1
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Gemmer M, Chaillet ML, Förster F. Exploring the molecular composition of the multipass translocon in its native membrane environment. Life Sci Alliance 2024; 7:e202302496. [PMID: 38866426 PMCID: PMC11169918 DOI: 10.26508/lsa.202302496] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Revised: 05/22/2024] [Accepted: 05/23/2024] [Indexed: 06/14/2024] Open
Abstract
Multispanning membrane proteins are inserted into the endoplasmic reticulum membrane by the ribosome-bound multipass translocon (MPT) machinery. Based on cryo-electron tomography and extensive subtomogram analysis, we reveal the composition and arrangement of ribosome-bound MPT components in their native membrane environment. The intramembrane chaperone complex PAT and the translocon-associated protein (TRAP) complex associate substoichiometrically with the MPT in a translation-dependent manner. Although PAT is preferentially part of MPTs bound to translating ribosomes, the abundance of TRAP is highest in MPTs associated with non-translating ribosomes. The subtomogram average of the TRAP-containing MPT reveals intermolecular contacts between the luminal domains of TRAP and an unknown subunit of the back-of-Sec61 complex. AlphaFold modeling suggests this protein is nodal modulator, bridging the luminal domains of nicalin and TRAPα. Collectively, our results visualize the variability of MPT factors in the native membrane environment dependent on the translational activity of the bound ribosome.
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Affiliation(s)
- Max Gemmer
- https://ror.org/04pp8hn57 Structural Biochemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht, Netherlands
| | - Marten L Chaillet
- https://ror.org/04pp8hn57 Structural Biochemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht, Netherlands
| | - Friedrich Förster
- https://ror.org/04pp8hn57 Structural Biochemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht, Netherlands
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2
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Duart G, Graña-Montes R, Pastor-Cantizano N, Mingarro I. Experimental and computational approaches for membrane protein insertion and topology determination. Methods 2024; 226:102-119. [PMID: 38604415 DOI: 10.1016/j.ymeth.2024.03.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Revised: 03/13/2024] [Accepted: 03/22/2024] [Indexed: 04/13/2024] Open
Abstract
Membrane proteins play pivotal roles in a wide array of cellular processes and constitute approximately a quarter of the protein-coding genes across all organisms. Despite their ubiquity and biological significance, our understanding of these proteins remains notably less comprehensive compared to their soluble counterparts. This disparity in knowledge can be attributed, in part, to the inherent challenges associated with employing specialized techniques for the investigation of membrane protein insertion and topology. This review will center on a discussion of molecular biology methodologies and computational prediction tools designed to elucidate the insertion and topology of helical membrane proteins.
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Affiliation(s)
- Gerard Duart
- Departament de Bioquímica i Biologia Molecular, Institut Universitari de Biotecnologia i Biomedicina (BIOTECMED), Universitat de València, E-46100 Burjassot, Spain
| | - Ricardo Graña-Montes
- Departament de Bioquímica i Biologia Molecular, Institut Universitari de Biotecnologia i Biomedicina (BIOTECMED), Universitat de València, E-46100 Burjassot, Spain
| | - Noelia Pastor-Cantizano
- Departament de Bioquímica i Biologia Molecular, Institut Universitari de Biotecnologia i Biomedicina (BIOTECMED), Universitat de València, E-46100 Burjassot, Spain
| | - Ismael Mingarro
- Departament de Bioquímica i Biologia Molecular, Institut Universitari de Biotecnologia i Biomedicina (BIOTECMED), Universitat de València, E-46100 Burjassot, Spain.
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3
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Karki S, Javanainen M, Rehan S, Tranter D, Kellosalo J, Huiskonen JT, Happonen L, Paavilainen V. Molecular view of ER membrane remodeling by the Sec61/TRAP translocon. EMBO Rep 2023; 24:e57910. [PMID: 37983950 DOI: 10.15252/embr.202357910] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Revised: 10/27/2023] [Accepted: 11/01/2023] [Indexed: 11/22/2023] Open
Abstract
Protein translocation across the endoplasmic reticulum (ER) membrane is an essential step during protein entry into the secretory pathway. The conserved Sec61 protein-conducting channel facilitates polypeptide translocation and coordinates cotranslational polypeptide-processing events. In cells, the majority of Sec61 is stably associated with a heterotetrameric membrane protein complex, the translocon-associated protein complex (TRAP), yet the mechanism by which TRAP assists in polypeptide translocation remains unknown. Here, we present the structure of the core Sec61/TRAP complex bound to a mammalian ribosome by cryogenic electron microscopy (cryo-EM). Ribosome interactions anchor the Sec61/TRAP complex in a conformation that renders the ER membrane locally thinner by significantly curving its lumenal leaflet. We propose that TRAP stabilizes the ribosome exit tunnel to assist nascent polypeptide insertion through Sec61 and provides a ratcheting mechanism into the ER lumen mediated by direct polypeptide interactions.
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Affiliation(s)
- Sudeep Karki
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
| | - Matti Javanainen
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
| | - Shahid Rehan
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
- Protein Biochemistry and Structural Biology, Omass Therapeutics Ltd, Oxford, UK
| | - Dale Tranter
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
| | - Juho Kellosalo
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
| | - Juha T Huiskonen
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
| | - Lotta Happonen
- Division of Infection Medicine, Department of Clinical Sciences, Lund University, Lund, Sweden
| | - Ville Paavilainen
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
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4
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Wang T, Wang C, Wang J, Wang B. An Intrabody against B-Cell Receptor-Associated Protein 31 (BAP31) Suppresses the Glycosylation of the Epithelial Cell-Adhesion Molecule (EpCAM) via Affecting the Formation of the Sec61-Translocon-Associated Protein (TRAP) Complex. Int J Mol Sci 2023; 24:14787. [PMID: 37834237 PMCID: PMC10572819 DOI: 10.3390/ijms241914787] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Revised: 09/12/2023] [Accepted: 09/21/2023] [Indexed: 10/15/2023] Open
Abstract
The epithelial cell-adhesion molecule (EpCAM) is hyperglycosylated in carcinoma tissue and the oncogenic function of EpCAM primarily depends on the degree of glycosylation. Inhibiting EpCAM glycosylation is expected to have an inhibitory effect on cancer. We analyzed the relationship of BAP31 with 84 kinds of tumor-associated antigens and found that BAP31 is positively correlated with the protein level of EpCAM. Triple mutations of EpCAM N76/111/198A, which are no longer modified by glycosylation, were constructed to determine whether BAP31 has an effect on the glycosylation of EpCAM. Plasmids containing different C-termini of BAP31 were constructed to identify the regions of BAP31 that affects EpCAM glycosylation. Antibodies against BAP31 (165-205) were screened from a human phage single-domain antibody library and the effect of the antibody (VH-F12) on EpCAM glycosylation and anticancer was investigated. BAP31 increases protein levels of EpCAM by promoting its glycosylation. The amino acid region from 165 to 205 in BAP31 plays an important role in regulating the glycosylation of EpCAM. The antibody VH-F12 significantly inhibited glycosylation of EpCAM which, subsequently, reduced the adhesion of gastric cancer cells, inducing cytotoxic autophagy, inhibiting the AKT-PI3K-mTOR signaling pathway, and, finally, resulting in proliferation inhibition both in vitro and in vivo. Finally, we clarified that BAP31 plays a key role in promoting N-glycosylation of EpCAM by affecting the Sec61 translocation channels. Altogether, these data implied that BAP31 regulates the N-glycosylation of EpCAM and may represent a potential therapeutic target for cancer therapy.
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Affiliation(s)
| | | | | | - Bing Wang
- College of Life Science and Health, Northeastern University, 195 Chuangxin Road, Hunnan District, Shenyang 110819, China; (T.W.); (C.W.); (J.W.)
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5
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Jung M, Zimmermann R. Quantitative Mass Spectrometry Characterizes Client Spectra of Components for Targeting of Membrane Proteins to and Their Insertion into the Membrane of the Human ER. Int J Mol Sci 2023; 24:14166. [PMID: 37762469 PMCID: PMC10532041 DOI: 10.3390/ijms241814166] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Revised: 09/07/2023] [Accepted: 09/12/2023] [Indexed: 09/29/2023] Open
Abstract
To elucidate the redundancy in the components for the targeting of membrane proteins to the endoplasmic reticulum (ER) and/or their insertion into the ER membrane under physiological conditions, we previously analyzed different human cells by label-free quantitative mass spectrometry. The HeLa and HEK293 cells had been depleted of a certain component by siRNA or CRISPR/Cas9 treatment or were deficient patient fibroblasts and compared to the respective control cells by differential protein abundance analysis. In addition to clients of the SRP and Sec61 complex, we identified membrane protein clients of components of the TRC/GET, SND, and PEX3 pathways for ER targeting, and Sec62, Sec63, TRAM1, and TRAP as putative auxiliary components of the Sec61 complex. Here, a comprehensive evaluation of these previously described differential protein abundance analyses, as well as similar analyses on the Sec61-co-operating EMC and the characteristics of the topogenic sequences of the various membrane protein clients, i.e., the client spectra of the components, are reported. As expected, the analysis characterized membrane protein precursors with cleavable amino-terminal signal peptides or amino-terminal transmembrane helices as predominant clients of SRP, as well as the Sec61 complex, while precursors with more central or even carboxy-terminal ones were found to dominate the client spectra of the SND and TRC/GET pathways for membrane targeting. For membrane protein insertion, the auxiliary Sec61 channel components indeed share the client spectra of the Sec61 complex to a large extent. However, we also detected some unexpected differences, particularly related to EMC, TRAP, and TRAM1. The possible mechanistic implications for membrane protein biogenesis at the human ER are discussed and can be expected to eventually advance our understanding of the mechanisms that are involved in the so-called Sec61-channelopathies, resulting from deficient ER protein import.
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Affiliation(s)
| | - Richard Zimmermann
- Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany;
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6
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Pauwels E, Shewakramani NR, De Wijngaert B, Camps A, Provinciael B, Stroobants J, Kalies KU, Hartmann E, Maes P, Vermeire K, Das K. Structural insights into TRAP association with ribosome-Sec61 complex and translocon inhibition by a CADA derivative. SCIENCE ADVANCES 2023; 9:eadf0797. [PMID: 36867692 PMCID: PMC9984176 DOI: 10.1126/sciadv.adf0797] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Accepted: 01/31/2023] [Indexed: 05/26/2023]
Abstract
During cotranslational translocation, the signal peptide of a nascent chain binds Sec61 translocon to initiate protein transport through the endoplasmic reticulum (ER) membrane. Our cryo-electron microscopy structure of ribosome-Sec61 shows binding of an ordered heterotetrameric translocon-associated protein (TRAP) complex, in which TRAP-γ is anchored at two adjacent positions of 28S ribosomal RNA and interacts with ribosomal protein L38 and Sec61α/γ. Four transmembrane helices (TMHs) of TRAP-γ cluster with one C-terminal helix of each α, β, and δ subunits. The seven TMH bundle helps position a crescent-shaped trimeric TRAP-α/β/δ core in the ER lumen, facing the Sec61 channel. Further, our in vitro assay establishes the cyclotriazadisulfonamide derivative CK147 as a translocon inhibitor. A structure of ribosome-Sec61-CK147 reveals CK147 binding the channel and interacting with the plug helix from the lumenal side. The CK147 resistance mutations surround the inhibitor. These structures help in understanding the TRAP functions and provide a new Sec61 site for designing translocon inhibitors.
