding of the multifaceted and regulated processes of protein targeting and translocation to the ER.
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Affiliation(s)
- Naama Aviram
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel 7610001
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel 7610001
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76
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Mandon EC, Butova C, Lachapelle A, Gilmore R. Conserved motifs on the cytoplasmic face of the protein translocation channel are critical for the transition between resting and active conformations. J Biol Chem 2018; 293:13662-13672. [PMID: 29986881 DOI: 10.1074/jbc.ra118.004123] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2018] [Revised: 06/26/2018] [Indexed: 11/06/2022] Open
Abstract
The Sec61 complex is the primary cotranslational protein translocation channel in yeast (Saccharomyces cerevisiae). The structural transition between the closed inactive conformation of the Sec61 complex and its open and active conformation is thought to be promoted by binding of the ribosome nascent-chain complex to the cytoplasmic surface of the Sec61 complex. Here, we have analyzed new yeast Sec61 mutants that selectively interfere with cotranslational translocation across the endoplasmic reticulum. We found that a single substitution at the junction between transmembrane segment TM7 and the L6/7 loop interferes with cotranslational translocation by uncoupling ribosome binding to the L6/7 loop from the separation of the lateral gate transmembrane spans. Substitutions replacing basic residues with acidic residues in the C-terminal tail of Sec61 had an unanticipated impact upon binding of ribosomes to the Sec61 complex. We found that similar charge-reversal mutations in the N-terminal tail and in cytoplasmic loop L2/3 did not alter ribosome binding but interfered with translocation channel gating. These findings indicated that these segments are important for the structural transition between the inactive and active conformations of the Sec61 complex. In summary our results have identified additional cytosolic segments of the Sec61 complex important for promoting the structural transition between the closed and open conformations of the complex. We conclude that positively charged residues in multiple cytosolic segments, as well as bulky hydrophobic residues in the L6/7-TM7 junction, are required for cotranslational translocation or integration of membrane proteins by the Sec61 complex.
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Affiliation(s)
- Elisabet C Mandon
- From the Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605
| | - Cameron Butova
- From the Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605
| | - Amber Lachapelle
- From the Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605
| | - Reid Gilmore
- From the Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605
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Van Puyenbroeck V, Vermeire K. Inhibitors of protein translocation across membranes of the secretory pathway: novel antimicrobial and anticancer agents. Cell Mol Life Sci 2018; 75:1541-1558. [PMID: 29305616 PMCID: PMC5897483 DOI: 10.1007/s00018-017-2743-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2017] [Revised: 12/15/2017] [Accepted: 12/27/2017] [Indexed: 12/22/2022]
Abstract
Proteins routed to the secretory pathway start their journey by being transported across biological membranes, such as the endoplasmic reticulum. The essential nature of this protein translocation process has led to the evolution of several factors that specifically target the translocon and block translocation. In this review, various translocation pathways are discussed together with known inhibitors of translocation. Properties of signal peptide-specific systems are highlighted for the development of new therapeutic and antimicrobial applications, as compounds can target signal peptides from either host cells or pathogens and thereby selectively prevent translocation of those specific proteins. Broad inhibition of translocation is also an interesting target for the development of new anticancer drugs because cancer cells heavily depend on efficient protein translocation into the endoplasmic reticulum to support their fast growth.
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Affiliation(s)
- Victor Van Puyenbroeck
- Laboratory of Virology and Chemotherapy, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven - University of Leuven, 3000, Leuven, Belgium
| | - Kurt Vermeire
- Laboratory of Virology and Chemotherapy, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven - University of Leuven, 3000, Leuven, Belgium.
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Tsirigotaki A, Chatzi KE, Koukaki M, De Geyter J, Portaliou AG, Orfanoudaki G, Sardis MF, Trelle MB, Jørgensen TJD, Karamanou S, Economou A. Long-Lived Folding Intermediates Predominate the Targeting-Competent Secretome. Structure 2018; 26:695-707.e5. [PMID: 29606594 DOI: 10.1016/j.str.2018.03.006] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Revised: 02/02/2018] [Accepted: 03/08/2018] [Indexed: 10/17/2022]
Abstract
Secretory preproteins carry signal peptides fused amino-terminally to mature domains. They are post-translationally targeted to cross the plasma membrane in non-folded states with the help of translocases, and fold only at their final destinations. The mechanism of this process of postponed folding is unknown, but is generally attributed to signal peptides and chaperones. We herein demonstrate that, during targeting, most mature domains maintain loosely packed folding intermediates. These largely soluble states are signal peptide independent and essential for translocase recognition. These intermediates are promoted by mature domain features: residue composition, elevated disorder, and reduced hydrophobicity. Consequently, a mature domain folds slower than its cytoplasmic structural homolog. Some mature domains could not evolve stable, loose intermediates, and hence depend on signal peptides for slow folding to the detriment of solubility. These unique features of secretory proteins impact our understanding of protein trafficking, folding, and aggregation, and thus place them in a distinct class.
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Affiliation(s)
- Alexandra Tsirigotaki
- KU Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, 3000 Leuven, Belgium
| | - Katerina E Chatzi
- KU Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, 3000 Leuven, Belgium
| | - Marina Koukaki
- Institute of Molecular Biology and Biotechnology, FoRTH, University of Crete, 70013 Heraklion, Crete, Greece
| | - Jozefien De Geyter
- KU Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, 3000 Leuven, Belgium
| | - Athina G Portaliou
- KU Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, 3000 Leuven, Belgium
| | - Georgia Orfanoudaki
- Institute of Molecular Biology and Biotechnology, FoRTH, University of Crete, 70013 Heraklion, Crete, Greece
| | - Marios Frantzeskos Sardis
- KU Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, 3000 Leuven, Belgium
| | - Morten Beck Trelle
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, 5230 Odense M, Denmark
| | - Thomas J D Jørgensen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, 5230 Odense M, Denmark
| | - Spyridoula Karamanou
- KU Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, 3000 Leuven, Belgium
| | - Anastassios Economou
- KU Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, 3000 Leuven, Belgium.
