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Sannigrahi A, Chattopadhyay K. Pore formation by pore forming membrane proteins towards infections. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2021; 128:79-111. [PMID: 35034727 DOI: 10.1016/bs.apcsb.2021.09.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Over the last 25 years, the biology of membrane proteins, including the PFPs-membranes interactions is seeking attention for the development of successful drug molecules against a number of infectious diseases. Pore forming toxins (PFTs), the largest family of PFPs are considered as a group of virulence factors produced in a large number of pathogenic systems which include streptococcus, pneumonia, Staphylococcus aureus, E. coli, Mycobacterium tuberculosis, group A and B streptococci, Corynebacterium diphtheria and many more. PFTs are generally utilized by the disease causing pathogens to disrupt the host first line of defense i.e. host cell membranes through pore formation strategy. Although, pore formation is the principal mode of action of the PFTs but they can have additional adverse effects on the hosts including immune evasion. Recently, structural investigation of different PFTs have imparted the molecular mechanistic insights into how PFTs get transformed from its inactive state to active toxic state. On the basis of their structural entity, PFTs have been classified in different types and their mode of actions alters in terms of pore formation and corresponding cellular toxicity. Although pathogen genome analysis can identify the probable PFTs depending upon their structural diversity, there are so many PFTs which utilize the local environmental conditions to generate their pore forming ability using a novel strategy which is known as "conformational switch" of a protein. This conformational switch is considered as characteristics of the phase shifting proteins which were often utilized by many pathogenic systems to protect them from the invaders through allosteric communication between distant regions of the protein. In this chapter, we discuss the structure function relationships of PFTs and how activity of PFTs varies with the change in the environmental conditions has been explored. Finally, we demonstrate these structural insights to develop therapeutic potential to treat the infections caused by multidrug resistant pathogens.
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Affiliation(s)
- Achinta Sannigrahi
- Department of Chemical Engineering, Indian Institute of Science, Bengaluru, Karnataka, India.
| | - Krishnananda Chattopadhyay
- Structural Biology and Bioinformatics Division, CSIR-Indian Institute of Chemical Biology, Kolkata, West Bengal, India.
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Glycolipozyme MPIase is essential for topology inversion of SecG during preprotein translocation. Proc Natl Acad Sci U S A 2013; 110:9734-9. [PMID: 23716687 DOI: 10.1073/pnas.1303160110] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Presecretory proteins are translocated across biological membranes through protein-conducting channels such as Sec61 (eukaryotes) and SecYEG (bacteria). SecA, a translocation ATPase, pushes preproteins out with dynamic structural changes through SecYEG. SecG, a subunit of the SecYEG channel possessing two transmembrane stretches (TMs), undergoes topology inversion coupled with SecA-dependent translocation. Recently, we characterized membrane protein integrase (MPIase), a glycolipozyme involved in not only protein integration into membranes but also preprotein translocation. We report here that SecG inversion occurs only when MPIase associates with SecYEG. We also found that MPIase modulates the dimer orientation of SecYEG. Cysteine-scanning mutagenesis mapped SecG TM 2 to a relatively hydrophilic environment. The dimer formation of SecG, crosslinked at TM 2, was not observed on SecG inversion, indicating that SecYEG undergoes a dynamic structural change during preprotein translocation.
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Solov'eva TF, Novikova OD, Portnyagina OY. Biogenesis of β-barrel integral proteins of bacterial outer membrane. BIOCHEMISTRY (MOSCOW) 2013; 77:1221-36. [PMID: 23240560 DOI: 10.1134/s0006297912110016] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Gram-negative bacteria are enveloped by two membranes, the inner (cytoplasmic) (CM) and the outer (OM). The majority of integral outer membrane proteins are arranged in β-barrels of cylindrical shape composed of amphipathic antiparallel β-strands. In bacteria, β-barrel proteins function as water-filled pores, active transporters, enzymes, receptors, and structural proteins. Proteins of bacterial OM are synthesized in the cytoplasm as unfolded polypeptides with an N-terminal sequence that marks them for transport across the CM. Precursors of membrane proteins move through the aqueous medium of the cytosol and periplasm under the protection of chaperones (SecB, Skp, SurA, and DegP), then cross the CM via the Sec system composed of a polypeptide-conducting channel (SecYEG) and ATPase (SecA), the latter providing the energy for the translocation of the pre-protein. Pre-protein folding and incorporation in the OM require the participation of the Bam-complex, probably without the use of energy. This review summarizes current data on the biogenesis of the β-barrel proteins of bacterial OM. Data on the structure of the proteins included in the multicomponent system for delivery of the OM proteins to their destination in the cell and on their complexes with partners, including pre-proteins, are presented. Molecular models constructed on the basis of structural, genetic, and biochemical studies that describe the mechanisms of β-barrel protein assembly by this molecular transport machinery are also considered.