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Affiliation(s)
- Eva Pauwels
- Department of Microbiology, Immunology, and Transplantation, KU Leuven, Leuven 3000, Belgium
- Laboratory of Virology and Chemotherapy, Rega Institute for Medical Research, KU Leuven, Leuven 3000, Belgium
| | - Neesha R. Shewakramani
- Department of Microbiology, Immunology, and Transplantation, KU Leuven, Leuven 3000, Belgium
- Laboratory of Virology and Chemotherapy, Rega Institute for Medical Research, KU Leuven, Leuven 3000, Belgium
| | - Brent De Wijngaert
- Department of Microbiology, Immunology, and Transplantation, KU Leuven, Leuven 3000, Belgium
- Laboratory of Virology and Chemotherapy, Rega Institute for Medical Research, KU Leuven, Leuven 3000, Belgium
| | - Anita Camps
- Department of Microbiology, Immunology, and Transplantation, KU Leuven, Leuven 3000, Belgium
- Laboratory of Virology and Chemotherapy, Rega Institute for Medical Research, KU Leuven, Leuven 3000, Belgium
| | - Becky Provinciael
- Department of Microbiology, Immunology, and Transplantation, KU Leuven, Leuven 3000, Belgium
- Laboratory of Virology and Chemotherapy, Rega Institute for Medical Research, KU Leuven, Leuven 3000, Belgium
| | - Joren Stroobants
- Department of Microbiology, Immunology, and Transplantation, KU Leuven, Leuven 3000, Belgium
- Laboratory of Virology and Chemotherapy, Rega Institute for Medical Research, KU Leuven, Leuven 3000, Belgium
| | - Kai-Uwe Kalies
- Centre for Structural and Cell Biology in Medicine, Institute of Biology, University of Lübeck, Lübeck 23562, Germany
| | - Enno Hartmann
- Centre for Structural and Cell Biology in Medicine, Institute of Biology, University of Lübeck, Lübeck 23562, Germany
| | - Piet Maes
- Department of Microbiology, Immunology, and Transplantation, KU Leuven, Leuven 3000, Belgium
- Laboratory of Clinical and Epidemiological Virology, Rega Institute for Medical Research, KU Leuven, Leuven 3000, Belgium
| | - Kurt Vermeire
- Department of Microbiology, Immunology, and Transplantation, KU Leuven, Leuven 3000, Belgium
- Laboratory of Virology and Chemotherapy, Rega Institute for Medical Research, KU Leuven, Leuven 3000, Belgium
| | - Kalyan Das
- Department of Microbiology, Immunology, and Transplantation, KU Leuven, Leuven 3000, Belgium
- Laboratory of Virology and Chemotherapy, Rega Institute for Medical Research, KU Leuven, Leuven 3000, Belgium
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7
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Itskanov S, Park E. Mechanism of Protein Translocation by the Sec61 Translocon Complex. Cold Spring Harb Perspect Biol 2023; 15:a041250. [PMID: 35940906 PMCID: PMC9808579 DOI: 10.1101/cshperspect.a041250] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The endoplasmic reticulum (ER) is a major site for protein synthesis, folding, and maturation in eukaryotic cells, responsible for production of secretory proteins and most integral membrane proteins. The universally conserved protein-conducting channel Sec61 complex mediates core steps in these processes by translocating hydrophilic polypeptide segments of client proteins across the ER membrane and integrating hydrophobic transmembrane segments into the membrane. The Sec61 complex associates with several other molecular machines and enzymes to enable substrate engagement with the channel and coordination of protein translocation with translation, protein folding, and/or post-translational modifications. Recent cryo-electron microscopy and functional studies of these translocon complexes have greatly advanced our mechanistic understanding of Sec61-dependent protein biogenesis at the ER. Here, we will review the current models for how the Sec61 channel performs its functions in coordination with partner complexes.
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Affiliation(s)
- Samuel Itskanov
- Biophysics Graduate Program
- California Institute for Quantitative Biosciences
| | - Eunyong Park
- California Institute for Quantitative Biosciences
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720, USA
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8
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Abstract
More than 30% of eukaryotic proteins contain domains that must translocate across or integrate into the endoplasmic reticulum (ER) membrane. With few exceptions, protein translocation and transmembrane domain integration at the ER require the conserved Sec61 translocon. Decades of studies have established a clear mechanistic model for how the Sec61 translocon functions. The biosynthesis of distinct subsets of proteins at the ER also involves accessory factors that interact with the Sec61 translocon and translocating nascent proteins. However, assigning specific functions to many translocon accessory factors has been a persistent challenge in the field. This Perspective discusses recent insights into mechanisms that promote protein biosynthesis at the ER through accessory factors that directly regulate the Sec61 translocon or chaperone nascent proteins within the ER membrane. These translocon accessory factor functions, and more still to be discovered, are essential for producing a diverse and high-fidelity proteome at the ER.
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Affiliation(s)
- Sichen Shao
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115,*Address correspondence to: Sichen Shao ()
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9
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Wang J, Gou X, Wang X, Zhang J, Zhao N, Wang X. Case Report: The novel hemizygous mutation in the SSR4 gene caused congenital disorder of glycosylation type iy: A case study and literature review. Front Genet 2022; 13:955732. [PMID: 36386804 PMCID: PMC9643473 DOI: 10.3389/fgene.2022.955732] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2022] [Accepted: 10/10/2022] [Indexed: 12/05/2022] Open
Abstract
Background: Recently, the hemizygous variation of SSR4 gene has been reported to be associated with congenital disorder of glycosylation type Iy. To date, only 13 patients have been diagnosed with SSR4-CDG in the worldwide, but it has not been reported in the Chinese population. Methods: Whole-exome sequencing and gene copy number variation analysis were used to genetic analysis. The mRNA expression of SSR4 gene in blood was detected by Real-time Quantitative PCR. The clinical manifestations of all patients reported in the literature were reviewed. Results: WES analysis identified a de novo hemizygous variant c.269G>A (p.Trp90*) of SSR4 gene in the proband with psychomotor retardation, microcephaly, abnormal facial features, and nystagmus. This variant has not been reported in previous studies. The in vivo mRNA expression of SSR4 gene in patient was significantly decreased. Literature review showed that all 14 patients, including our patient, presented with hypotonia, intellectual disability, developmental delay, microcephaly, and abnormal facial features, while most patients had feeding difficulties, growth retardation, and ocular abnormalities, and epilepsy and skeletal abnormalities are less common. Conclusion: We reported the first case of SSR4-CDG caused by SSR4 variant in Chinese population, expanded the clinical and mutation spectra of the disorder, clarified the genetic etiology of the patient, and offered support for the prenatal diagnosis of the index family.
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10
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Parys JB, Van Coppenolle F. Sec61 complex/translocon: The role of an atypical ER Ca 2+-leak channel in health and disease. Front Physiol 2022; 13:991149. [PMID: 36277220 PMCID: PMC9582130 DOI: 10.3389/fphys.2022.991149] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Accepted: 09/20/2022] [Indexed: 11/02/2023] Open
Abstract
The heterotrimeric Sec61 protein complex forms the functional core of the so-called translocon that forms an aqueous channel in the endoplasmic reticulum (ER). The primary role of the Sec61 complex is to allow protein import in the ER during translation. Surprisingly, a completely different function in intracellular Ca2+ homeostasis has emerged for the Sec61 complex, and the latter is now accepted as one of the major Ca2+-leak pathways of the ER. In this review, we first discuss the structure of the Sec61 complex and focus on the pharmacology and regulation of the Sec61 complex as a Ca2+-leak channel. Subsequently, we will pay particular attention to pathologies that are linked to Sec61 mutations, such as plasma cell deficiency and congenital neutropenia. Finally, we will explore the relevance of the Sec61 complex as a Ca2+-leak channel in various pathophysiological (ER stress, apoptosis, ischemia-reperfusion) and pathological (type 2 diabetes, cancer) settings.
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Affiliation(s)
- Jan B. Parys
- Laboratory for Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine & Leuven Kanker Instituut, KU Leuven, Leuven, Belgium
| | - Fabien Van Coppenolle
- CarMeN Laboratory, INSERM, INRA, INSA Lyon, Université Claude Bernard Lyon 1, Lyon, France
- Groupement Hospitalier EST, Department of Cardiology, Hospices Civils de Lyon, Lyon, France
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11
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Rozov SM, Deineko EV. Increasing the Efficiency of the Accumulation of Recombinant Proteins in Plant Cells: The Role of Transport Signal Peptides. PLANTS (BASEL, SWITZERLAND) 2022; 11:2561. [PMID: 36235427 PMCID: PMC9572730 DOI: 10.3390/plants11192561] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Revised: 09/23/2022] [Accepted: 09/26/2022] [Indexed: 06/16/2023]
Abstract
The problem with increasing the yield of recombinant proteins is resolvable using different approaches, including the transport of a target protein to cell compartments with a low protease activity. In the cell, protein targeting involves short-signal peptide sequences recognized by intracellular protein transport systems. The main systems of the protein transport across membranes of the endoplasmic reticulum and endosymbiotic organelles are reviewed here, as are the major types and structure of the signal sequences targeting proteins to the endoplasmic reticulum and its derivatives, to plastids, and to mitochondria. The role of protein targeting to certain cell organelles depending on specific features of recombinant proteins and the effect of this targeting on the protein yield are discussed, in addition to the main directions of the search for signal sequences based on their primary structure. This knowledge makes it possible not only to predict a protein localization in the cell but also to reveal the most efficient sequences with potential biotechnological utility.