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Costa EA, Subramanian K, Nunnari J, Weissman JS. Defining the physiological role of SRP in protein-targeting efficiency and specificity. Science 2018; 359:689-692. [PMID: 29348368 PMCID: PMC5970945 DOI: 10.1126/science.aar3607] [Citation(s) in RCA: 144] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Accepted: 01/04/2018] [Indexed: 01/03/2023]
Abstract
The signal recognition particle (SRP) enables cotranslational delivery of proteins for translocation into the endoplasmic reticulum (ER), but its full in vivo role remains incompletely explored. We combined rapid auxin-induced SRP degradation with proximity-specific ribosome profiling to define SRP's in vivo function in yeast. Despite the classic view that SRP recognizes amino-terminal signal sequences, we show that SRP was generally essential for targeting transmembrane domains regardless of their position relative to the amino terminus. By contrast, many proteins containing cleavable amino-terminal signal peptides were efficiently cotranslationally targeted in SRP's absence. We also reveal an unanticipated consequence of SRP loss: Transcripts normally targeted to the ER were mistargeted to mitochondria, leading to mitochondrial defects. These results elucidate SRP's essential roles in maintaining the efficiency and specificity of protein targeting.
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Affiliation(s)
- Elizabeth A Costa
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA, USA
| | - Kelly Subramanian
- Department of Molecular and Cellular Biology, University of California, Davis, CA, USA
| | - Jodi Nunnari
- Department of Molecular and Cellular Biology, University of California, Davis, CA, USA
| | - Jonathan S Weissman
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA, USA.
- Howard Hughes Medical Institute, University of California, San Francisco, CA, USA
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80
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Abstract
Efficient movement of proteins across membranes is required for cell health. The translocation process is particularly challenging when the channel in the membrane through which proteins must pass is narrow—such as those in the membranes of the endoplasmic reticulum and mitochondria. Hsp70 molecular chaperones play roles on both sides of these membranes, ensuring efficient translocation of proteins synthesized on cytosolic ribosomes into the interior of these organelles. The “import motor” in the mitochondrial matrix, which is essential for driving the movement of proteins across the mitochondrial inner membrane, is arguably the most complex Hsp70-based system in the cell.
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Affiliation(s)
- Elizabeth A Craig
- Department of Biochemistry, University of Wisconsin - Madison, 433 Babcock Drive, Madison, WI, 53706, USA.
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81
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Guo H, Sun J, Li X, Xiong Y, Wang H, Shu H, Zhu R, Liu Q, Huang Y, Madley R, Wang Y, Cui J, Arvan P, Liu M. Positive charge in the n-region of the signal peptide contributes to efficient post-translational translocation of small secretory preproteins. J Biol Chem 2017; 293:1899-1907. [PMID: 29229776 DOI: 10.1074/jbc.ra117.000922] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Revised: 11/30/2017] [Indexed: 12/17/2022] Open
Abstract
Increasing evidence indicates that many small secretory preproteins can undergo post-translational translocation across the membrane of the endoplasmic reticulum. Although the cellular machinery involved in post-translational translocation of small secretory preproteins has begun to be elucidated, the intrinsic signals contained within these small secretory preproteins that contribute to their efficient post-translational translocation remain unknown. Here, we analyzed the eukaryotic secretory proteome and discovered the small secretory preproteins tend to have a higher probability to harbor the positive charge in the n-region of the signal peptide (SP). Eliminating the positive charge of the n-region blocked post-translational translocation of newly synthesized preproteins and selectively impaired translocation efficiency of small secretory preproteins. The pathophysiological significance of the positive charge in the n-region of SP was underscored by recently identified preproinsulin SP mutations that impair translocation of preproinsulin and cause maturity onset diabetes of youth (MODY). Remarkably, we have found that slowing the polypeptide elongation rate of small secretory preproteins could alleviate the translocation defect caused by loss of the n-region positive charge of the signal peptide. Together, these data reveal not only a previously unrecognized role of the n-region's positive charge in ensuring efficient post-translational translocation of small secretory preproteins, but they also highlight the molecular contribution of defects in this process to the pathogenesis of genetic disorders such as MODY.
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Affiliation(s)
- Huan Guo
- From the Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, Tianjin 300052, China.,the Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105, and
| | - Jinhong Sun
- From the Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, Tianjin 300052, China.,the Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105, and
| | - Xin Li
- From the Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, Tianjin 300052, China
| | - Yi Xiong
- the Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105, and
| | - Heting Wang
- From the Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, Tianjin 300052, China
| | - Hua Shu
- From the Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, Tianjin 300052, China
| | - Ruimin Zhu
- From the Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, Tianjin 300052, China
| | - Qi Liu
- From the Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, Tianjin 300052, China
| | - Yumeng Huang
- From the Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, Tianjin 300052, China
| | - Rachel Madley
- the Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105, and
| | - Yulun Wang
- the Division of Endocrinology, Tianjin People's Hospital, Tianjin 300120, China
| | - Jingqiu Cui
- From the Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, Tianjin 300052, China
| | - Peter Arvan
- the Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105, and
| | - Ming Liu
- From the Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, Tianjin 300052, China, .,the Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105, and
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82
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Eisenberg-Bord M, Mari M, Weill U, Rosenfeld-Gur E, Moldavski O, Castro IG, Soni KG, Harpaz N, Levine TP, Futerman AH, Reggiori F, Bankaitis VA, Schuldiner M, Bohnert M. Identification of seipin-linked factors that act as determinants of a lipid droplet subpopulation. J Cell Biol 2017; 217:269-282. [PMID: 29187527 PMCID: PMC5748981 DOI: 10.1083/jcb.201704122] [Citation(s) in RCA: 86] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2017] [Revised: 09/21/2017] [Accepted: 10/23/2017] [Indexed: 02/07/2023] Open
Abstract
Eisenberg-Bord et al. describe a lipid droplet (LD) subpopulation with a unique proteome, which is adjacent to the nucleus–vacuole junction contact site. They identify the LD machinery, which cooperates with the lipodystrophy factor seipin as a key determinant of LD identity and suggest a mechanism for functional organelle diversification. Functional heterogeneity within the lipid droplet (LD) pool of a single cell has been observed, yet the underlying mechanisms remain enigmatic. Here, we report on identification of a specialized LD subpopulation characterized by a unique proteome and a defined geographical location at the nucleus–vacuole junction contact site. In search for factors determining identity of these LDs, we screened ∼6,000 yeast mutants for loss of targeting of the subpopulation marker Pdr16 and identified Ldo45 (LD organization protein of 45 kD) as a crucial targeting determinant. Ldo45 is the product of a splicing event connecting two adjacent genes (YMR147W and YMR148W/OSW5/LDO16). We show that Ldo proteins cooperate with the LD biogenesis component seipin and establish LD identity by defining positioning and surface-protein composition. Our studies suggest a mechanism to establish functional differentiation of organelles, opening the door to better understanding of metabolic decisions in cells.