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Affiliation(s)
- T F Solov'eva
- Elyakov Pacific Institute of Bioorganic Chemistry, Russian Academy of Sciences, Vladivostok, 690022, Russia.
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Dalbey RE, Kuhn A. Protein Traffic in Gram-negative bacteria – how exported and secreted proteins find their way. FEMS Microbiol Rev 2012; 36:1023-45. [DOI: 10.1111/j.1574-6976.2012.00327.x] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2011] [Accepted: 01/04/2012] [Indexed: 11/27/2022] Open
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A single copy of SecYEG is sufficient for preprotein translocation. EMBO J 2011; 30:4387-97. [PMID: 21897368 DOI: 10.1038/emboj.2011.314] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Accepted: 07/15/2011] [Indexed: 11/08/2022] Open
Abstract
The heterotrimeric SecYEG complex comprises a protein-conducting channel in the bacterial cytoplasmic membrane. SecYEG functions together with the motor protein SecA in preprotein translocation. Here, we have addressed the functional oligomeric state of SecYEG when actively engaged in preprotein translocation. We reconstituted functional SecYEG complexes labelled with fluorescent markers into giant unilamellar vesicles at a natively low density. Förster's resonance energy transfer and fluorescence (cross-) correlation spectroscopy with single-molecule sensitivity allowed for independent observations of the SecYEG and preprotein dynamics, as well as complex formation. In the presence of ATP and SecA up to 80% of the SecYEG complexes were loaded with a preprotein translocation intermediate. Neither the interaction with SecA nor preprotein translocation resulted in the formation of SecYEG oligomers, whereas such oligomers can be detected when enforced by crosslinking. These data imply that the SecYEG monomer is sufficient to form a functional translocon in the lipid membrane.
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Martínez-Gil L, Saurí A, Marti-Renom MA, Mingarro I. Membrane protein integration into the endoplasmic reticulum. FEBS J 2011; 278:3846-58. [PMID: 21592307 DOI: 10.1111/j.1742-4658.2011.08185.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Most integral membrane proteins are targeted, inserted and assembled in the endoplasmic reticulum membrane. The sequential and potentially overlapping events necessary for membrane protein integration take place at sites termed translocons, which comprise a specific set of membrane proteins acting in concert with ribosomes and, probably, molecular chaperones to ensure the success of the whole process. In this minireview, we summarize our current understanding of helical membrane protein integration at the endoplasmic reticulum, and highlight specific characteristics that affect the biogenesis of multispanning membrane proteins.
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Affiliation(s)
- Luis Martínez-Gil
- Departament de Bioquímica i Biologia Molecular, Universitat de València, Burjassot, Spain
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Tang Y, Pan X, Tai PC, Sui S. Electron microscopic visualization of asymmetric precursor translocation intermediates: SecA functions as a dimer. SCIENCE CHINA-LIFE SCIENCES 2010; 53:1049-56. [PMID: 21104364 DOI: 10.1007/s11427-010-4061-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2010] [Accepted: 07/22/2010] [Indexed: 11/27/2022]
Abstract
SecA, the ATPase of Sec translocase, mediates the post-translational translocation of preprotein through the protein-conducting channel SecYEG in the bacterial inner membrane. Here we report the structures of Escherichia coli Sec intermediates during preprotein translocation as visualized by electron microscopy to probe the oligomeric states of SecA during this process. We found that the translocase holoenzyme is symmetrically assembled by SecA and SecYEG on proteoliposomes, whereas the translocation intermediate 31 (I(31)) becomes asymmetric because of the presence of preprotein. Moreover, SecA is a dimer in these two translocation complexes. This work also shows surface topological changes in the components of translocation intermediates by immunogold labeling. The channel entry for preprotein translocation was found at the center of the I(31) structures. Our results indicate that the presence of preprotein introduces asymmetry into translocation intermediates, while SecA remains dimeric during the translocation process.