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12
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Lang S, Nguyen D, Bhadra P, Jung M, Helms V, Zimmermann R. Signal Peptide Features Determining the Substrate Specificities of Targeting and Translocation Components in Human ER Protein Import. Front Physiol 2022; 13:833540. [PMID: 35899032 PMCID: PMC9309488 DOI: 10.3389/fphys.2022.833540] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2021] [Accepted: 05/17/2022] [Indexed: 12/11/2022] Open
Abstract
In human cells, approximately 30% of all polypeptides enter the secretory pathway at the level of the endoplasmic reticulum (ER). This process involves cleavable amino-terminal signal peptides (SPs) or more or less amino-terminal transmembrane helices (TMHs), which serve as targeting determinants, at the level of the precursor polypeptides and a multitude of cytosolic and ER proteins, which facilitate their ER import. Alone or in combination SPs and TMHs guarantee the initial ER targeting as well as the subsequent membrane integration or translocation. Cytosolic SRP and SR, its receptor in the ER membrane, mediate cotranslational targeting of most nascent precursor polypeptide chains to the polypeptide-conducting Sec61 complex in the ER membrane. Alternatively, fully-synthesized precursor polypeptides and certain nascent precursor polypeptides are targeted to the ER membrane by either the PEX-, SND-, or TRC-pathway. Although these targeting pathways may have overlapping functions, the question arises how relevant this is under cellular conditions and which features of SPs and precursor polypeptides determine preference for a certain pathway. Irrespective of their targeting pathway(s), most precursor polypeptides are integrated into or translocated across the ER membrane via the Sec61 channel. For some precursor polypeptides specific Sec61 interaction partners have to support the gating of the channel to the open state, again raising the question why and when this is the case. Recent progress shed light on the client spectrum and specificities of some auxiliary components, including Sec62/Sec63, TRAM1 protein, and TRAP. To address the question which precursors use a certain pathway or component in intact human cells, i.e., under conditions of fast translation rates and molecular crowding, in the presence of competing precursors, different targeting organelles, and relevant stoichiometries of the involved components, siRNA-mediated depletion of single targeting or transport components in HeLa cells was combined with label-free quantitative proteomics and differential protein abundance analysis. Here, we present a summary of the experimental approach as well as the resulting differential protein abundance analyses and discuss their mechanistic implications in light of the available structural data.
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Affiliation(s)
- Sven Lang
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
- *Correspondence: Sven Lang, ; Richard Zimmermann,
| | - Duy Nguyen
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Pratiti Bhadra
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Martin Jung
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Volkhard Helms
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Richard Zimmermann
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
- *Correspondence: Sven Lang, ; Richard Zimmermann,
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13
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Whitley P, Grau B, Gumbart JC, Martínez-Gil L, Mingarro I. Folding and Insertion of Transmembrane Helices at the ER. Int J Mol Sci 2021; 22:ijms222312778. [PMID: 34884581 PMCID: PMC8657811 DOI: 10.3390/ijms222312778] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2021] [Revised: 11/22/2021] [Accepted: 11/23/2021] [Indexed: 01/16/2023] Open
Abstract
In eukaryotic cells, the endoplasmic reticulum (ER) is the entry point for newly synthesized proteins that are subsequently distributed to organelles of the endomembrane system. Some of these proteins are completely translocated into the lumen of the ER while others integrate stretches of amino acids into the greasy 30 Å wide interior of the ER membrane bilayer. It is generally accepted that to exist in this non-aqueous environment the majority of membrane integrated amino acids are primarily non-polar/hydrophobic and adopt an α-helical conformation. These stretches are typically around 20 amino acids long and are known as transmembrane (TM) helices. In this review, we will consider how transmembrane helices achieve membrane integration. We will address questions such as: Where do the stretches of amino acids fold into a helical conformation? What is/are the route/routes that these stretches take from synthesis at the ribosome to integration through the ER translocon? How do these stretches ‘know’ to integrate and in which orientation? How do marginally hydrophobic stretches of amino acids integrate and survive as transmembrane helices?
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Affiliation(s)
- Paul Whitley
- Department of Biology and Biochemistry, Centre for Regenerative Medicine, University of Bath, Bath BA2 7AY, UK;
| | - Brayan Grau
- Department of Biochemistry and Molecular Biology, Institute of Biotechnology and Biomedicine (BIOTECMED), Universitat de València, E-46100 Burjassot, Spain; (B.G.); (L.M.-G.)
| | - James C. Gumbart
- School of Physics, School of Chemistry and Biochemistry, Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332, USA;
| | - Luis Martínez-Gil
- Department of Biochemistry and Molecular Biology, Institute of Biotechnology and Biomedicine (BIOTECMED), Universitat de València, E-46100 Burjassot, Spain; (B.G.); (L.M.-G.)
| | - Ismael Mingarro
- Department of Biochemistry and Molecular Biology, Institute of Biotechnology and Biomedicine (BIOTECMED), Universitat de València, E-46100 Burjassot, Spain; (B.G.); (L.M.-G.)
- Correspondence: ; Tel.: +34-963543796
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14
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Take Me Home, Protein Roads: Structural Insights into Signal Peptide Interactions during ER Translocation. Int J Mol Sci 2021; 22:ijms222111871. [PMID: 34769302 PMCID: PMC8584900 DOI: 10.3390/ijms222111871] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Revised: 10/14/2021] [Accepted: 10/28/2021] [Indexed: 11/17/2022] Open
Abstract
Cleavable endoplasmic reticulum (ER) signal peptides (SPs) and other non-cleavable signal sequences target roughly a quarter of the human proteome to the ER. These short peptides, mostly located at the N-termini of proteins, are highly diverse. For most proteins targeted to the ER, it is the interactions between the signal sequences and the various ER targeting and translocation machineries such as the signal recognition particle (SRP), the protein-conducting channel Sec61, and the signal peptidase complex (SPC) that determine the proteins’ target location and provide translocation fidelity. In this review, we follow the signal peptide into the ER and discuss the recent insights that structural biology has provided on the governing principles of those interactions.
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Srinivasan K, Banerjee A, Baid P, Dhur A, Sengupta J. Ribosome-membrane crosstalk: Co-translational targeting pathways of proteins across membranes in prokaryotes and eukaryotes. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2021; 128:163-198. [PMID: 35034718 DOI: 10.1016/bs.apcsb.2021.07.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Ribosomes are the molecular machine of living cells designed for decoding mRNA-encoded genetic information into protein. Being sophisticated machinery, both in design and function, the ribosome not only carries out protein synthesis, but also coordinates several other ribosome-associated cellular processes. One such process is the translocation of proteins across or into the membrane depending on their secretory or membrane-associated nature. These proteins comprise a large portion of a cell's proteome and act as key factors for cellular survival as well as several crucial functional pathways. Protein transport to extra- and intra-cytosolic compartments (across the eukaryotic endoplasmic reticulum (ER) or across the prokaryotic plasma membrane) or insertion into membranes majorly occurs through an evolutionarily conserved protein-conducting channel called translocon (eukaryotic Sec61 or prokaryotic SecYEG channels). Targeting proteins to the membrane-bound translocon may occur via post-translational or co-translational modes and it is often mediated by recognition of an N-terminal signal sequence in the newly synthesizes polypeptide chain. Co-translational translocation is coupled to protein synthesis where the ribosome-nascent chain complex (RNC) itself is targeted to the translocon. Here, in the light of recent advances in structural and functional studies, we discuss our current understanding of the mechanistic models of co-translational translocation, coordinated by the actively translating ribosomes, in prokaryotes and eukaryotes.
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Affiliation(s)
- Krishnamoorthi Srinivasan
- Division of Structural Biology and Bioinformatics, CSIR-Indian Institute of Chemical Biology, Kolkata, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India
| | - Aneek Banerjee
- Division of Structural Biology and Bioinformatics, CSIR-Indian Institute of Chemical Biology, Kolkata, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India
| | - Priya Baid
- Division of Structural Biology and Bioinformatics, CSIR-Indian Institute of Chemical Biology, Kolkata, India
| | - Ankit Dhur
- Division of Structural Biology and Bioinformatics, CSIR-Indian Institute of Chemical Biology, Kolkata, India
| | - Jayati Sengupta
- Division of Structural Biology and Bioinformatics, CSIR-Indian Institute of Chemical Biology, Kolkata, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India.
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Efficient integration of transmembrane domains depends on the folding properties of the upstream sequences. Proc Natl Acad Sci U S A 2021; 118:2102675118. [PMID: 34373330 PMCID: PMC8379923 DOI: 10.1073/pnas.2102675118] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The topology of membrane proteins is defined by the successive integration of α-helical transmembrane domains at the Sec61 translocon. For each polypeptide segment of ∼20 residues entering the translocon, their combined hydrophobicities were previously shown to define membrane integration. Here, we discovered that different sequences preceding a potential transmembrane domain substantially affect the hydrophobicity threshold. Sequences that are rapidly folding, intrinsically disordered, very short, or strongly binding chaperones allow efficient integration at low hydrophobicity. Folding deficient mutant domains and artificial sequences not binding chaperones interfered with membrane integration likely by remaining partially unfolded and exposing hydrophobic surfaces that compete with the translocon for the emerging transmembrane segment, reducing integration efficiency. Rapid folding or strong chaperone binding thus promote efficient integration. The topology of most membrane proteins is defined by the successive integration of α-helical transmembrane domains at the Sec61 translocon. The translocon provides a pore for the transfer of polypeptide segments across the membrane while giving them lateral access to the lipid. For each polypeptide segment of ∼20 residues, the combined hydrophobicities of its constituent amino acids were previously shown to define the extent of membrane integration. Here, we discovered that different sequences preceding a potential transmembrane domain substantially affect its hydrophobicity requirement for integration. Rapidly folding domains, sequences that are intrinsically disordered or very short or capable of binding chaperones with high affinity, allow for efficient transmembrane integration with low-hydrophobicity thresholds for both orientations in the membrane. In contrast, long protein fragments, folding-deficient mutant domains, and artificial sequences not binding chaperones interfered with membrane integration, requiring higher hydrophobicity. We propose that the latter sequences, as they compact on their hydrophobic residues, partially folded but unable to reach a native state, expose hydrophobic surfaces that compete with the translocon for the emerging transmembrane segment, reducing integration efficiency. The results suggest that rapid folding or strong chaperone binding is required for efficient transmembrane integration.
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Klein MC, Lerner M, Nguyen D, Pfeffer S, Dudek J, Förster F, Helms V, Lang S, Zimmermann R. TRAM1 protein may support ER protein import by modulating the phospholipid bilayer near the lateral gate of the Sec61-channel. Channels (Austin) 2021; 14:28-44. [PMID: 32013668 PMCID: PMC7039644 DOI: 10.1080/19336950.2020.1724759] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
In mammalian cells, one-third of all polypeptides is transported into or through the ER-membrane via the Sec61-channel. While the Sec61-complex facilitates the transport of all polypeptides with amino-terminal signal peptides (SP) or SP-equivalent transmembrane helices (TMH), the translocating chain-associated membrane protein (now termed TRAM1) was proposed to support transport of a subset of precursors. To identify possible determinants of TRAM1 substrate specificity, we systematically identified TRAM1-dependent precursors by analyzing cellular protein abundance changes upon TRAM1 depletion in HeLa cells using quantitative label-free proteomics. In contrast to previous analysis after TRAP depletion, SP and TMH analysis of TRAM1 clients did not reveal any distinguishing features that could explain its putative substrate specificity. To further address the TRAM1 mechanism, live-cell calcium imaging was carried out after TRAM1 depletion in HeLa cells. In additional contrast to previous analysis after TRAP depletion, TRAM1 depletion did not affect calcium leakage from the ER. Thus, TRAM1 does not appear to act as SP- or TMH-receptor on the ER-membrane’s cytosolic face and does not appear to affect the open probability of the Sec61-channel. It may rather play a supportive role in protein transport, such as making the phospholipid bilayer conducive for accepting SP and TMH in the vicinity of the lateral gate of the Sec61-channel. Abbreviations: ER, endoplasmic reticulum; OST, oligosaccharyltransferase; RAMP, ribosome-associated membrane protein; SP, signal peptide; SR, SRP-receptor; SRP, signal recognition particle; TMH, signal peptide-equivalent transmembrane helix; TRAM, translocating chain-associated membrane protein; TRAP, translocon-associated protein.