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Affiliation(s)
| | - Muriel Mari
- Department of Cell Biology, University of Groningen, University Medical Center Groningen, Groningen, Netherlands
| | - Uri Weill
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Eden Rosenfeld-Gur
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Ofer Moldavski
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Inês G Castro
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Krishnakant G Soni
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, TX
| | - Nofar Harpaz
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Tim P Levine
- UCL Institute of Ophthalmology, London, England, UK
| | - Anthony H Futerman
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Fulvio Reggiori
- Department of Cell Biology, University of Groningen, University Medical Center Groningen, Groningen, Netherlands
| | - Vytas A Bankaitis
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, TX
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Maria Bohnert
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
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83
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Lang S, Pfeffer S, Lee PH, Cavalié A, Helms V, Förster F, Zimmermann R. An Update on Sec61 Channel Functions, Mechanisms, and Related Diseases. Front Physiol 2017; 8:887. [PMID: 29163222 PMCID: PMC5672155 DOI: 10.3389/fphys.2017.00887] [Citation(s) in RCA: 95] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2017] [Accepted: 10/19/2017] [Indexed: 12/18/2022] Open
Abstract
The membrane of the endoplasmic reticulum (ER) of nucleated human cells harbors the protein translocon, which facilitates membrane integration or translocation of almost every newly synthesized polypeptide targeted to organelles of the endo- and exocytotic pathway. The translocon comprises the polypeptide-conducting Sec61 channel and several additional proteins and complexes that are permanently or transiently associated with the heterotrimeric Sec61 complex. This ensemble of proteins facilitates ER targeting of precursor polypeptides, modification of precursor polypeptides in transit through the Sec61 complex, and Sec61 channel gating, i.e., dynamic regulation of the pore forming subunit to mediate precursor transport and calcium efflux. Recently, cryoelectron tomography of translocons in native ER membrane vesicles, derived from human cell lines or patient fibroblasts, and even intact cells has given unprecedented insights into the architecture and dynamics of the native translocon and the Sec61 channel. These structural data are discussed in light of different Sec61 channel activities including ribosome receptor function, membrane insertion, and translocation of newly synthesized polypeptides as well as the putative physiological roles of the Sec61 channel as a passive ER calcium leak channel. Furthermore, the structural insights into the Sec61 channel are incorporated into an overview and update on Sec61 channel-related diseases—the Sec61 channelopathies—and novel therapeutic concepts for their treatment.
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Affiliation(s)
- Sven Lang
- Competence Center for Molecular Medicine, Saarland University Medical School, Homburg, Germany
| | - Stefan Pfeffer
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, Martinsried, Germany
| | - Po-Hsien Lee
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Adolfo Cavalié
- Experimental and Clinical Pharmacology and Toxicology, Saarland University, Homburg, Germany
| | - Volkhard Helms
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Friedrich Förster
- Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht, Netherlands
| | - Richard Zimmermann
- Competence Center for Molecular Medicine, Saarland University Medical School, Homburg, Germany
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84
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Wang S, Yang CI, Shan SO. SecA mediates cotranslational targeting and translocation of an inner membrane protein. J Cell Biol 2017; 216:3639-3653. [PMID: 28928132 PMCID: PMC5674894 DOI: 10.1083/jcb.201704036] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2017] [Revised: 07/17/2017] [Accepted: 08/02/2017] [Indexed: 12/02/2022] Open
Abstract
Proteins are thought to be delivered to the bacterial plasma membrane cotranslationally by signal recognition particle or posttranslationally by SecA. Wang et al. identify a new membrane protein–targeting pathway in bacteria in which SecA cotranslationally recognizes and targets the inner membrane protein RodZ, which harbors an internal transmembrane domain. Protein targeting to the bacterial plasma membrane was generally thought to occur via two major pathways: cotranslational targeting by signal recognition particle (SRP) and posttranslational targeting by SecA and SecB. Recently, SecA was found to also bind ribosomes near the nascent polypeptide exit tunnel, but the function of this SecA–ribosome contact remains unclear. In this study, we show that SecA cotranslationally recognizes the nascent chain of an inner membrane protein, RodZ, with high affinity and specificity. In vitro reconstitution and in vivo targeting assays show that SecA is necessary and sufficient to direct the targeting and translocation of RodZ to the bacterial plasma membrane in an obligatorily cotranslational mechanism. Sequence elements upstream and downstream of the RodZ transmembrane domain dictate nascent polypeptide selection by SecA instead of the SRP machinery. These findings identify a new route for the targeting of inner membrane proteins in bacteria and highlight the diversity of targeting pathways that enables an organism to accommodate diverse nascent proteins.
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Affiliation(s)
- Shuai Wang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA
| | - Chien-I Yang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA
| | - Shu-Ou Shan
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA
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85
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Haßdenteufel S, Sicking M, Schorr S, Aviram N, Fecher-Trost C, Schuldiner M, Jung M, Zimmermann R, Lang S. hSnd2 protein represents an alternative targeting factor to the endoplasmic reticulum in human cells. FEBS Lett 2017; 591:3211-3224. [PMID: 28862756 DOI: 10.1002/1873-3468.12831] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Revised: 08/22/2017] [Accepted: 08/24/2017] [Indexed: 12/11/2022]
Abstract
Recently, understanding of protein targeting to the endoplasmic reticulum (ER) was expanded by the discovery of multiple pathways that function in parallel to the signal recognition particle (SRP). Guided entry of tail-anchored proteins and SRP independent (SND) are two such targeting pathways described in yeast. So far, no human SND component is functionally characterized. Here, we report hSnd2 as the first constituent of the human SND pathway able to support substrate-specific protein targeting to the ER. Similar to its yeast counterpart, hSnd2 is assumed to function as a membrane-bound receptor preferentially targeting precursors carrying C-terminal transmembrane domains. Our genetic and physical interaction studies show that hSnd2 is part of a complex network of targeting and translocation that is dynamically regulated.
