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Allen WJ, Collinson I. A unifying mechanism for protein transport through the core bacterial Sec machinery. Open Biol 2023; 13:230166. [PMID: 37643640 PMCID: PMC10465204 DOI: 10.1098/rsob.230166] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Accepted: 07/21/2023] [Indexed: 08/31/2023] Open
Abstract
Encapsulation and compartmentalization are fundamental to the evolution of cellular life, but they also pose a challenge: how to partition the molecules that perform biological functions-the proteins-across impermeable barriers into sub-cellular organelles, and to the outside. The solution lies in the evolution of specialized machines, translocons, found in every biological membrane, which act both as gate and gatekeeper across and into membrane bilayers. Understanding how these translocons operate at the molecular level has been a long-standing ambition of cell biology, and one that is approaching its denouement; particularly in the case of the ubiquitous Sec system. In this review, we highlight the fruits of recent game-changing technical innovations in structural biology, biophysics and biochemistry to present a largely complete mechanism for the bacterial version of the core Sec machinery. We discuss the merits of our model over alternative proposals and identify the remaining open questions. The template laid out by the study of the Sec system will be of immense value for probing the many other translocons found in diverse biological membranes, towards the ultimate goal of altering or impeding their functions for pharmaceutical or biotechnological purposes.
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Affiliation(s)
- William J. Allen
- School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK
| | - Ian Collinson
- School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK
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2
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Krishnamurthy S, Sardis MF, Eleftheriadis N, Chatzi KE, Smit JH, Karathanou K, Gouridis G, Portaliou AG, Bondar AN, Karamanou S, Economou A. Preproteins couple the intrinsic dynamics of SecA to its ATPase cycle to translocate via a catch and release mechanism. Cell Rep 2022; 38:110346. [PMID: 35139375 DOI: 10.1016/j.celrep.2022.110346] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 11/22/2021] [Accepted: 01/12/2022] [Indexed: 12/11/2022] Open
Abstract
Protein machines undergo conformational motions to interact with and manipulate polymeric substrates. The Sec translocase promiscuously recognizes, becomes activated, and secretes >500 non-folded preprotein clients across bacterial cytoplasmic membranes. Here, we reveal that the intrinsic dynamics of the translocase ATPase, SecA, and of preproteins combine to achieve translocation. SecA possesses an intrinsically dynamic preprotein clamp attached to an equally dynamic ATPase motor. Alternating motor conformations are finely controlled by the γ-phosphate of ATP, while ADP causes motor stalling, independently of clamp motions. Functional preproteins physically bridge these independent dynamics. Their signal peptides promote clamp closing; their mature domain overcomes the rate-limiting ADP release. While repeated ATP cycles shift the motor between unique states, multiple conformationally frustrated prongs in the clamp repeatedly "catch and release" trapped preprotein segments until translocation completion. This universal mechanism allows any preprotein to promiscuously recognize the translocase, usurp its intrinsic dynamics, and become secreted.
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Affiliation(s)
- Srinath Krishnamurthy
- KU Leuven, University of Leuven, Rega Institute, Department of Microbiology and Immunology, 3000 Leuven, Belgium
| | - Marios-Frantzeskos Sardis
- KU Leuven, University of Leuven, Rega Institute, Department of Microbiology and Immunology, 3000 Leuven, Belgium
| | - Nikolaos Eleftheriadis
- KU Leuven, University of Leuven, Rega Institute, Department of Microbiology and Immunology, 3000 Leuven, Belgium
| | - Katerina E Chatzi
- KU Leuven, University of Leuven, Rega Institute, Department of Microbiology and Immunology, 3000 Leuven, Belgium
| | - Jochem H Smit
- KU Leuven, University of Leuven, Rega Institute, Department of Microbiology and Immunology, 3000 Leuven, Belgium
| | - Konstantina Karathanou
- Freie Universität Berlin, Department of Physics, Theoretical Molecular Biophysics Group, Arnimallee 14, 14195 Berlin, Germany
| | - Giorgos Gouridis
- KU Leuven, University of Leuven, Rega Institute, Department of Microbiology and Immunology, 3000 Leuven, Belgium; Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, the Netherlands; Structural Biology Division, Institute of Molecular Biology and Biotechnology (IMBB-FORTH), Nikolaou Plastira 100, Heraklion, Crete, Greece
| | - Athina G Portaliou
- KU Leuven, University of Leuven, Rega Institute, Department of Microbiology and Immunology, 3000 Leuven, Belgium
| | - Ana-Nicoleta Bondar
- Freie Universität Berlin, Department of Physics, Theoretical Molecular Biophysics Group, Arnimallee 14, 14195 Berlin, Germany; University of Bucharest, Faculty of Physics, Atomiștilor 405, 077125 Măgurele, Romania; Forschungszentrum Jülich, Institute of Computational Biomedicine, IAS-5/INM-9, Wilhelm-Johnen Straße, 5428 Jülich, Germany
| | - Spyridoula Karamanou
- KU Leuven, University of Leuven, Rega Institute, Department of Microbiology and Immunology, 3000 Leuven, Belgium
| | - Anastassios Economou
- KU Leuven, University of Leuven, Rega Institute, Department of Microbiology and Immunology, 3000 Leuven, Belgium.