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Affiliation(s)
| | - Monika Lerner
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Duy Nguyen
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | | | - Johanna Dudek
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Friedrich Förster
- Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht, The Netherlands
| | - Volkhard Helms
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Sven Lang
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Richard Zimmermann
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
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Feng Z, Zhao Y, Li T, Nie W, Yang X, Wang X, Wu J, Liao J, Zou Y. CATP-8/P5A ATPase Regulates ER Processing of the DMA-1 Receptor for Dendritic Branching. Cell Rep 2021; 32:108101. [PMID: 32905774 DOI: 10.1016/j.celrep.2020.108101] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2020] [Revised: 06/05/2020] [Accepted: 08/11/2020] [Indexed: 10/23/2022] Open
Abstract
Dendrite morphogenesis is essential for a neuron to establish its receptive field and is, thus, the anatomical basis for the proper functioning of the nervous system. The molecular mechanisms governing dendrite branching are not fully understood. Using the multi-dendritic PVD neuron in the nematode Caenorhabditis elegans, we identify CATP-8/P5A ATPase as a key regulator of dendrite branching that controls the translocation of the DMA-1 receptor to the endoplasmic reticulum (ER). The specific signal peptide of DMA-1 and the ATPase activity of CATP-8 are essential for this process. Our results reveal that P5A ATPase may regulate protein translocation in the ER.
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Affiliation(s)
- Zhigang Feng
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China; Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yupeng Zhao
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Tingting Li
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China; Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Wang Nie
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China; Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Xiaoyan Yang
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China; Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Xinjian Wang
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Jianguo Wu
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Jun Liao
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Yan Zou
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China; Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
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Sicking M, Lang S, Bochen F, Roos A, Drenth JPH, Zakaria M, Zimmermann R, Linxweiler M. Complexity and Specificity of Sec61-Channelopathies: Human Diseases Affecting Gating of the Sec61 Complex. Cells 2021; 10:1036. [PMID: 33925740 PMCID: PMC8147068 DOI: 10.3390/cells10051036] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Revised: 04/15/2021] [Accepted: 04/17/2021] [Indexed: 12/14/2022] Open
Abstract
The rough endoplasmic reticulum (ER) of nucleated human cells has crucial functions in protein biogenesis, calcium (Ca2+) homeostasis, and signal transduction. Among the roughly one hundred components, which are involved in protein import and protein folding or assembly, two components stand out: The Sec61 complex and BiP. The Sec61 complex in the ER membrane represents the major entry point for precursor polypeptides into the membrane or lumen of the ER and provides a conduit for Ca2+ ions from the ER lumen to the cytosol. The second component, the Hsp70-type molecular chaperone immunoglobulin heavy chain binding protein, short BiP, plays central roles in protein folding and assembly (hence its name), protein import, cellular Ca2+ homeostasis, and various intracellular signal transduction pathways. For the purpose of this review, we focus on these two components, their relevant allosteric effectors and on the question of how their respective functional cycles are linked in order to reconcile the apparently contradictory features of the ER membrane, selective permeability for precursor polypeptides, and impermeability for Ca2+. The key issues are that the Sec61 complex exists in two conformations: An open and a closed state that are in a dynamic equilibrium with each other, and that BiP contributes to its gating in both directions in cooperation with different co-chaperones. While the open Sec61 complex forms an aqueous polypeptide-conducting- and transiently Ca2+-permeable channel, the closed complex is impermeable even to Ca2+. Therefore, we discuss the human hereditary and tumor diseases that are linked to Sec61 channel gating, termed Sec61-channelopathies, as disturbances of selective polypeptide-impermeability and/or aberrant Ca2+-permeability.
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Affiliation(s)
- Mark Sicking
- Department of Medical Biochemistry & Molecular Biology, Saarland University, D-66421 Homburg, Germany;
| | - Sven Lang
- Department of Medical Biochemistry & Molecular Biology, Saarland University, D-66421 Homburg, Germany;
| | - Florian Bochen
- Department of Otorhinolaryngology, Head and Neck Surgery, Saarland University Medical Center, D-66421 Homburg, Germany; (F.B.); (M.L.)
| | - Andreas Roos
- Department of Neuropediatrics, Essen University Hospital, D-45147 Essen, Germany;
| | - Joost P. H. Drenth
- Department of Molecular Gastroenterology and Hepatology, Radboud University Medical Center, 6525 GA Nijmegen, The Netherlands;
| | - Muhammad Zakaria
- Department of Genetics, Hazara University, Mansehra 21300, Pakistan;
| | - Richard Zimmermann
- Department of Medical Biochemistry & Molecular Biology, Saarland University, D-66421 Homburg, Germany;
| | - Maximilian Linxweiler
- Department of Otorhinolaryngology, Head and Neck Surgery, Saarland University Medical Center, D-66421 Homburg, Germany; (F.B.); (M.L.)
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20
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Kriegler T, Lang S, Notari L, Hessa T. Prion Protein Translocation Mechanism Revealed by Pulling Force Studies. J Mol Biol 2020; 432:4447-4465. [PMID: 32502491 DOI: 10.1016/j.jmb.2020.05.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Revised: 05/10/2020] [Accepted: 05/28/2020] [Indexed: 11/26/2022]
Abstract
The mammalian prion protein (PrP) engages with the ribosome-Sec61 translocation channel complex to generate different topological variants that are either physiological, or involved in neurodegenerative diseases. Here, we describe cotranslational folding and translocation mechanisms of PrP coupled to an Xbp1-based arrest peptide as folding sensor, to measure forces acting on PrP nascent chain. Our data reveal two main pulling events followed by a minor third one exerted on the nascent chains during their translocation. Using those force landscapes, we show that a specific sequence within an intrinsically disordered region, containing a polybasic and glycine-proline rich residues, modulates the second pulling event by interacting with TRAP complex. This work also delineates the sequence of events involved in generation of PrP toxic transmembrane topologies during its synthesis. Our results shed new insight into the folding of such a topological complex protein, where marginal pulling by the signal sequence, together with the flanking downstream sequence in the mature domain, primarily drives an overall inefficient translocation resulting in the nascent chain to adopt alternative topologies.
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Affiliation(s)
- Theresa Kriegler
- Department of Biochemistry and Biophysics, Arrhenius Laboratories of Natural Sciences, Stockholm University, Svante Arrhenius väg 16C, SE-10691 Stockholm, Sweden
| | - Sven Lang
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Luigi Notari
- Department of Clinical Neuroscience, Therapeutic Immune Design Unit, CMM, L8:02, Karolinska Institutet, Sweden
| | - Tara Hessa
- Department of Biochemistry and Biophysics, Arrhenius Laboratories of Natural Sciences, Stockholm University, Svante Arrhenius väg 16C, SE-10691 Stockholm, Sweden.
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21
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Abstract
In eukaryotic cells, about one-third of the synthesized proteins are translocated into the endoplasmic reticulum; they are membrane or lumen resident proteins and proteins direct to the Golgi apparatus. The co-translational translocation takes place through the heterotrimeric protein-conducting channel Sec61 which is associated with the ribosome and many accessory components, such as the heterotetrameric translocon-associated protein (TRAP) complex. Recently, microscopic techniques, such as cryo-electron microscopy and cryo-electron tomography, have enabled the determination of the translocation machinery structure. However, at present, there is a lack of understanding regarding the roles of some of its components; indeed, the TRAP complex function during co-translational translocation needs to be established. In addition, TRAP may play a role during unfolded protein response, endoplasmic-reticulum-associated protein degradation and congenital disorder of glycosylation (ssr4 CDG). In this article, I describe the current understanding of the TRAP complex in the light of its possible function(s).
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Affiliation(s)
- Antonietta Russo
- Medical Biochemistry and Molecular Biology, UKS, University of Saarland, Homburg, Germany
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22
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Zhang M, Liu L, Lin X, Wang Y, Li Y, Guo Q, Li S, Sun Y, Tao X, Zhang D, Lv X, Zheng L, Ge L. A Translocation Pathway for Vesicle-Mediated Unconventional Protein Secretion. Cell 2020; 181:637-652.e15. [PMID: 32272059 DOI: 10.1016/j.cell.2020.03.031] [Citation(s) in RCA: 125] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 01/22/2020] [Accepted: 03/11/2020] [Indexed: 12/13/2022]
Abstract
Many cytosolic proteins lacking a signal peptide, called leaderless cargoes, are secreted through unconventional secretion. Vesicle trafficking is a major pathway involved. It is unclear how leaderless cargoes enter into the vesicle. Here, we find a translocation pathway regulating vesicle entry and secretion of leaderless cargoes. We identify TMED10 as a protein channel for the vesicle entry and secretion of many leaderless cargoes. The interaction of TMED10 C-terminal region with a motif in the cargo accounts for the selective release of the cargoes. In an in vitro reconstitution assay, TMED10 directly mediates the membrane translocation of leaderless cargoes into the liposome, which is dependent on protein unfolding and enhanced by HSP90s. In the cell, TMED10 localizes on the endoplasmic reticulum (ER)-Golgi intermediate compartment and directs the entry of cargoes into this compartment. Furthermore, cargo induces the formation of TMED10 homo-oligomers which may act as a protein channel for cargo translocation.
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Affiliation(s)
- Min Zhang
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Lei Liu
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Xubo Lin
- Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing 100191, China
| | - Yang Wang
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Ying Li
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Qing Guo
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Shulin Li
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Yuxin Sun
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Xuan Tao
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Di Zhang
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Xiachen Lv
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Li Zheng
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Liang Ge
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.
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Lee S, Shin Y, Kim K, Song Y, Kim Y, Kang SW. Protein Translocation Acquires Substrate Selectivity Through ER Stress-Induced Reassembly of Translocon Auxiliary Components. Cells 2020; 9:cells9020518. [PMID: 32102453 PMCID: PMC7072789 DOI: 10.3390/cells9020518] [Citation(s) in RCA: 3] [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: 02/06/2020] [Revised: 02/20/2020] [Accepted: 02/24/2020] [Indexed: 11/16/2022] Open
Abstract
Protein import across the endoplasmic reticulum membrane is physiologically regulated in a substrate-selective manner to ensure the protection of stressed ER from the overload of misfolded proteins. However, it is poorly understood how different types of substrates are accurately distinguished and disqualified during translocational regulation. In this study, we found poorly assembled translocon-associated protein (TRAP) complexes in stressed ER. Immunoaffinity purification identified calnexin in the TRAP complex in which poor assembly inhibited membrane insertion of the prion protein (PrP) in a transmembrane sequence-selective manner, through translocational regulation. This reaction was induced selectively by redox perturbation, rather than calcium depletion, in the ER. The liberation of ERp57 from calnexin appeared to be the reason for the redox sensitivity. Stress-independent disruption of the TRAP complex prevented a pathogenic transmembrane form of PrP (ctmPrP) from accumulating in the ER. This study uncovered a previously unappreciated role for calnexin in assisting the redox-sensitive function of the TRAP complex and provided insights into the ER stress-induced reassembly of translocon auxiliary components as a key mechanism by which protein translocation acquires substrate selectivity.