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Affiliation(s)
- Sarah Haßdenteufel
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Mark Sicking
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Stefan Schorr
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Naama Aviram
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Claudia Fecher-Trost
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Saarland University, Homburg, Germany
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Martin Jung
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Richard Zimmermann
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Sven Lang
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
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86
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Geva Y, Crissman J, Arakel EC, Gómez-Navarro N, Chuartzman SG, Stahmer KR, Schwappach B, Miller EA, Schuldiner M. Two novel effectors of trafficking and maturation of the yeast plasma membrane H + -ATPase. Traffic 2017; 18:672-682. [PMID: 28727280 PMCID: PMC5607100 DOI: 10.1111/tra.12503] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Revised: 07/17/2017] [Accepted: 07/17/2017] [Indexed: 11/28/2022]
Abstract
The endoplasmic reticulum (ER) is the entry site of proteins into the endomembrane system. Proteins exit the ER via coat protein II (COPII) vesicles in a selective manner, mediated either by direct interaction with the COPII coat or aided by cargo receptors. Despite the fundamental role of such receptors in protein sorting, only a few have been identified. To further define the machinery that packages secretory cargo and targets proteins from the ER to Golgi membranes, we used multiple systematic approaches, which revealed 2 uncharacterized proteins that mediate the trafficking and maturation of Pma1, the essential yeast plasma membrane proton ATPase. Ydl121c (Exp1) is an ER protein that binds Pma1, is packaged into COPII vesicles, and whose deletion causes ER retention of Pma1. Ykl077w (Psg1) physically interacts with Exp1 and can be found in the Golgi and coat protein I (COPI) vesicles but does not directly bind Pma1. Loss of Psg1 causes enhanced degradation of Pma1 in the vacuole. Our findings suggest that Exp1 is a Pma1 cargo receptor and that Psg1 aids Pma1 maturation in the Golgi or affects its retrieval. More generally our work shows the utility of high content screens in the identification of novel trafficking components.
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Affiliation(s)
- Yosef Geva
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Jonathan Crissman
- Department of Biological Sciences, Columbia University, New York, NY
| | - Eric C Arakel
- Department of Molecular Biology, Universitätsmedizin Göttingen, Göttingen, Germany
| | | | - Silvia G Chuartzman
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Kyle R Stahmer
- Department of Biological Sciences, Columbia University, New York, NY
| | - Blanche Schwappach
- Department of Molecular Biology, Universitätsmedizin Göttingen, Göttingen, Germany
| | - Elizabeth A Miller
- Department of Biological Sciences, Columbia University, New York, NY.,MRC Laboratory of Molecular Biology, Cell Biology Division, Cambridge, UK
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
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87
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Döring K, Ahmed N, Riemer T, Suresh HG, Vainshtein Y, Habich M, Riemer J, Mayer MP, O'Brien EP, Kramer G, Bukau B. Profiling Ssb-Nascent Chain Interactions Reveals Principles of Hsp70-Assisted Folding. Cell 2017; 170:298-311.e20. [PMID: 28708998 DOI: 10.1016/j.cell.2017.06.038] [Citation(s) in RCA: 106] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Revised: 04/04/2017] [Accepted: 06/23/2017] [Indexed: 12/21/2022]
Abstract
The yeast Hsp70 chaperone Ssb interacts with ribosomes and nascent polypeptides to assist protein folding. To reveal its working principle, we determined the nascent chain-binding pattern of Ssb at near-residue resolution by in vivo selective ribosome profiling. Ssb associates broadly with cytosolic, nuclear, and hitherto unknown substrate classes of mitochondrial and endoplasmic reticulum (ER) nascent proteins, supporting its general chaperone function. Ssb engages most substrates by multiple binding-release cycles to a degenerate sequence enriched in positively charged and aromatic amino acids. Timely association with this motif upon emergence at the ribosomal tunnel exit requires ribosome-associated complex (RAC) but not nascent polypeptide-associated complex (NAC). Ribosome footprint densities along orfs reveal faster translation at times of Ssb binding, mainly imposed by biases in mRNA secondary structure, codon usage, and Ssb action. Ssb thus employs substrate-tailored dynamic nascent chain associations to coordinate co-translational protein folding, facilitate accelerated translation, and support membrane targeting of organellar proteins.
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Affiliation(s)
- Kristina Döring
- Center for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, Heidelberg, Germany; German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg, Germany
| | - Nabeel Ahmed
- Bioinformatics and Genomics Graduate Program, The Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA, USA
| | - Trine Riemer
- Center for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, Heidelberg, Germany; German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg, Germany
| | - Harsha Garadi Suresh
- Center for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, Heidelberg, Germany; German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg, Germany; The Donnelly Centre, University of Toronto, 160 College Street, Toronto ON, Canada
| | - Yevhen Vainshtein
- Center for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, Heidelberg, Germany
| | - Markus Habich
- Institute of Biochemistry, University of Cologne, Zuelpicher Str. 47, Cologne, Germany
| | - Jan Riemer
- Institute of Biochemistry, University of Cologne, Zuelpicher Str. 47, Cologne, Germany
| | - Matthias P Mayer
- Center for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, Heidelberg, Germany
| | - Edward P O'Brien
- Bioinformatics and Genomics Graduate Program, The Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA, USA; Department of Chemistry, Pennsylvania State University, University Park, PA, USA
| | - Günter Kramer
- Center for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, Heidelberg, Germany; German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg, Germany.
| | - Bernd Bukau
- Center for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, Heidelberg, Germany; German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg, Germany.
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88
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Abstract
Many proteins are translocated across the endoplasmic reticulum (ER) membrane in eukaryotes or the plasma membrane in prokaryotes. These proteins use hydrophobic signal sequences or transmembrane (TM) segments to trigger their translocation through the protein-conducting Sec61/SecY channel. Substrates are first directed to the channel by cytosolic targeting factors, which use hydrophobic pockets to bind diverse signal and TM sequences. Subsequently, these hydrophobic sequences insert into the channel, docking into a groove on the outside of the lateral gate of the channel, where they also interact with lipids. Structural data and biochemical experiments have elucidated how channel partners, the ribosome in cotranslational translocation, and the eukaryotic ER chaperone BiP or the prokaryotic cytosolic SecA ATPase in posttranslational translocation move polypeptides unidirectionally across the membrane. Structures of auxiliary components of the bacterial translocon, YidC and SecD/F, provide additional insight. Taken together, these recent advances result in mechanistic models of protein translocation.