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Davis MM, Lamichhane R, Bruce BD. Elucidating Protein Translocon Dynamics with Single-Molecule Precision. Trends Cell Biol 2021; 31:569-583. [PMID: 33865650 DOI: 10.1016/j.tcb.2021.03.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Revised: 03/17/2021] [Accepted: 03/18/2021] [Indexed: 01/28/2023]
Abstract
Translocons are protein assemblies that facilitate the targeting and transport of proteins into and across biological membranes. Our understanding of these systems has been advanced using genetics, biochemistry, and structural biology. Despite these classic advances, until recently we have still largely lacked a detailed understanding of how translocons recognize and facilitate protein translocation. With the advent and improvements of cryogenic electron microscopy (cryo-EM) single-particle analysis and single-molecule fluorescence microscopy, the details of how translocons function are finally emerging. Here, we introduce these methods and evaluate their importance in understanding translocon structure, function, and dynamics.
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Affiliation(s)
- Madeline M Davis
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee at Knoxville, Knoxville, TN 37996, USA
| | - Rajan Lamichhane
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee at Knoxville, Knoxville, TN 37996, USA
| | - Barry D Bruce
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee at Knoxville, Knoxville, TN 37996, USA; Department of Microbiology, University of Tennessee at Knoxville, Knoxville, TN 37996, USA; Graduate Program in Genome Science and Technology, University of Tennessee at Knoxville, Knoxville, TN 37996, USA; Chemical and Biomolecular Engineering, University of Tennessee at Knoxville, Knoxville, TN 37996, USA.
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4
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A nexus of intrinsic dynamics underlies translocase priming. Structure 2021; 29:846-858.e7. [PMID: 33852897 DOI: 10.1016/j.str.2021.03.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Revised: 03/06/2021] [Accepted: 03/25/2021] [Indexed: 11/22/2022]
Abstract
The cytoplasmic ATPase SecA and the membrane-embedded SecYEG channel assemble to form the Sec translocase. How this interaction primes and catalytically activates the translocase remains unclear. We show that priming exploits a nexus of intrinsic dynamics in SecA. Using atomistic simulations, smFRET, and HDX-MS, we reveal multiple dynamic islands that cross-talk with domain and quaternary motions. These dynamic elements are functionally important and conserved. Central to the nexus is a slender stem through which rotation of the preprotein clamp of SecA is biased by ATPase domain motions between open and closed clamping states. An H-bonded framework covering most of SecA enables multi-tier dynamics and conformational alterations with minimal energy input. As a result, cognate ligands select preexisting conformations and alter local dynamics to regulate catalytic activity and clamp motions. These events prime the translocase for high-affinity reception of non-folded preprotein clients. Dynamics nexuses are likely universal and essential in multi-liganded proteins.
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Lira-Navarrete E, Pallarés MC, Castello F, Ruedas-Rama MJ, Orte A, Lostao A, Hurtado-Guerrero R. Protein O-Fucosyltransferase 1 Undergoes Interdomain Flexibility in Solution. Molecules 2021; 26:2105. [PMID: 33916911 PMCID: PMC8067585 DOI: 10.3390/molecules26082105] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2021] [Revised: 03/22/2021] [Accepted: 04/02/2021] [Indexed: 11/25/2022] Open
Abstract
Protein O-fucosyltransferase 1 (PoFUT1) is a GT-B fold enzyme that fucosylates proteins containing EGF-like repeats. GT-B glycosyltransferases have shown a remarkable grade of plasticity adopting closed and open conformations as a way of tuning their catalytic cycle, a feature that has not been observed for PoFUT1. Here, we analyzed Caenorhabditis elegans PoFUT1 (CePoFUT1) conformational behavior in solution by atomic force microscopy (AFM) and single-molecule fluorescence resonance energy transfer (SMF-FRET). Our results show that this enzyme is very flexible and adopts mainly compact conformations and to a lesser extend a highly dynamic population that oscillates between compact and highly extended conformations. Overall, our experiments illustrate the inherent complexity of CePoFUT1 dynamics, which might play a role during its catalytic cycle.