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Affiliation(s)
- Ying Tang
- State-Key Laboratory of Biomembrane and Membrane Biotechnology, Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China
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Facey SJ, Kuhn A. Biogenesis of bacterial inner-membrane proteins. Cell Mol Life Sci 2010; 67:2343-62. [PMID: 20204450 PMCID: PMC11115511 DOI: 10.1007/s00018-010-0303-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2009] [Revised: 02/01/2010] [Accepted: 02/03/2010] [Indexed: 11/26/2022]
Abstract
All cells must traffic proteins into and across their membranes. In bacteria, several pathways have evolved to enable protein transfer across the inner membrane, the periplasm, and the outer membrane. The major route of protein translocation in and across the cytoplasmic membrane is the general secretion pathway (Sec-pathway). The biogenesis of membrane proteins not only requires protein translocation but also coordinated targeting to the membrane beforehand and folding and assembly into their protein complexes afterwards to function properly in the cell. All these processes are responsible for the biogenesis of membrane proteins that mediate essential functions of the cell such as selective transport, energy conversion, cell division, extracellular signal sensing, and motility. This review will highlight the most recent developments on the structure and function of bacterial membrane proteins, focusing on the journey that integral membrane proteins take to find their final destination in the inner membrane.
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Affiliation(s)
- Sandra J. Facey
- Institute of Microbiology, University of Hohenheim, 70599 Stuttgart, Germany
| | - Andreas Kuhn
- Institute of Microbiology, University of Hohenheim, 70599 Stuttgart, Germany
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Becker T, Bhushan S, Jarasch A, Armache JP, Funes S, Jossinet F, Gumbart J, Mielke T, Berninghausen O, Schulten K, Westhof E, Gilmore R, Mandon EC, Beckmann R. Structure of monomeric yeast and mammalian Sec61 complexes interacting with the translating ribosome. Science 2009; 326:1369-73. [PMID: 19933108 DOI: 10.1126/science.1178535] [Citation(s) in RCA: 222] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The trimeric Sec61/SecY complex is a protein-conducting channel (PCC) for secretory and membrane proteins. Although Sec complexes can form oligomers, it has been suggested that a single copy may serve as an active PCC. We determined subnanometer-resolution cryo-electron microscopy structures of eukaryotic ribosome-Sec61 complexes. In combination with biochemical data, we found that in both idle and active states, the Sec complex is not oligomeric and interacts mainly via two cytoplasmic loops with the universal ribosomal adaptor site. In the active state, the ribosomal tunnel and a central pore of the monomeric PCC were occupied by the nascent chain, contacting loop 6 of the Sec complex. This provides a structural basis for the activity of a solitary Sec complex in cotranslational protein translocation.
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Affiliation(s)
- Thomas Becker
- Gene Center Munich and Center for Integrated Protein Science, Department of Chemistry and Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
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Boy D, Koch HG. Visualization of distinct entities of the SecYEG translocon during translocation and integration of bacterial proteins. Mol Biol Cell 2009; 20:1804-15. [PMID: 19158385 DOI: 10.1091/mbc.e08-08-0886] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The universally conserved SecYEG/Sec61 translocon constitutes the major protein-conducting channel in the cytoplasmic membrane of bacteria and the endoplasmic reticulum membrane of eukaryotes. It is engaged in both translocating secretory proteins across the membrane as well as in integrating membrane proteins into the lipid phase of the membrane. In the current study we have detected distinct SecYEG translocon complexes in native Escherichia coli membranes. Blue-Native-PAGE revealed the presence of a 200-kDa SecYEG complex in resting membranes. When the SecA-dependent secretory protein pOmpA was trapped inside the SecYEG channel, a smaller SecY-containing complex of approximately 140-kDa was observed, which probably corresponds to a monomeric SecYEG-substrate complex. Trapping the SRP-dependent polytopic membrane protein mannitol permease in the SecYEG translocon, resulted in two complexes of 250 and 600 kDa, each containing both SecY and the translocon-associated membrane protein YidC. The appearance of both complexes was correlated with the number of transmembrane domains that were exposed during targeting of mannitol permease to the membrane. These results suggest that the assembly or the stability of the bacterial SecYEG translocon is influenced by the substrate that needs to be transported.