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Affiliation(s)
- Tom A Rapoport
- Department of Cell Biology, Howard Hughes Medical Institute and Harvard Medical School, Boston, Massachusetts 02115; ,
| | - Long Li
- Department of Cell Biology, Howard Hughes Medical Institute and Harvard Medical School, Boston, Massachusetts 02115; ,
| | - Eunyong Park
- The Rockefeller University and Howard Hughes Medical Institute, New York, NY 10065;
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89
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Aviram N, Ast T, Costa EA, Arakel EC, Chuartzman SG, Jan CH, Haßdenteufel S, Dudek J, Jung M, Schorr S, Zimmermann R, Schwappach B, Weissman JS, Schuldiner M. The SND proteins constitute an alternative targeting route to the endoplasmic reticulum. Nature 2017; 540:134-138. [PMID: 27905431 DOI: 10.1038/nature20169] [Citation(s) in RCA: 147] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2016] [Accepted: 10/18/2016] [Indexed: 12/19/2022]
Abstract
In eukaryotes, up to one-third of cellular proteins are targeted to the endoplasmic reticulum, where they undergo folding, processing, sorting and trafficking to subsequent endomembrane compartments. Targeting to the endoplasmic reticulum has been shown to occur co-translationally by the signal recognition particle (SRP) pathway or post-translationally by the mammalian transmembrane recognition complex of 40 kDa (TRC40) and homologous yeast guided entry of tail-anchored proteins (GET) pathways. Despite the range of proteins that can be catered for by these two pathways, many proteins are still known to be independent of both SRP and GET, so there seems to be a critical need for an additional dedicated pathway for endoplasmic reticulum relay. We set out to uncover additional targeting proteins using unbiased high-content screening approaches. To this end, we performed a systematic visual screen using the yeast Saccharomyces cerevisiae, and uncovered three uncharacterized proteins whose loss affected targeting. We suggest that these proteins work together and demonstrate that they function in parallel with SRP and GET to target a broad range of substrates to the endoplasmic reticulum. The three proteins, which we name Snd1, Snd2 and Snd3 (for SRP-independent targeting), can synthetically compensate for the loss of both the SRP and GET pathways, and act as a backup targeting system. This explains why it has previously been difficult to demonstrate complete loss of targeting for some substrates. Our discovery thus puts in place an essential piece of the endoplasmic reticulum targeting puzzle, highlighting how the targeting apparatus of the eukaryotic cell is robust, interlinked and flexible.
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Affiliation(s)
- Naama Aviram
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Tslil Ast
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Elizabeth A Costa
- Department of Cellular and Molecular Pharmacology, UCSF California Institute for Quantitative Biomedical Research and Howard Hughes Medical Institute, San Francisco, California 94158-2330, USA
| | - Eric C Arakel
- Department of Molecular Biology, University Medical Center Göttingen, 37073 Göttingen, Germany
| | - Silvia G Chuartzman
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Calvin H Jan
- Department of Cellular and Molecular Pharmacology, UCSF California Institute for Quantitative Biomedical Research and Howard Hughes Medical Institute, San Francisco, California 94158-2330, USA
| | - Sarah Haßdenteufel
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Johanna Dudek
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Martin Jung
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Stefan Schorr
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Richard Zimmermann
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Blanche Schwappach
- Department of Molecular Biology, University Medical Center Göttingen, 37073 Göttingen, Germany.,Max-Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Jonathan S Weissman
- Department of Cellular and Molecular Pharmacology, UCSF California Institute for Quantitative Biomedical Research and Howard Hughes Medical Institute, San Francisco, California 94158-2330, USA
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
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90
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Tripathi A, Mandon EC, Gilmore R, Rapoport TA. Two alternative binding mechanisms connect the protein translocation Sec71-Sec72 complex with heat shock proteins. J Biol Chem 2017; 292:8007-8018. [PMID: 28286332 DOI: 10.1074/jbc.m116.761122] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Revised: 03/09/2017] [Indexed: 12/20/2022] Open
Abstract
The biosynthesis of many eukaryotic proteins requires accurate targeting to and translocation across the endoplasmic reticulum membrane. Post-translational protein translocation in yeast requires both the Sec61 translocation channel, and a complex of four additional proteins: Sec63, Sec62, Sec71, and Sec72. The structure and function of these proteins are largely unknown. This pathway also requires the cytosolic Hsp70 protein Ssa1, but whether Ssa1 associates with the translocation machinery to target protein substrates to the membrane is unclear. Here, we use a combined structural and biochemical approach to explore the role of Sec71-Sec72 subcomplex in post-translational protein translocation. To this end, we report a crystal structure of the Sec71-Sec72 complex, which revealed that Sec72 contains a tetratricopeptide repeat (TPR) domain that is anchored to the endoplasmic reticulum membrane by Sec71. We also determined the crystal structure of this TPR domain with a C-terminal peptide derived from Ssa1, which suggests how Sec72 interacts with full-length Ssa1. Surprisingly, Ssb1, a cytoplasmic Hsp70 that binds ribosome-associated nascent polypeptide chains, also binds to the TPR domain of Sec72, even though it lacks the TPR-binding C-terminal residues of Ssa1. We demonstrate that Ssb1 binds through its ATPase domain to the TPR domain, an interaction that leads to inhibition of nucleotide exchange. Taken together, our results suggest that translocation substrates can be recruited to the Sec71-Sec72 complex either post-translationally through Ssa1 or co-translationally through Ssb1.
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Affiliation(s)
- Arati Tripathi
- From the Howard Hughes Medical Institute and the Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115 and
| | - Elisabet C Mandon
- the Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605
| | - Reid Gilmore
- the Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605
| | - Tom A Rapoport
- From the Howard Hughes Medical Institute and the Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115 and
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91
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Rivera-Monroy J, Musiol L, Unthan-Fechner K, Farkas Á, Clancy A, Coy-Vergara J, Weill U, Gockel S, Lin SY, Corey DP, Kohl T, Ströbel P, Schuldiner M, Schwappach B, Vilardi F. Mice lacking WRB reveal differential biogenesis requirements of tail-anchored proteins in vivo. Sci Rep 2016; 6:39464. [PMID: 28000760 PMCID: PMC5175141 DOI: 10.1038/srep39464] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Accepted: 11/22/2016] [Indexed: 02/06/2023] Open
Abstract
Tail-anchored (TA) proteins are post-translationally inserted into membranes. The TRC40 pathway targets TA proteins to the endoplasmic reticulum via a receptor comprised of WRB and CAML. TRC40 pathway clients have been identified using in vitro assays, however, the relevance of the TRC40 pathway in vivo remains unknown. We followed the fate of TA proteins in two tissue-specific WRB knockout mouse models and found that their dependence on the TRC40 pathway in vitro did not predict their reaction to receptor depletion in vivo. The SNARE syntaxin 5 (Stx5) was extremely sensitive to disruption of the TRC40 pathway. Screening yeast TA proteins with mammalian homologues, we show that the particular sensitivity of Stx5 is conserved, possibly due to aggregation propensity of its cytoplasmic domain. We establish that Stx5 is an autophagy target that is inefficiently membrane-targeted by alternative pathways. Our results highlight an intimate relationship between the TRC40 pathway and cellular proteostasis.