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Affiliation(s)
- Sohee Lee
- Department of Biomedical Sciences, University of Ulsan College of Medicine, Seoul 138-736, Korea; (S.L.); (Y.S.); (Y.S.)
- Asan Medical Institute of Convergence Science and Technology, Asan Medical Center, Seoul 05505, Korea
| | - Yejin Shin
- Department of Biomedical Sciences, University of Ulsan College of Medicine, Seoul 138-736, Korea; (S.L.); (Y.S.); (Y.S.)
- Asan Medical Institute of Convergence Science and Technology, Asan Medical Center, Seoul 05505, Korea
| | - Kyunggon Kim
- Department of Convergence Medicine, Asan Medical Center, Seoul 05505, Korea;
| | - Youngsup Song
- Department of Biomedical Sciences, University of Ulsan College of Medicine, Seoul 138-736, Korea; (S.L.); (Y.S.); (Y.S.)
- Asan Medical Institute of Convergence Science and Technology, Asan Medical Center, Seoul 05505, Korea
| | - Yongsub Kim
- Department of Biomedical Sciences, University of Ulsan College of Medicine, Seoul 138-736, Korea; (S.L.); (Y.S.); (Y.S.)
- Asan Medical Institute of Convergence Science and Technology, Asan Medical Center, Seoul 05505, Korea
| | - Sang-Wook Kang
- Department of Biomedical Sciences, University of Ulsan College of Medicine, Seoul 138-736, Korea; (S.L.); (Y.S.); (Y.S.)
- Asan Medical Institute of Convergence Science and Technology, Asan Medical Center, Seoul 05505, Korea
- Correspondence: ; Tel.: +82-2-3010-2205
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Abstract
The endoplasmic reticulum (ER) translocon complex is the main gate into the secretory pathway, facilitating the translocation of nascent peptides into the ER lumen or their integration into the lipid membrane. Protein biogenesis in the ER involves additional processes, many of them occurring co-translationally while the nascent protein resides at the translocon complex, including recruitment of ER-targeted ribosome-nascent-chain complexes, glycosylation, signal peptide cleavage, membrane protein topogenesis and folding. To perform such varied functions on a broad range of substrates, the ER translocon complex has different accessory components that associate with it either stably or transiently. Here, we review recent structural and functional insights into this dynamically constituted central hub in the ER and its components. Recent cryo-electron microscopy (EM) studies have dissected the molecular organization of the co-translational ER translocon complex, comprising the Sec61 protein-conducting channel, the translocon-associated protein complex and the oligosaccharyl transferase complex. Complemented by structural characterization of the post-translational import machinery, key molecular principles emerge that distinguish co- and post-translational protein import and biogenesis. Further cryo-EM structures promise to expand our mechanistic understanding of the various biochemical functions involving protein biogenesis and quality control in the ER.
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Affiliation(s)
- Max Gemmer
- Cryo-Electron Microscopy, Bijvoet Center for Biomolecular Research, Utrecht University, 3584 CH Utrecht, The Netherlands
| | - Friedrich Förster
- Cryo-Electron Microscopy, Bijvoet Center for Biomolecular Research, Utrecht University, 3584 CH Utrecht, The Netherlands
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25
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Abstract
Due to the heterogenous lipid environment in which integral membrane proteins are embedded, they should follow a set of assembly rules, which govern transmembrane protein folding and topogenesis accordingly to a given lipid profile. Recombinant strains of bacteria have been engineered to have different membrane phospholipid compositions by molecular genetic manipulation of endogenous and foreign genes encoding lipid biosynthetic enzymes. Such strains provide a means to investigate the in vivo role of lipids in many different aspects of membrane function, folding and biogenesis. In vitro and in vivo studies established a function of lipids as molecular chaperones and topological determinants specifically assisting folding and topogenesis of membrane proteins. These results led to the extension of the Positive Inside Rule to Charge Balance Rule, which incorporates a role for lipid-protein interactions in determining membrane protein topological organization at the time of initial membrane insertion and dynamically after initial assembly. Membrane protein topogenesis appears to be a thermodynamically driven process in which lipid-protein interactions affect the potency of charged amino acid residues as topological signals. Dual topology for a membrane protein can be established during initial assembly where folding intermediates in multiple topological conformations are in rapid equilibrium (thus separated by a low activation energy), which is determined by the lipid environment. Post-assembly changes in lipid composition or post-translational modifications can trigger a reorganization of protein topology by inducing destabilization and refolding of a membrane protein. The lipid-dependent dynamic nature of membrane protein organization provides a novel means of regulating protein function.
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26
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Abstract
To identify the translocation components in cells, and to understand how they function in protein transport and membrane insertion, a variety of techniques have been used such as genetics, biochemistry, structural biology and single molecule methods. In particular, site-directed crosslinking between the client proteins and components of the translocation machineries have contributed significantly in the past and will do so in the future. One advantage of this technology is that it can be applied in vivo as well as in vitro and a comparison of the two approaches can be made. Also, the in vivo techniques allow time-dependent protocols which are essential for studying cellular pathways. Protein purification and reconstitution into proteoliposomes are the gold standard for studying membrane-based transport and translocation systems. With these biochemically defined approaches the function of each component in protein transport can be addressed individually with a plethora of biophysical techniques. Recently, the use of nanodiscs for reconstitution has added another extension of this reductionistic approach. Fluorescence based studies, cryo-microscopy and NMR spectroscopy have significantly added to our understanding how proteins move into and across membranes and will do this also in future.
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Affiliation(s)
- Andreas Kuhn
- Institute of Microbiology and Molecular Biology, University of Hohenheim, 70599, Stuttgart, Germany.
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27
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Marinko J, Huang H, Penn WD, Capra JA, Schlebach JP, Sanders CR. Folding and Misfolding of Human Membrane Proteins in Health and Disease: From Single Molecules to Cellular Proteostasis. Chem Rev 2019; 119:5537-5606. [PMID: 30608666 PMCID: PMC6506414 DOI: 10.1021/acs.chemrev.8b00532] [Citation(s) in RCA: 153] [Impact Index Per Article: 30.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2018] [Indexed: 12/13/2022]
Abstract
Advances over the past 25 years have revealed much about how the structural properties of membranes and associated proteins are linked to the thermodynamics and kinetics of membrane protein (MP) folding. At the same time biochemical progress has outlined how cellular proteostasis networks mediate MP folding and manage misfolding in the cell. When combined with results from genomic sequencing, these studies have established paradigms for how MP folding and misfolding are linked to the molecular etiologies of a variety of diseases. This emerging framework has paved the way for the development of a new class of small molecule "pharmacological chaperones" that bind to and stabilize misfolded MP variants, some of which are now in clinical use. In this review, we comprehensively outline current perspectives on the folding and misfolding of integral MPs as well as the mechanisms of cellular MP quality control. Based on these perspectives, we highlight new opportunities for innovations that bridge our molecular understanding of the energetics of MP folding with the nuanced complexity of biological systems. Given the many linkages between MP misfolding and human disease, we also examine some of the exciting opportunities to leverage these advances to address emerging challenges in the development of therapeutics and precision medicine.
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Affiliation(s)
- Justin
T. Marinko
- Department
of Biochemistry, Vanderbilt University, Nashville, Tennessee 37240, United States
- Center
for Structural Biology, Vanderbilt University, Nashville, Tennessee 37240, United States
| | - Hui Huang
- Department
of Biochemistry, Vanderbilt University, Nashville, Tennessee 37240, United States
- Center
for Structural Biology, Vanderbilt University, Nashville, Tennessee 37240, United States
| | - Wesley D. Penn
- Department
of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - John A. Capra
- Center
for Structural Biology, Vanderbilt University, Nashville, Tennessee 37240, United States
- Department
of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37245, United States
| | - Jonathan P. Schlebach
- Department
of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Charles R. Sanders
- Department
of Biochemistry, Vanderbilt University, Nashville, Tennessee 37240, United States
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Spiess M, Junne T, Janoschke M. Membrane Protein Integration and Topogenesis at the ER. Protein J 2019; 38:306-316. [DOI: 10.1007/s10930-019-09827-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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29
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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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30
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Nguyen D, Stutz R, Schorr S, Lang S, Pfeffer S, Freeze HH, Förster F, Helms V, Dudek J, Zimmermann R. Proteomics reveals signal peptide features determining the client specificity in human TRAP-dependent ER protein import. Nat Commun 2018; 9:3765. [PMID: 30217974 PMCID: PMC6138672 DOI: 10.1038/s41467-018-06188-z] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Accepted: 08/23/2018] [Indexed: 12/22/2022] Open
Abstract
In mammalian cells, one-third of all polypeptides are transported into or across the ER membrane via the Sec61 channel. While the Sec61 complex facilitates translocation of all polypeptides with amino-terminal signal peptides (SP) or transmembrane helices, the Sec61-auxiliary translocon-associated protein (TRAP) complex supports translocation of only a subset of precursors. To characterize determinants of TRAP substrate specificity, we here systematically identify TRAP-dependent precursors by analyzing cellular protein abundance changes upon TRAP depletion using quantitative label-free proteomics. The results are validated in independent experiments by western blotting, quantitative RT-PCR, and complementation analysis. The SPs of TRAP clients exhibit above-average glycine-plus-proline content and below-average hydrophobicity as distinguishing features. Thus, TRAP may act as SP receptor on the ER membrane’s cytosolic face, recognizing precursor polypeptides with SPs of high glycine-plus-proline content and/or low hydrophobicity, and triggering substrate-specific opening of the Sec61 channel through interactions with the ER-lumenal hinge of Sec61α. While Sec61 enables ER import of all polypeptides with N-terminal signal peptides, only selected clients are accepted for TRAP-assisted ER import. Here, the authors use a proteomics approach to characterize TRAP-dependent clients, identifying signal peptide features that govern recognition by TRAP.
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Affiliation(s)
- Duy Nguyen
- Center for Bioinformatics, Saarland University, 66041, Saarbrücken, Germany
| | - Regine Stutz
- Medical Biochemistry and Molecular Biology, Saarland University, 66421, Homburg, Germany
| | - Stefan Schorr
- Medical Biochemistry and Molecular Biology, Saarland University, 66421, Homburg, Germany
| | - Sven Lang
- Medical Biochemistry and Molecular Biology, Saarland University, 66421, Homburg, Germany
| | - Stefan Pfeffer
- Max-Planck Institute of Biochemistry, Department of Molecular Structural Biology, 82152, Martinsried, Germany
| | - Hudson H Freeze
- Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, CA, 92037, USA
| | - Friedrich Förster
- Bijvoet Center for Biomolecular Research, Utrecht University, 3584, CH, Utrecht, The Netherlands
| | - Volkhard Helms
- Center for Bioinformatics, Saarland University, 66041, Saarbrücken, Germany.
| | - Johanna Dudek
- Medical Biochemistry and Molecular Biology, Saarland University, 66421, Homburg, Germany.
| | - Richard Zimmermann
- Medical Biochemistry and Molecular Biology, Saarland University, 66421, Homburg, Germany.