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Affiliation(s)
- Erandi Lira-Navarrete
- Institute of Biocomputation and Physics of Complex Systems (BIFI), University of Zaragoza, 50018 Zaragoza, Spain;
| | - María Carmen Pallarés
- Instituto de Nanociencia y Materiales de Aragón (INMA), CSIC-Universidad de Zaragoza, 50009 Zaragoza, Spain;
- Laboratorio de Microscopías Avanzadas (LMA), Universidad de Zaragoza, 50018 Zaragoza, Spain
| | - Fabio Castello
- Departamento de Fisicoquímica, Facultad de Farmacia, Universidad de Granada, 18071 Granada, Spain; (F.C.); (M.J.R.-R.)
| | - Maria J. Ruedas-Rama
- Departamento de Fisicoquímica, Facultad de Farmacia, Universidad de Granada, 18071 Granada, Spain; (F.C.); (M.J.R.-R.)
| | - Angel Orte
- Departamento de Fisicoquímica, Facultad de Farmacia, Universidad de Granada, 18071 Granada, Spain; (F.C.); (M.J.R.-R.)
| | - Anabel Lostao
- Instituto de Nanociencia y Materiales de Aragón (INMA), CSIC-Universidad de Zaragoza, 50009 Zaragoza, Spain;
- Laboratorio de Microscopías Avanzadas (LMA), Universidad de Zaragoza, 50018 Zaragoza, Spain
- Fundación ARAID, 50018 Zaragoza, Spain
| | - Ramón Hurtado-Guerrero
- Institute of Biocomputation and Physics of Complex Systems (BIFI), University of Zaragoza, 50018 Zaragoza, Spain;
- Laboratorio de Microscopías Avanzadas (LMA), Universidad de Zaragoza, 50018 Zaragoza, Spain
- Fundación ARAID, 50018 Zaragoza, Spain
- Copenhagen Center for Glycomics, Department of Cellular and Molecular Medicine, School of Dentistry, University of Copenhagen, 2200 Copenhagen, Denmark
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De Geyter J, Portaliou AG, Srinivasu B, Krishnamurthy S, Economou A, Karamanou S. Trigger factor is a bona fide secretory pathway chaperone that interacts with SecB and the translocase. EMBO Rep 2020; 21:e49054. [PMID: 32307852 DOI: 10.15252/embr.201949054] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Revised: 03/09/2020] [Accepted: 03/19/2020] [Indexed: 11/09/2022] Open
Abstract
Bacterial secretory preproteins are translocated across the inner membrane post-translationally by the SecYEG-SecA translocase. Mature domain features and signal peptides maintain preproteins in kinetically trapped, largely soluble, folding intermediates. Some aggregation-prone preproteins require chaperones, like trigger factor (TF) and SecB, for solubility and/or targeting. TF antagonizes the contribution of SecB to secretion by an unknown molecular mechanism. We reconstituted this interaction in vitro and studied targeting and secretion of the model preprotein pro-OmpA. TF and SecB display distinct, unsuspected roles in secretion. Tightly associating TF:pro-OmpA targets the translocase at SecA, but TF prevents pro-OmpA secretion. In solution, SecB binds TF:pro-OmpA with high affinity. At the membrane, when bound to the SecA C-tail, SecB increases TF and TF:pro-OmpA affinities for the translocase and allows pro-OmpA to resume translocation. Our data reveal that TF, a main cytoplasmic folding pathway chaperone, is also a bona fide post-translational secretory chaperone that directly interacts with both SecB and the translocase to mediate regulated protein secretion. Thus, TF links the cytoplasmic folding and secretion chaperone networks.
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Affiliation(s)
- Jozefien De Geyter
- Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, KU Leuven, Leuven, Belgium
| | - Athina G Portaliou
- Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, KU Leuven, Leuven, Belgium
| | - Bindu Srinivasu
- Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, KU Leuven, Leuven, Belgium
| | - Srinath Krishnamurthy
- Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, KU Leuven, Leuven, Belgium
| | - Anastassios Economou
- Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, KU Leuven, Leuven, Belgium
| | - Spyridoula Karamanou
- Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, KU Leuven, Leuven, Belgium
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Abstract
More than a third of all bacterial polypeptides, comprising the 'exportome', are transported to extracytoplasmic locations. Most of the exportome is targeted and inserts into ('membranome') or crosses ('secretome') the plasma membrane. The membranome and secretome use distinct targeting signals and factors, and driving forces, but both use the ubiquitous and essential Sec translocase and its SecYEG protein-conducting channel. Membranome export is co-translational and uses highly hydrophobic N-terminal signal anchor sequences recognized by the signal recognition particle on the ribosome, that also targets C-tail anchor sequences. Translating ribosomes drive movement of these polypeptides through the lateral gate of SecY into the inner membrane. On the other hand, secretome export is post-translational and carries two types of targeting signals: cleavable N-terminal signal peptides and multiple short hydrophobic targeting signals in their mature domains. Secretome proteins remain translocation competent due to occupying loosely folded to completely non-folded states during targeting. This is accomplished mainly by the intrinsic properties of mature domains and assisted by signal peptides and/or chaperones. Secretome proteins bind to the dimeric SecA subunit of the translocase. SecA converts from a dimeric preprotein receptor to a monomeric ATPase motor and drives vectorial crossing of chains through SecY aided by the proton motive force. Signal peptides are removed by signal peptidases and translocated chains fold or follow subsequent trafficking.