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Affiliation(s)
- Jhon Rivera-Monroy
- Department of Molecular Biology, Universitätsmedizin Göttingen, D-37073 Göttingen, Germany
| | - Lena Musiol
- Department of Molecular Biology, Universitätsmedizin Göttingen, D-37073 Göttingen, Germany
| | - Kirsten Unthan-Fechner
- Department of Molecular Biology, Universitätsmedizin Göttingen, D-37073 Göttingen, Germany
| | - Ákos Farkas
- Department of Molecular Biology, Universitätsmedizin Göttingen, D-37073 Göttingen, Germany
| | - Anne Clancy
- Department of Molecular Biology, Universitätsmedizin Göttingen, D-37073 Göttingen, Germany
| | - Javier Coy-Vergara
- Department of Molecular Biology, Universitätsmedizin Göttingen, D-37073 Göttingen, Germany
| | - Uri Weill
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Sarah Gockel
- Department of Cardiology &Pulmonology, Universitätsmedizin Göttingen, D-37075 Göttingen, Germany
| | - Shuh-Yow Lin
- Howard Hughes Medical Institute and Department of Neurobiology, Harvard Medical School, Boston, MA, USA
| | - David P Corey
- Howard Hughes Medical Institute and Department of Neurobiology, Harvard Medical School, Boston, MA, USA
| | - Tobias Kohl
- Department of Cardiology &Pulmonology, Universitätsmedizin Göttingen, D-37075 Göttingen, Germany
| | - Philipp Ströbel
- Institute of Pathology, Universitätsmedizin Göttingen, D-37073 Göttingen, Germany
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Blanche Schwappach
- Department of Molecular Biology, Universitätsmedizin Göttingen, D-37073 Göttingen, Germany.,Max-Planck Institute for Biophysical Chemistry, D-37077, Göttingen, Germany
| | - Fabio Vilardi
- Department of Molecular Biology, Universitätsmedizin Göttingen, D-37073 Göttingen, Germany
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92
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Jungfleisch J, Nedialkova DD, Dotu I, Sloan KE, Martinez-Bosch N, Brüning L, Raineri E, Navarro P, Bohnsack MT, Leidel SA, Díez J. A novel translational control mechanism involving RNA structures within coding sequences. Genome Res 2016; 27:95-106. [PMID: 27821408 PMCID: PMC5204348 DOI: 10.1101/gr.209015.116] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Accepted: 11/03/2016] [Indexed: 12/20/2022]
Abstract
The impact of RNA structures in coding sequences (CDS) within mRNAs is poorly understood. Here, we identify a novel and highly conserved mechanism of translational control involving RNA structures within coding sequences and the DEAD-box helicase Dhh1. Using yeast genetics and genome-wide ribosome profiling analyses, we show that this mechanism, initially derived from studies of the Brome Mosaic virus RNA genome, extends to yeast and human mRNAs highly enriched in membrane and secreted proteins. All Dhh1-dependent mRNAs, viral and cellular, share key common features. First, they contain long and highly structured CDSs, including a region located around nucleotide 70 after the translation initiation site; second, they are directly bound by Dhh1 with a specific binding distribution; and third, complementary experimental approaches suggest that they are activated by Dhh1 at the translation initiation step. Our results show that ribosome translocation is not the only unwinding force of CDS and uncover a novel layer of translational control that involves RNA helicases and RNA folding within CDS providing novel opportunities for regulation of membrane and secretome proteins.
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Affiliation(s)
- Jennifer Jungfleisch
- Molecular Virology Group, Department of Experimental and Health Sciences, Universitat Pompeu Fabra, 08003 Barcelona, Spain
| | - Danny D Nedialkova
- Max Planck Research Group for RNA Biology, Max Planck Institute for Molecular Biomedicine, 48149 Münster, Germany.,Cells-in-Motion Cluster of Excellence, University of Münster, 48149 Münster, Germany
| | - Ivan Dotu
- Research Programme on Biomedical Informatics (GRIB), Department of Experimental and Health Sciences, Universitat Pompeu Fabra, Hospital del Mar Medical Research Institute (IMIM), 08003 Barcelona, Spain
| | - Katherine E Sloan
- Institute for Molecular Biology, Göttingen University Medical Department, 37073 Göttingen, Germany
| | - Neus Martinez-Bosch
- Program of Cancer Research, Hospital del Mar Medical Research Institute (IMIM), 08003 Barcelona, Spain
| | - Lukas Brüning
- Institute for Molecular Biology, Göttingen University Medical Department, 37073 Göttingen, Germany
| | - Emanuele Raineri
- Statistical Genomics, Centro Nacional de Analisis Genomica, 08028 Barcelona, Spain
| | - Pilar Navarro
- Program of Cancer Research, Hospital del Mar Medical Research Institute (IMIM), 08003 Barcelona, Spain
| | - Markus T Bohnsack
- Institute for Molecular Biology, Göttingen University Medical Department, 37073 Göttingen, Germany.,Göttingen Center for Molecular Biosciences, Georg-August University, 37073 Göttingen, Germany
| | - Sebastian A Leidel
- Max Planck Research Group for RNA Biology, Max Planck Institute for Molecular Biomedicine, 48149 Münster, Germany.,Cells-in-Motion Cluster of Excellence, University of Münster, 48149 Münster, Germany.,Faculty of Medicine, University of Münster, 48149 Münster, Germany
| | - Juana Díez
- Molecular Virology Group, Department of Experimental and Health Sciences, Universitat Pompeu Fabra, 08003 Barcelona, Spain
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93
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Cotranslational Intersection between the SRP and GET Targeting Pathways to the Endoplasmic Reticulum of Saccharomyces cerevisiae. Mol Cell Biol 2016; 36:2374-83. [PMID: 27354063 DOI: 10.1128/mcb.00131-16] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 06/17/2016] [Indexed: 01/21/2023] Open
Abstract
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.
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94
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Global profiling of SRP interaction with nascent polypeptides. Nature 2016; 536:219-23. [PMID: 27487212 DOI: 10.1038/nature19070] [Citation(s) in RCA: 98] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2016] [Accepted: 06/29/2016] [Indexed: 12/23/2022]
Abstract
Signal recognition particle (SRP) is a universally conserved protein-RNA complex that mediates co-translational protein translocation and membrane insertion by targeting translating ribosomes to membrane translocons. The existence of parallel co- and post-translational transport pathways, however, raises the question of the cellular substrate pool of SRP and the molecular basis of substrate selection. Here we determine the binding sites of bacterial SRP within the nascent proteome of Escherichia coli at amino acid resolution, by sequencing messenger RNA footprints of ribosome-nascent-chain complexes associated with SRP. SRP, on the basis of its strong preference for hydrophobic transmembrane domains (TMDs), constitutes a compartment-specific targeting factor for nascent inner membrane proteins (IMPs) that efficiently excludes signal-sequence-containing precursors of periplasmic and outer membrane proteins. SRP associates with hydrophobic TMDs enriched in consecutive stretches of hydrophobic and bulky aromatic amino acids immediately on their emergence from the ribosomal exit tunnel. By contrast with current models, N-terminal TMDs are frequently skipped and TMDs internal to the polypeptide sequence are selectively recognized. Furthermore, SRP binds several TMDs in many multi-spanning membrane proteins, suggesting cycles of SRP-mediated membrane targeting. SRP-mediated targeting is not accompanied by a transient slowdown of translation and is not influenced by the ribosome-associated chaperone trigger factor (TF), which has a distinct substrate pool and acts at different stages during translation. Overall, our proteome-wide data set of SRP-binding sites reveals the underlying principles of pathway decisions for nascent chains in bacteria, with SRP acting as the dominant triaging factor, sufficient to separate IMPs from substrates of the SecA-SecB post-translational translocation and TF-assisted cytosolic protein folding pathways.