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31
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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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Pfeffer S, Dudek J, Schaffer M, Ng BG, Albert S, Plitzko JM, Baumeister W, Zimmermann R, Freeze HH, Engel BD, Förster F. Dissecting the molecular organization of the translocon-associated protein complex. Nat Commun 2017; 8:14516. [PMID: 28218252 PMCID: PMC5321747 DOI: 10.1038/ncomms14516] [Citation(s) in RCA: 102] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 01/05/2017] [Indexed: 12/26/2022] Open
Abstract
In eukaryotic cells, one-third of all proteins must be transported across or inserted into the endoplasmic reticulum (ER) membrane by the ER protein translocon. The translocon-associated protein (TRAP) complex is an integral component of the translocon, assisting the Sec61 protein-conducting channel by regulating signal sequence and transmembrane helix insertion in a substrate-dependent manner. Here we use cryo-electron tomography (CET) to study the structure of the native translocon in evolutionarily divergent organisms and disease-linked TRAP mutant fibroblasts from human patients. The structural differences detected by subtomogram analysis form a basis for dissecting the molecular organization of the TRAP complex. We assign positions to the four TRAP subunits within the complex, providing insights into their individual functions. The revealed molecular architecture of a central translocon component advances our understanding of membrane protein biogenesis and sheds light on the role of TRAP in human congenital disorders of glycosylation.
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Affiliation(s)
- Stefan Pfeffer
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Johanna Dudek
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Building 44, 66421 Homburg, Germany
| | - Miroslava Schaffer
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Bobby G Ng
- Human Genetics Program, Sanford Burnham Prebys Medical Discovery Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Sahradha Albert
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Jürgen M Plitzko
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Wolfgang Baumeister
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Richard Zimmermann
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Building 44, 66421 Homburg, Germany
| | - Hudson H Freeze
- Human Genetics Program, Sanford Burnham Prebys Medical Discovery Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Benjamin D Engel
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Friedrich Förster
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.,Cryo-Electron Microscopy, Bijvoet Center for Biomolecular Research, Department of Chemistry, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
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33
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Bañó-Polo M, Martínez-Garay CA, Grau B, Martínez-Gil L, Mingarro I. Membrane insertion and topology of the translocon-associated protein (TRAP) gamma subunit. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:903-909. [PMID: 28132902 DOI: 10.1016/j.bbamem.2017.01.027] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Revised: 01/19/2017] [Accepted: 01/25/2017] [Indexed: 12/20/2022]
Abstract
Translocon-associated protein (TRAP) complex is intimately associated with the ER translocon for the insertion or translocation of newly synthesised proteins in eukaryotic cells. The TRAP complex is comprised of three single-spanning and one multiple-spanning subunits. We have investigated the membrane insertion and topology of the multiple-spanning TRAP-γ subunit by glycosylation mapping and green fluorescent protein fusions both in vitro and in cell cultures. Results demonstrate that TRAP-γ has four transmembrane (TM) segments, an Nt/Ct cytosolic orientation and that the less hydrophobic TM segment inserts efficiently into the membrane only in the cellular context of full-length protein.
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Affiliation(s)
- Manuel Bañó-Polo
- Departament de Bioquímica i Biologia Molecular, Estructura de Recerca Interdisciplinar en Biotecnologia i Biomedicina (ERI BioTecMed), Universitat de València, E-46 100 Burjassot, Spain
| | - Carlos A Martínez-Garay
- Departament de Bioquímica i Biologia Molecular, Estructura de Recerca Interdisciplinar en Biotecnologia i Biomedicina (ERI BioTecMed), Universitat de València, E-46 100 Burjassot, Spain
| | - Brayan Grau
- Departament de Bioquímica i Biologia Molecular, Estructura de Recerca Interdisciplinar en Biotecnologia i Biomedicina (ERI BioTecMed), Universitat de València, E-46 100 Burjassot, Spain
| | - Luis Martínez-Gil
- Departament de Bioquímica i Biologia Molecular, Estructura de Recerca Interdisciplinar en Biotecnologia i Biomedicina (ERI BioTecMed), Universitat de València, E-46 100 Burjassot, Spain
| | - Ismael Mingarro
- Departament de Bioquímica i Biologia Molecular, Estructura de Recerca Interdisciplinar en Biotecnologia i Biomedicina (ERI BioTecMed), Universitat de València, E-46 100 Burjassot, Spain.
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Przybylla S, Stindt J, Kleinschrodt D, Schulte am Esch J, Häussinger D, Keitel V, Smits SH, Schmitt L. Analysis of the Bile Salt Export Pump (ABCB11) Interactome Employing Complementary Approaches. PLoS One 2016; 11:e0159778. [PMID: 27472061 PMCID: PMC4966956 DOI: 10.1371/journal.pone.0159778] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 06/11/2016] [Indexed: 12/12/2022] Open
Abstract
The bile salt export pump (BSEP, ABCB11) plays an essential role in the formation of bile. In hepatocytes, BSEP is localized within the apical (canalicular) membrane and a deficiency of canalicular BSEP function is associated with severe forms of cholestasis. Regulation of correct trafficking to the canalicular membrane and of activity is essential to ensure BSEP functionality and thus normal bile flow. However, little is known about the identity of interaction partners regulating function and localization of BSEP. In our study, interaction partners of BSEP were identified in a complementary approach: Firstly, BSEP interaction partners were co-immunoprecipitated from human liver samples and identified by mass spectrometry (MS). Secondly, a membrane yeast two-hybrid (MYTH) assay was used to determine protein interaction partners using a human liver cDNA library. A selection of interaction partners identified both by MYTH and MS were verified by in vitro interaction studies using purified proteins. By these complementary approaches, a set of ten novel BSEP interaction partners was identified. With the exception of radixin, all other interaction partners were integral or membrane-associated proteins including proteins of the early secretory pathway and the bile acyl-CoA synthetase, the second to last, ER-associated enzyme of bile salt synthesis.
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Affiliation(s)
- Susanne Przybylla
- Institute of Biochemistry, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany
| | - Jan Stindt
- Department of Gastroenterology, Hepatology and Infectious Diseases, University Hospital, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany
| | - Diana Kleinschrodt
- Institute of Biochemistry, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany
| | - Jan Schulte am Esch
- Department of General, Visceral and Pediatric Surgery, University Hospital, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Dieter Häussinger
- Department of Gastroenterology, Hepatology and Infectious Diseases, University Hospital, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany
| | - Verena Keitel
- Department of Gastroenterology, Hepatology and Infectious Diseases, University Hospital, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany
| | - Sander H. Smits
- Institute of Biochemistry, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany
| | - Lutz Schmitt
- Institute of Biochemistry, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany
- * E-mail:
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35
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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: 38] [Impact Index Per Article: 4.8] [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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36
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Garg B, Pathria G, Wagner C, Maurer M, Wagner SN. Signal Sequence Receptor 2 is required for survival of human melanoma cells as part of an unfolded protein response to endoplasmic reticulum stress. Mutagenesis 2016; 31:573-82. [PMID: 27180333 DOI: 10.1093/mutage/gew023] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Current therapy approaches in melanoma targeting have met with the development of resistance and tumour recurrence with a more aggressive phenotype. In a quest for alternative therapy targets, we had previously identified Signal Sequence Receptor 2 (SSR2) as a gene with high expression in a subgroup of human primary melanomas. Now we show that SSR2 exerts a prosurvival functionality in human melanoma cells and that high expression levels of SSR2 are associated with an unfavourable disease outcome in primary melanoma patients. Consistent with SSR's role in translocation of proteins from the ribosome across the endoplasmic reticulum (ER) membrane, our data supports induction of SSR2 as a part of the ER stress response. This response included SSR2 upregulation upon development of therapy resistance to BRAF inhibitors, as well as the dependency of cell survival of BRAF inhibitor-resistant melanoma cells on SSR2. Complementary gain and loss of function data showed the Unfolded Protein Response (UPR) to ER stress as an inducer of SSR2 via transcriptional regulation through X-Box Binding Protein 1s (XBP1s) and support an ER stress-UPR-Transcription Factor XBP1s-SSR2 response axis in human melanocytic cells. Together with its dispensability for survival in normal human cells, these data propose SSR2 as a potential therapeutic target in (therapy-resistant) human melanoma.
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Affiliation(s)
- Bhavuk Garg
- Division of Immunology Allergy and Infectious Diseases (DIAID), Department of Dermatology, Medical University of Vienna, Waehringer Guertel 18-20, Vienna A-1090, Austria
| | - Gaurav Pathria
- Division of Immunology Allergy and Infectious Diseases (DIAID), Department of Dermatology, Medical University of Vienna, Waehringer Guertel 18-20, Vienna A-1090, Austria, Present address: Biochemical-Pharmacological Center, University of Marburg, Karl-von-Frisch-Straße, Marburg 35032, Germany
| | - Christine Wagner
- Division of Immunology Allergy and Infectious Diseases (DIAID), Department of Dermatology, Medical University of Vienna, Waehringer Guertel 18-20, Vienna A-1090, Austria
| | - Margarita Maurer
- Division of Immunology Allergy and Infectious Diseases (DIAID), Department of Dermatology, Medical University of Vienna, Waehringer Guertel 18-20, Vienna A-1090, Austria
| | - Stephan N Wagner
- Division of Immunology Allergy and Infectious Diseases (DIAID), Department of Dermatology, Medical University of Vienna, Waehringer Guertel 18-20, Vienna A-1090, Austria,
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Zimmermann R. Components and Mechanisms of Import, Modification, Folding, and Assembly of Immunoglobulins in the Endoplasmic Reticulum. J Clin Immunol 2016; 36 Suppl 1:5-11. [PMID: 26923573 DOI: 10.1007/s10875-016-0250-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Accepted: 02/19/2016] [Indexed: 11/27/2022]
Abstract
In mammalian cells, the endoplasmic reticulum (ER) plays a central role in biogenesis of secretory- and plasma membrane proteins as well as in cellular calcium (Ca(2+)) homeostasis. The protein biogenesis function involves an aqueous polypeptide conducting channel in the ER membrane, which is formed by the heterotrimeric Sec61 complex; the store- and receptor-controlled Ca(2+)- release function requires a steep ER to cytosol gradient, with more than 500 μM free Ca(2+) in the ER and 50 nM Ca(2+) in the cytosol. Recent work demonstrated that the Sec61 complex can transiently allow passive ER Ca(2+) efflux. Therefore, gating of the Sec61 channel has to be tightly regulated by substrates as well as allosteric effectors. The ER lumenal Hsp70-type molecular chaperone, immunoglobulin heavy-chain binding protein (BiP), together with its membrane resident co-chaperone Sec63 facilitates channel opening in a precursor specific manner. In addition, BiP, together with its lumenal co-chaperones, ERj3 and ERj6, as well as cytosolic Ca(2+)-calmodulin (CaM) in collaboration with the membrane resident Sec62 protein represent allosteric effectors for channel closure. In the course of the last couple of years several human diseases were linked to the Sec61 complex and its effectors and were termed Sec61-channelopathies.