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Chattrakun K, Hoogerheide DP, Mao C, Randall LL, King GM. Protein Translocation Activity in Surface-Supported Lipid Bilayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:12246-12256. [PMID: 31448613 PMCID: PMC10906442 DOI: 10.1021/acs.langmuir.9b01928] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Surface-supported lipid bilayers are used widely throughout the nanoscience community as cellular membrane mimics. For example, they are frequently employed in single-molecule atomic force microscopy (AFM) studies to shed light on membrane protein conformational dynamics and folding. However, in AFM as well as in other surface-sensing techniques, the close proximity of the supporting surface raises questions about preservation of the biochemical activity. Employing the model translocase from the general secretory (Sec) system of Escherichia coli, here we quantify the activity via two biochemical assays in surface-supported bilayers. The first assesses ATP hydrolysis and the second assesses polypeptide translocation across the membrane via protection from added protease. Hydrolysis assays revealed distinct levels of activation ranging from medium (translocase-activated) to high (translocation-associated) that were similar to traditional solution experiments and further identified an adenosine triphosphatase population exhibiting characteristics of conformational hysteresis. Translocation assays revealed turn over numbers that were comparable to solution but with a 10-fold reduction in apparent rate constant. Despite differences in kinetics, the chemomechanical coupling (ATP hydrolyzed per residue translocated) only varied twofold on glass compared to solution. The activity changed with the topographic complexity of the underlying surface. Rough glass coverslips were favored over atomically flat mica, likely due to differences in frictional coupling between the translocating polypeptide and surface. Neutron reflectometry and AFM corroborated the biochemical measurements and provided structural characterization of the submembrane space and upper surface of the bilayer. Overall, the translocation activity was maintained for the surface-adsorbed Sec system, albeit with a slower rate-limiting step. More generally, polypeptide translocation activity measurements yield valuable quantitative metrics to assess the local environment about surface-supported lipid bilayers.
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Affiliation(s)
- Kanokporn Chattrakun
- Department of Physics and Astronomy, University of Missouri-Columbia, Columbia, Missouri 65211, United States
| | - David P. Hoogerheide
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Chunfeng Mao
- Department of Biochemistry, University of Missouri-Columbia, Columbia, Missouri 65211, United States
| | - Linda L. Randall
- Department of Biochemistry, University of Missouri-Columbia, Columbia, Missouri 65211, United States
| | - Gavin M. King
- Department of Physics and Astronomy, University of Missouri-Columbia, Columbia, Missouri 65211, United States
- Department of Biochemistry, University of Missouri-Columbia, Columbia, Missouri 65211, United States
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Catipovic MA, Bauer BW, Loparo JJ, Rapoport TA. Protein translocation by the SecA ATPase occurs by a power-stroke mechanism. EMBO J 2019; 38:embj.2018101140. [PMID: 30877095 DOI: 10.15252/embj.2018101140] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2018] [Revised: 01/25/2019] [Accepted: 01/31/2019] [Indexed: 11/09/2022] Open
Abstract
SecA belongs to the large class of ATPases that use the energy of ATP hydrolysis to perform mechanical work resulting in protein translocation across membranes, protein degradation, and unfolding. SecA translocates polypeptides through the SecY membrane channel during protein secretion in bacteria, but how it achieves directed peptide movement is unclear. Here, we use single-molecule FRET to derive a model that couples ATP hydrolysis-dependent conformational changes of SecA with protein translocation. Upon ATP binding, the two-helix finger of SecA moves toward the SecY channel, pushing a segment of the polypeptide into the channel. The finger retracts during ATP hydrolysis, while the clamp domain of SecA tightens around the polypeptide, preserving progress of translocation. The clamp opens after phosphate release and allows passive sliding of the polypeptide chain through the SecA-SecY complex until the next ATP binding event. This power-stroke mechanism may be used by other ATPases that move polypeptides.
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Affiliation(s)
- Marco A Catipovic
- Department of Cell Biology, Harvard Medical School, Boston, MA, USA.,Howard Hughes Medical Institute, Harvard Medical School, Boston, MA, USA
| | - Benedikt W Bauer
- Department of Cell Biology, Harvard Medical School, Boston, MA, USA.,Howard Hughes Medical Institute, Harvard Medical School, Boston, MA, USA
| | - Joseph J Loparo
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
| | - Tom A Rapoport
- Department of Cell Biology, Harvard Medical School, Boston, MA, USA .,Howard Hughes Medical Institute, Harvard Medical School, Boston, MA, USA
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