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95
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Chartron JW, Hunt KCL, Frydman J. Cotranslational signal-independent SRP preloading during membrane targeting. Nature 2016; 536:224-8. [PMID: 27487213 PMCID: PMC5120976 DOI: 10.1038/nature19309] [Citation(s) in RCA: 119] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2015] [Accepted: 07/18/2016] [Indexed: 12/24/2022]
Abstract
Ribosome-associated factors must faithfully decode the limited information available in nascent polypeptides to direct them to their correct cellular fate1. It is unclear how the low complexity information exposed by the nascent chain suffices for accurate recognition by the many factors competing for the limited surface near the ribosomal exit site2,3. Questions remain even for the well-studied cotranslational targeting cycle to the endoplasmic reticulum (ER), involving recognition of linear hydrophobic Signal Sequences (SS) or Transmembrane Domains (TMD) by the Signal Recognition Particle (SRP)4,5. Intriguingly, SRP is in low abundance relative to the large number of ribosome nascent chain complexes (RNCs), yet it accurately selects those destined to the ER6. Despite their overlapping specificities, SRP and the cotranslational Hsp70 SSB display exquisite mutually exclusive selectivity in vivo for their cognate RNCs7,8. To understand cotranslational nascent chain recognition in vivo, we interrogated the cotranslational membrane targeting cycle using ribosome profiling (herein Ribo-seq)9 coupled with biochemical fractionation of ribosome populations. Unexpectedly, SRP preferentially binds secretory RNCs before targeting signals are translated. We show non-coding mRNA elements can promote this signal-independent SRP pre-recruitment. Our study defines the complex kinetic interplay between elongation and determinants in the polypeptide and mRNA modulating SRP-substrate selection and membrane targeting.
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96
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Pfeffer S, Dudek J, Zimmermann R, Förster F. Organization of the native ribosome-translocon complex at the mammalian endoplasmic reticulum membrane. Biochim Biophys Acta Gen Subj 2016; 1860:2122-9. [PMID: 27373685 DOI: 10.1016/j.bbagen.2016.06.024] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Revised: 06/24/2016] [Accepted: 06/28/2016] [Indexed: 11/17/2022]
Abstract
BACKGROUND In eukaryotic cells, many proteins have to be transported across or inserted into the endoplasmic reticulum membrane during their biogenesis on the ribosome. This process is facilitated by the protein translocon, a highly dynamic multi-subunit membrane protein complex. SCOPE OF REVIEW The aim of this review is to summarize the current structural knowledge about protein translocon components in mammals. MAJOR CONCLUSIONS Various structural biology approaches have been used in synergy to characterize the translocon in recent years. X-ray crystallography and cryoelectron microscopy single particle analysis have yielded highly detailed insights into the structure and functional mechanism of the protein-conducting channel Sec61, which constitutes the functional core of the translocon. Cryoelectron tomography and subtomogram analysis have advanced our understanding of the overall structure, molecular organization and compositional heterogeneity of the translocon in a native membrane environment. Tomography densities at subnanometer resolution revealed an intricate network of interactions between the ribosome, Sec61 and accessory translocon components that assist in protein transport, membrane insertion and maturation. GENERAL SIGNIFICANCE The protein translocon is a gateway for approximately one third of all synthesized proteins and numerous human diseases are associated with malfunctioning of its components. Thus, detailed insights into the structure and molecular organization of the translocon will not only advance our understanding of membrane protein biogenesis in general, but they can potentially pave the way for novel therapeutic approaches against human diseases.
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Affiliation(s)
- Stefan Pfeffer
- Max-Planck Institute of Biochemistry, Department of Molecular Structural Biology, D-82152 Martinsried, Germany
| | - Johanna Dudek
- Saarland University, Medical Biochemistry and Molecular Biology, D-66421 Homburg, Germany
| | - Richard Zimmermann
- Saarland University, Medical Biochemistry and Molecular Biology, D-66421 Homburg, Germany.
| | - Friedrich Förster
- Max-Planck Institute of Biochemistry, Department of Molecular Structural Biology, D-82152 Martinsried, Germany; Cryo-Electron Microscopy, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
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97
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Barrero JJ, Papanikou E, Casler JC, Day KJ, Glick BS. An improved reversibly dimerizing mutant of the FK506-binding protein FKBP. CELLULAR LOGISTICS 2016; 6:e1204848. [PMID: 27738551 PMCID: PMC5058350 DOI: 10.1080/21592799.2016.1204848] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Accepted: 06/14/2016] [Indexed: 01/10/2023]
Abstract
FK506-binding protein (FKBP) is a monomer that binds to FK506, rapamycin, and related ligands. The F36M substitution, in which Phe36 in the ligand-binding pocket is changed to Met, leads to formation of antiparallel FKBP dimers, which can be dissociated into monomers by ligand binding. This FKBP(M) mutant has been employed in the mammalian secretory pathway to generate aggregates that can be dissolved by ligand addition to create cargo waves. However, when testing this approach in yeast, we found that dissolution of FKBP(M) aggregates was inefficient. An improved reversibly dimerizing FKBP formed aggregates that dissolved more readily. This FKBP(L,V) mutant carries the F36L mutation, which increases the affinity of ligand binding, and the I90V mutation, which accelerates ligand-induced dissociation of the dimers. The FKBP(L,V) mutant expands the utility of reversibly dimerizing FKBP.