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Affiliation(s)
- Richard Zimmermann
- Competence Center for Molecular Medicine, Saarland University Medical School, Building 44, D-66421, Homburg, Germany.
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38
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Van Lehn RC, Zhang B, Miller TF. Regulation of multispanning membrane protein topology via post-translational annealing. eLife 2015; 4. [PMID: 26408961 PMCID: PMC4635508 DOI: 10.7554/elife.08697] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Accepted: 09/25/2015] [Indexed: 12/19/2022] Open
Abstract
The canonical mechanism for multispanning membrane protein topogenesis suggests that protein topology is established during cotranslational membrane integration. However, this mechanism is inconsistent with the behavior of EmrE, a dual-topology protein for which the mutation of positively charged loop residues, even close to the C-terminus, leads to dramatic shifts in its topology. We use coarse-grained simulations to investigate the Sec-facilitated membrane integration of EmrE and its mutants on realistic biological timescales. This work reveals a mechanism for regulating membrane-protein topogenesis, in which initially misintegrated configurations of the proteins undergo post-translational annealing to reach fully integrated multispanning topologies. The energetic barriers associated with this post-translational annealing process enforce kinetic pathways that dictate the topology of the fully integrated proteins. The proposed mechanism agrees well with the experimentally observed features of EmrE topogenesis and provides a range of experimentally testable predictions regarding the effect of translocon mutations on membrane protein topogenesis. DOI:http://dx.doi.org/10.7554/eLife.08697.001 Proteins are long chains of smaller molecules called amino acids, and are built inside cells by a molecular machine called the ribosome. Many important proteins must be inserted into the membrane that surrounds each cell in order to carry out their role. As these proteins are being built by the ribosome, they thread their way into a membrane-spanning channel (called the translocon) from the inner side of the membrane. Short segments of these integral membrane proteins (called transmembrane domains) then become embedded in the membrane, while other parts of the protein remain on either side of the membrane. For a membrane protein to work properly, the end of each of its transmembrane domains must be on the correct side of the membrane (i.e., the protein must obtain the correct ‘topology’). The conventional model for this process suggests that topology is fixed when the first transmembrane domain of a protein is initially integrated into the membrane, while the ribosome is still building the protein. This model can explain most integral membrane proteins, which only have a single topology. However, it cannot explain the family of membrane proteins that have an almost equal chance of adopting one of two different topologies (so-called ‘dual-topology proteins’). Van Lehn et al. have now used computer modeling to simulate how a bacterial protein called EmrE (which is a dual-topology protein) integrates into the membrane via the translocon. The results reveal that a few transmembrane domains in EmrE do not fully integrate into the membrane while the ribosome is building the protein. Instead, these transmembrane domains slowly integrate after the ribosome has finished its job. These findings contradict the conventional model and suggest that some membrane proteins only become fully integrated after the protein-building process is complete. The next step in this work is to experimentally test predictions from the computer simulations. DOI:http://dx.doi.org/10.7554/eLife.08697.002
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Affiliation(s)
- Reid C Van Lehn
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, United States
| | - Bin Zhang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, United States
| | - Thomas F Miller
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, United States
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Ng BG, Raymond K, Kircher M, Buckingham KJ, Wood T, Shendure J, Nickerson DA, Bamshad MJ, Wong JTS, Monteiro FP, Graham BH, Jackson S, Sparkes R, Scheuerle AE, Cathey S, Kok F, Gibson JB, Freeze HH. Expanding the Molecular and Clinical Phenotype of SSR4-CDG. Hum Mutat 2015; 36:1048-51. [PMID: 26264460 DOI: 10.1002/humu.22856] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Accepted: 08/02/2015] [Indexed: 01/16/2023]
Abstract
Congenital disorders of glycosylation (CDG) are a group of mostly autosomal recessive disorders primarily characterized by neurological abnormalities. Recently, we described a single CDG patient with a de novo mutation in the X-linked gene, Signal Sequence Receptor 4 (SSR4). We performed whole-exome sequencing to identify causal variants in several affected individuals who had either an undifferentiated neurological disorder or unsolved CDG of unknown etiology based on abnormal transferrin glycosylation. We now report eight affected males with either de novo (4) or inherited (4) loss of function mutations in SSR4. Western blot analysis revealed that the mutations caused a complete loss of SSR4 protein. In nearly all cases, the abnormal glycosylation of serum transferrin was only slightly above the accepted normal cutoff range.
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Affiliation(s)
- Bobby G Ng
- Human Genetics Program, Sanford - Burnham - Prebys Medical Discovery Institute, La Jolla, California
| | - Kimiyo Raymond
- Biochemical Genetics Laboratory, Mayo Clinic College of Medicine, Rochester, Minnesota
| | - Martin Kircher
- Department of Genome Sciences, University of Washington, Seattle, Washington
| | - Kati J Buckingham
- Department of Pediatrics, University of Washington, Seattle, Washington
| | - Tim Wood
- Department of Clinical Genetics, Greenwood Genetic Center, Charleston Office, North Charleston, South Caroline
| | - Jay Shendure
- Department of Genome Sciences, University of Washington, Seattle, Washington
| | - Deborah A Nickerson
- Department of Genome Sciences, University of Washington, Seattle, Washington
| | - Michael J Bamshad
- Department of Genome Sciences, University of Washington, Seattle, Washington.,Department of Pediatrics, University of Washington, Seattle, Washington
| | | | - Jonathan T S Wong
- Human Genetics Program, Sanford - Burnham - Prebys Medical Discovery Institute, La Jolla, California
| | - Fabiola Paoli Monteiro
- Department of Medical Genetics, University of Campinas (UNICAMP), São Paulo, Brazil.,Mendelics Genomic Analysis, São Paulo, São Paulo, Brazil
| | - Brett H Graham
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas
| | - Sheryl Jackson
- Department of Medical Genetics, University of Calgary, Calgary, AB, Canada
| | - Rebecca Sparkes
- Department of Medical Genetics, University of Calgary, Calgary, AB, Canada
| | - Angela E Scheuerle
- Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Sara Cathey
- Department of Clinical Genetics, Greenwood Genetic Center, Charleston Office, North Charleston, South Caroline
| | - Fernando Kok
- Mendelics Genomic Analysis, São Paulo, São Paulo, Brazil.,Department of Neurology, University of São Paulo, São Paulo, Brazil
| | - James B Gibson
- Clinical and Metabolic Genetics, Specially for Children, Austin, Texas
| | - Hudson H Freeze
- Human Genetics Program, Sanford - Burnham - Prebys Medical Discovery Institute, La Jolla, California
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40
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Mulcahy MJ, Blattman SB, Barrantes FJ, Lukas RJ, Hawrot E. Resistance to Inhibitors of Cholinesterase 3 (Ric-3) Expression Promotes Selective Protein Associations with the Human α7-Nicotinic Acetylcholine Receptor Interactome. PLoS One 2015; 10:e0134409. [PMID: 26258666 PMCID: PMC4530945 DOI: 10.1371/journal.pone.0134409] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Accepted: 07/08/2015] [Indexed: 11/19/2022] Open
Abstract
The α7-nicotinic acetylcholine receptor (α7-nAChR) is a ligand-gated ion channel widely expressed in vertebrates and is associated with numerous physiological functions. As transmembrane ion channels, α7-nAChRs need to be expressed on the surface of the plasma membrane to function. The receptor has been reported to associate with proteins involved with receptor biogenesis, modulation of receptor properties, as well as intracellular signaling cascades and some of these associated proteins may affect surface expression of α7-nAChRs. The putative chaperone resistance to inhibitors of cholinesterase 3 (Ric-3) has been reported to interact with, and enhance the surface expression of, α7-nAChRs. In this study, we identified proteins that associate with α7-nAChRs when Ric-3 is expressed. Using α-bungarotoxin (α-bgtx), we isolated and compared α7-nAChR-associated proteins from two stably transfected, human tumor-derived cell lines: SH-EP1-hα7 expressing human α7-nAChRs and the same cell line further transfected to express Ric-3, SH-EP1-hα7-Ric-3. Mass spectrometric analysis of peptides identified thirty-nine proteins that are associated with α7-nAChRs only when Ric-3 was expressed. Significantly, and consistent with reports of Ric-3 function in the literature, several of the identified proteins are involved in biological processes that may affect nAChR surface expression such as post-translational processing of proteins, protein trafficking, and protein transport. Additionally, proteins affecting the cell cycle, the cytoskeleton, stress responses, as well as cyclic AMP- and inositol triphosphate-dependent signaling cascades were identified. These results illuminate how α-bgtx may be used to isolate and identify α7-nAChRs as well as how the expression of chaperones such as Ric-3 can influence proteins associating with α7-nAChRs. These associating proteins may alter activities of α7-nAChRs to expand their functionally-relevant repertoire as well as to affect biogenesis and membrane trafficking of α7-nAChRs.
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Affiliation(s)
- Matthew J. Mulcahy
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island, United States of America
| | - Sydney B. Blattman
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island, United States of America
| | - Francisco J. Barrantes
- Laboratory of Molecular Neurobiology, Institute of Biomedical Research, UCA-CONICET, Buenos Aires, Argentina
| | - Ronald J. Lukas
- Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona, United States of America
| | - Edward Hawrot
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island, United States of America
- * E-mail:
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41
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De Marothy MT, Elofsson A. Marginally hydrophobic transmembrane α-helices shaping membrane protein folding. Protein Sci 2015; 24:1057-74. [PMID: 25970811 DOI: 10.1002/pro.2698] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 04/24/2015] [Indexed: 01/12/2023]
Abstract
Cells have developed an incredible machinery to facilitate the insertion of membrane proteins into the membrane. While we have a fairly good understanding of the mechanism and determinants of membrane integration, more data is needed to understand the insertion of membrane proteins with more complex insertion and folding pathways. This review will focus on marginally hydrophobic transmembrane helices and their influence on membrane protein folding. These weakly hydrophobic transmembrane segments are by themselves not recognized by the translocon and therefore rely on local sequence context for membrane integration. How can such segments reside within the membrane? We will discuss this in the light of features found in the protein itself as well as the environment it resides in. Several characteristics in proteins have been described to influence the insertion of marginally hydrophobic helices. Additionally, the influence of biological membranes is significant. To begin with, the actual cost for having polar groups within the membrane may not be as high as expected; the presence of proteins in the membrane as well as characteristics of some amino acids may enable a transmembrane helix to harbor a charged residue. The lipid environment has also been shown to directly influence the topology as well as membrane boundaries of transmembrane helices-implying a dynamic relationship between membrane proteins and their environment.