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Affiliation(s)
- Juan J Barrero
- Department of Molecular Genetics and Cell Biology, University of Chicago , Chicago, IL, USA
| | - Effrosyni Papanikou
- Department of Molecular Genetics and Cell Biology, University of Chicago , Chicago, IL, USA
| | - Jason C Casler
- Department of Molecular Genetics and Cell Biology, University of Chicago , Chicago, IL, USA
| | - Kasey J Day
- Department of Molecular Genetics and Cell Biology, University of Chicago , Chicago, IL, USA
| | - Benjamin S Glick
- Department of Molecular Genetics and Cell Biology, University of Chicago , Chicago, IL, USA
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98
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Ast T, Michaelis S, Schuldiner M. The Protease Ste24 Clears Clogged Translocons. Cell 2016; 164:103-114. [PMID: 26771486 DOI: 10.1016/j.cell.2015.11.053] [Citation(s) in RCA: 78] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2015] [Revised: 09/23/2015] [Accepted: 11/17/2015] [Indexed: 01/12/2023]
Abstract
Translocation into the endoplasmic reticulum (ER) is the first step in the biogenesis of thousands of eukaryotic endomembrane proteins. Although functional ER translocation has been avidly studied, little is known about the quality control mechanisms that resolve faulty translocational states. One such faulty state is translocon clogging, in which the substrate fails to properly translocate and obstructs the translocon pore. To shed light on the machinery required to resolve clogging, we carried out a systematic screen in Saccharomyces cerevisiae that highlighted a role for the ER metalloprotease Ste24. We could demonstrate that Ste24 approaches the translocon upon clogging, and it interacts with and generates cleavage fragments of the clogged protein. Importantly, these functions are conserved in the human homolog, ZMPSTE24, although disease-associated mutant forms of ZMPSTE24 fail to clear the translocon. These results shed light on a new and critical task of Ste24, which safeguards the essential process of translocation.
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Affiliation(s)
- Tslil Ast
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Susan Michaelis
- Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel.
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99
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Voorhees RM, Hegde RS. Toward a structural understanding of co-translational protein translocation. Curr Opin Cell Biol 2016; 41:91-9. [PMID: 27155805 DOI: 10.1016/j.ceb.2016.04.009] [Citation(s) in RCA: 72] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2016] [Revised: 04/22/2016] [Accepted: 04/25/2016] [Indexed: 01/06/2023]
Abstract
The translocation of most eukaryotic secreted and integral membrane proteins occurs co-translationally at the endoplasmic reticulum (ER). These nascent polypeptides are recognized on the ribosome by the signal recognition particle (SRP), targeted to the ER, and translocated across or inserted into the membrane by the Sec61 translocation channel. Structural analysis of these co-translational processes has been challenging due to the size, complexity, and flexibility of the targeting and translocation machinery. Recent technological advances in cryo-electron microscopy (cryo-EM) have resulted in increasingly powerful tools to study large, heterogeneous, and low-abundance samples. These advances are being utilized to obtain near-atomic resolution reconstructions of functional translation, targeting, and translocation intermediates, paving the way to a mechanistic understanding of protein biogenesis.
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Affiliation(s)
- Rebecca M Voorhees
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
| | - Ramanujan S Hegde
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom.
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100
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Neubert P, Halim A, Zauser M, Essig A, Joshi HJ, Zatorska E, Larsen ISB, Loibl M, Castells-Ballester J, Aebi M, Clausen H, Strahl S. Mapping the O-Mannose Glycoproteome in Saccharomyces cerevisiae. Mol Cell Proteomics 2016; 15:1323-37. [PMID: 26764011 PMCID: PMC4824858 DOI: 10.1074/mcp.m115.057505] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Indexed: 11/17/2022] Open
Abstract
O-Mannosylation is a vital protein modification conserved from fungi to humans. Yeast is a perfect model to study this post-translational modification, because in contrast to mammals O-mannosylation is the only type of O-glycosylation. In an essential step toward the full understanding of protein O-mannosylation we mapped the O-mannose glycoproteome in baker's yeast. Taking advantage of an O-glycan elongation deficient yeast strain to simplify sample complexity, we identified over 500 O-glycoproteins from all subcellular compartments for which over 2300 O-mannosylation sites were mapped by electron-transfer dissociation (ETD)-based MS/MS. In this study, we focus on the 293 O-glycoproteins (over 1900 glycosylation sites identified by ETD-MS/MS) that enter the secretory pathway and are targets of ER-localized protein O-mannosyltransferases. We find that O-mannosylation is not only a prominent modification of cell wall and plasma membrane proteins, but also of a large number of proteins from the secretory pathway with crucial functions in protein glycosylation, folding, quality control, and trafficking. The analysis of glycosylation sites revealed that O-mannosylation is favored in unstructured regions and β-strands. Furthermore, O-mannosylation is impeded in the proximity of N-glycosylation sites suggesting the interplay of these types of post-translational modifications. The detailed knowledge of the target proteins and their O-mannosylation sites opens for discovery of new roles of this essential modification in eukaryotes, and for a first glance on the evolution of different types of O-glycosylation from yeast to mammals.
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Affiliation(s)
- Patrick Neubert
- From the ‡Centre for Organismal Studies (COS), Department of Cell Chemistry, Heidelberg University, Im Neuenheimer Feld 360, D-69120 Heidelberg, Germany
| | - Adnan Halim
- §Copenhagen Center for Glycomics, Departments of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
| | - Martin Zauser
- From the ‡Centre for Organismal Studies (COS), Department of Cell Chemistry, Heidelberg University, Im Neuenheimer Feld 360, D-69120 Heidelberg, Germany
| | - Andreas Essig
- ¶Institute of Microbiology, Department of Biology, Swiss Federal Institute of Technology, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Hiren J Joshi
- §Copenhagen Center for Glycomics, Departments of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
| | - Ewa Zatorska
- From the ‡Centre for Organismal Studies (COS), Department of Cell Chemistry, Heidelberg University, Im Neuenheimer Feld 360, D-69120 Heidelberg, Germany
| | - Ida Signe Bohse Larsen
- §Copenhagen Center for Glycomics, Departments of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
| | - Martin Loibl
- From the ‡Centre for Organismal Studies (COS), Department of Cell Chemistry, Heidelberg University, Im Neuenheimer Feld 360, D-69120 Heidelberg, Germany
| | - Joan Castells-Ballester
- From the ‡Centre for Organismal Studies (COS), Department of Cell Chemistry, Heidelberg University, Im Neuenheimer Feld 360, D-69120 Heidelberg, Germany
| | - Markus Aebi
- ¶Institute of Microbiology, Department of Biology, Swiss Federal Institute of Technology, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Henrik Clausen
- §Copenhagen Center for Glycomics, Departments of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
| | - Sabine Strahl
- From the ‡Centre for Organismal Studies (COS), Department of Cell Chemistry, Heidelberg University, Im Neuenheimer Feld 360, D-69120 Heidelberg, Germany;
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