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Affiliation(s)
- Minttu T De Marothy
- Department of Biochemistry and Biophysics Science for Life Laboratory, Stockholm University, Solna, SE-171 21, Sweden
| | - Arne Elofsson
- Department of Biochemistry and Biophysics Science for Life Laboratory, Stockholm University, Solna, SE-171 21, Sweden
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42
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Conti BJ, Devaraneni PK, Yang Z, David LL, Skach WR. Cotranslational stabilization of Sec62/63 within the ER Sec61 translocon is controlled by distinct substrate-driven translocation events. Mol Cell 2015; 58:269-83. [PMID: 25801167 DOI: 10.1016/j.molcel.2015.02.018] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Revised: 01/08/2015] [Accepted: 02/10/2015] [Indexed: 01/19/2023]
Abstract
The ER Sec61 translocon is a large macromolecular machine responsible for partitioning secretory and membrane polypeptides into the lumen, cytosol, and lipid bilayer. Because the Sec61 protein-conducting channel has been isolated in multiple membrane-derived complexes, we determined how the nascent polypeptide modulates translocon component associations during defined cotranslational translocation events. The model substrate preprolactin (pPL) was isolated principally with Sec61αβγ upon membrane targeting, whereas higher-order complexes containing OST, TRAP, and TRAM were stabilized following substrate translocation. Blocking pPL translocation by passenger domain folding favored stabilization of an alternate complex that contained Sec61, Sec62, and Sec63. Moreover, Sec62/63 stabilization within the translocon occurred for native endogenous substrates, such as the prion protein, and correlated with a delay in translocation initiation. These data show that cotranslational translocon contacts are ultimately controlled by the engaged nascent chain and the resultant substrate-driven translocation events.
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Affiliation(s)
- Brian J Conti
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, OR 97239, USA.
| | - Prasanna K Devaraneni
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, OR 97239, USA
| | - Zhongying Yang
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, OR 97239, USA
| | - Larry L David
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, OR 97239, USA
| | - William R Skach
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, OR 97239, USA; Cystic Fibrosis Foundation Therapeutics, Inc., Bethesda, MD 20814, USA
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43
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Pawlak A, Strzadala L, Kalas W. Non-genomic effects of the NR4A1/Nur77/TR3/NGFIB orphan nuclear receptor. Steroids 2015; 95:1-6. [PMID: 25555471 DOI: 10.1016/j.steroids.2014.12.020] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Revised: 10/07/2014] [Accepted: 12/18/2014] [Indexed: 11/30/2022]
Abstract
The orphan nuclear receptor NR4A1/Nur77/TR3/NGFIB acts primarily as a transcription factor to regulate the expression of multiple genes. However, increasing research attention has recently been given to non-genomic activities of NR4A1. The first description of a non-genomic action of NR4A1 referred to the conversion of anti-apoptotic Bcl-2 into a pro-apoptotic protein by direct interaction with NR4A1. In response to certain apoptotic stimuli, NR4A1 translocates from the nucleus to the mitochondrial outer membrane (MOM) where it associates with Bcl-2 and thereby causes apoptosis. Afterwards, it appeared that NR4A1 could also bind and convert other anti-apoptotic Bcl-2 family members. The latest studies indicate a significant role of NR4A1 in the process of autophagy. For example, a new NR4A1-mediated pathway specific for melanoma cells has been described where NR4A1 interacts with the adenine nucleotide translocase 1 (ANT1) on the mitochondrial inner membrane (MIM) leading to induction of the autophagy pathway. Moreover, NR4A1 interaction with cytoplasmic p53 may also contribute to the induction of autophagy. In addition to mitochondria, NR4A1 could be translocated to the outer membrane of the endoplasmic reticulum (ER) and associate with Bcl-2 or translocon-associated protein subunit γ (TRAPγ) causing ER stress-induced apoptosis. NR4A1 also contributes to the proteasomal degradation of β-catenin in colon cancer cells in vitro and in vivo, as well as to the stabilization of hypoxia-inducible factor-1α (HIF-1α) under non-hypoxic conditions. This review summarizes research findings on non-genomic effects of NR4A1 in normal and cancer cells.
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Affiliation(s)
- Alicja Pawlak
- Ludwik Hirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, Rudolfa Weigla 12, 53-114 Wroclaw, Poland.
| | - Leon Strzadala
- Ludwik Hirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, Rudolfa Weigla 12, 53-114 Wroclaw, Poland.
| | - Wojciech Kalas
- Ludwik Hirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, Rudolfa Weigla 12, 53-114 Wroclaw, Poland; Jan Dlugosz University in Czestochowa, Waszyngtona 4/8, 42-200 Czestochowa, Poland.
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44
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Rutz C, Klein W, Schülein R. N-Terminal Signal Peptides of G Protein-Coupled Receptors. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2015; 132:267-87. [DOI: 10.1016/bs.pmbts.2015.03.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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45
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Dou D, da Silva DV, Nordholm J, Wang H, Daniels R. Type II transmembrane domain hydrophobicity dictates the cotranslational dependence for inversion. Mol Biol Cell 2014; 25:3363-74. [PMID: 25165139 PMCID: PMC4214783 DOI: 10.1091/mbc.e14-04-0874] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The cellular hydrophobicity threshold for the inversion of Sec-dependent Nin-Cout (type II) transmembrane domains is dictated by whether their membrane integration occurs cotranslationally or posttranslationally. Membrane insertion by the Sec61 translocon in the endoplasmic reticulum (ER) is highly dependent on hydrophobicity. This places stringent hydrophobicity requirements on transmembrane domains (TMDs) from single-spanning membrane proteins. On examining the single-spanning influenza A membrane proteins, we found that the strict hydrophobicity requirement applies to the Nout-Cin HA and M2 TMDs but not the Nin-Cout TMDs from the type II membrane protein neuraminidase (NA). To investigate this discrepancy, we analyzed NA TMDs of varying hydrophobicity, followed by increasing polypeptide lengths, in mammalian cells and ER microsomes. Our results show that the marginally hydrophobic NA TMDs (ΔGapp > 0 kcal/mol) require the cotranslational insertion process for facilitating their inversion during translocation and a positively charged N-terminal flanking residue and that NA inversion enhances its plasma membrane localization. Overall the cotranslational inversion of marginally hydrophobic NA TMDs initiates once ∼70 amino acids past the TMD are synthesized, and the efficiency reaches 50% by ∼100 amino acids, consistent with the positioning of this TMD class in type II human membrane proteins. Inversion of the M2 TMD, achieved by elongating its C-terminus, underscores the contribution of cotranslational synthesis to TMD inversion.
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Affiliation(s)
- Dan Dou
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University,
SE-106 91 Stockholm, Sweden
| | - Diogo V da Silva
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University,
SE-106 91 Stockholm, Sweden
| | - Johan Nordholm
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University,
SE-106 91 Stockholm, Sweden
| | - Hao Wang
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University,
SE-106 91 Stockholm, Sweden
| | - Robert Daniels
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University,
SE-106 91 Stockholm, Sweden
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46
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Jung SJ, Kim JEH, Reithinger JH, Kim H. The Sec62-Sec63 translocon facilitates translocation of the C-terminus of membrane proteins. J Cell Sci 2014; 127:4270-8. [PMID: 25097231 DOI: 10.1242/jcs.153650] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Sec62-Sec63 complex mediates post-translational translocation of a subset of primarily secretory proteins into the endoplasmic reticulum (ER) in yeast. Therefore, it has been thought that membrane proteins, which are mainly co-translationally targeted into the ER, are not handled by the Sec62-Sec63 translocon. By systematic analysis of single and multi-spanning membrane proteins with broad sequence context [with differing hydrophobicity, flanking charged residues and orientation of transmembrane (TM) segments], we show that mutations in the N-terminal cytosolic domain of yeast Sec62 impair its interaction with Sec63 and lead to defects in membrane insertion and translocation of the C-terminus of membrane proteins. These results suggest that there is an unappreciated function of the Sec62-Sec63 translocon in regulating topogenesis of membrane proteins in the eukaryotic cell.
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Affiliation(s)
- Sung-jun Jung
- School of Biological Sciences, Seoul National University, Seoul 151-747, South Korea
| | - Ji Eun Hani Kim
- School of Biological Sciences, Seoul National University, Seoul 151-747, South Korea
| | - Johannes H Reithinger
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Hyun Kim
- School of Biological Sciences, Seoul National University, Seoul 151-747, South Korea
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47
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Haßdenteufel S, Klein MC, Melnyk A, Zimmermann R. Protein transport into the human ER and related diseases, Sec61-channelopathies. Biochem Cell Biol 2014; 92:499-509. [PMID: 24934166 DOI: 10.1139/bcb-2014-0043] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Protein transport into the human endoplasmic reticulum (ER) is relevant to the biogenesis of most soluble and membrane proteins of organelles, which are involved in endo- or exo-cytsosis. It involves amino-terminal signal peptides in the precursor polypeptides and various transport components in the cytosol plus the ER, and can occur co- or post-translationally. The two mechanisms merge at the level of the ER membrane, specifically at the level of the heterotrimeric Sec61 complex, which forms a dynamic polypeptide-conducting channel in the ER membrane. Since the mammalian ER is also the main intracellular calcium storage organelle, and the Sec61 complex is calcium permeable, the Sec61 complex is tightly regulated in its equilibrium between the closed and open conformations, or "gated", by ligands, such as signal peptides of the transport substrates and the ER lumenal Hsp70-type molecular chaperone BiP. Furthermore, BiP binding to the incoming polypeptide contributes to the efficiency and unidirectionality of transport. Recent insights into the structure and dynamic equilibrium of the Sec61 complex have various mechanistic as well as medical implications.
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Affiliation(s)
- Sarah Haßdenteufel
- Medical Biochemistry & Molecular Biology, Saarland University, Building 44, Kirrbergerstr, D-66421 Homburg, Germany
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48
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Denks K, Vogt A, Sachelaru I, Petriman NA, Kudva R, Koch HG. The Sec translocon mediated protein transport in prokaryotes and eukaryotes. Mol Membr Biol 2014; 31:58-84. [DOI: 10.3109/09687688.2014.907455] [Citation(s) in RCA: 123] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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49
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Aviram N, Schuldiner M. Embracing the void--how much do we really know about targeting and translocation to the endoplasmic reticulum? Curr Opin Cell Biol 2014; 29:8-17. [PMID: 24662022 DOI: 10.1016/j.ceb.2014.02.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Revised: 02/22/2014] [Accepted: 02/24/2014] [Indexed: 11/28/2022]
Abstract
In order for a protein to enter the secretory pathway, two crucial steps must occur: it first needs to be targeted to the cytosolic surface of the endoplasmic reticulum (ER), and then be translocated across the ER membrane. Although for many years studies of targeting focused on the signal recognition particle, recent findings reveal that several alternative targeting pathways exist, some still undescribed, and some only recently elucidated. In addition, many genes implicated in the translocation step have not been assigned a specific function. Here, we will focus on the open questions regarding ER targeting and translocation, and discuss how combining classical biochemistry with systematic approaches can promote our understanding of these essential cellular steps.
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Affiliation(s)
- Naama Aviram
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel.
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