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Affiliation(s)
- Diana Boy
- Institut für Biochemie und Molekularbiologie, ZBMZ, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany
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A single Sec61-complex functions as a protein-conducting channel. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1783:2375-83. [DOI: 10.1016/j.bbamcr.2008.08.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2008] [Revised: 08/06/2008] [Accepted: 08/06/2008] [Indexed: 12/30/2022]
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Karamanou S, Bariami V, Papanikou E, Kalodimos CG, Economou A. Assembly of the translocase motor onto the preprotein-conducting channel. Mol Microbiol 2008; 70:311-22. [PMID: 18761620 DOI: 10.1111/j.1365-2958.2008.06402.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Bacterial protein secretion is catalysed by the SecYEG protein-conducting channel complexed with the SecA ATPase motor. To gain insight into the SecA-SecYEG interaction we used peptide arrays, thermodynamic quantification, mutagenesis and functional assays. Our data reveal that: (i) SecA binds with low affinity on several, peripheral, exposed SecYEG sites. This largely electrostatic association is modulated by temperature and nucleotides. (ii) Binding sites cluster in five major binding 'regions': three that are exclusively cytoplasmic and two that reach the periplasm. (iii) Both the N-terminal and c-terminal regions of SecA participate in binding interactions and share some sites. (iv) Several of these sites are essential for translocase catalysis. Our data provide residue-level dissection of the SecYEG-SecA interaction. Two models of assembly of SecA on dimeric SecYEG are discussed.
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Affiliation(s)
- Spyridoula Karamanou
- Institute of Molecular Biology and Biotechnology-FoRTH, PO Box 1385, Iraklio, Crete, Greece
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Antonoaea R, Fürst M, Nishiyama KI, Müller M. The periplasmic chaperone PpiD interacts with secretory proteins exiting from the SecYEG translocon. Biochemistry 2008; 47:5649-56. [PMID: 18439025 DOI: 10.1021/bi800233w] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The Sec translocon of Escherichia coli mediates the export of numerous secretory and membrane proteins. To dissect the passage of an exported protein across the Sec translocon into consecutive steps, we generated in vitro translocation intermediates of a polypeptide chain, which by its N-terminus is anchored in the membrane and by its C-terminus tethered to the ribosome. We find that in this situation, the motor protein SecA propagates translocation of a peptide loop across SecYEG prior to the removal of ribosomes. Upon SecA-driven exit from the translocon, this loop is brought into the immediate vicinity of the membrane-anchored, periplasmic chaperone PpiD. Consistent with a coupling between translocation across the SecYEG translocon and folding by periplasmic chaperones, a lack of PpiD retards the release of a translocating outer membrane protein into the periplasm.
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Affiliation(s)
- Raluca Antonoaea
- Institut für Biochemie and Molekularbiologie and Zentrum für Biochemie and Molekulare Zellforschung, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany
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Rusch SL, Kendall DA. Oligomeric states of the SecA and SecYEG core components of the bacterial Sec translocon. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2006; 1768:5-12. [PMID: 17011510 PMCID: PMC2712355 DOI: 10.1016/j.bbamem.2006.08.013] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2006] [Revised: 07/27/2006] [Accepted: 08/18/2006] [Indexed: 10/24/2022]
Abstract
Many proteins synthesized in the cytoplasm ultimately function in non-cytoplasmic locations. In Escherichia coli, the general secretory (Sec) pathway transports the vast majority of these proteins. Two fundamental components of the Sec transport pathway are the SecYEG heterotrimeric complex that forms the channel through the cytoplasmic membrane, and SecA, the ATPase that drives the preprotein to and across the membrane. This review focuses on what is known about the oligomeric states of these core Sec components and how the oligomeric state might change during the course of the translocation of a preprotein.
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Affiliation(s)
| | - Debra A. Kendall
- Corresponding author. Tel.: +1 860 486 1891. E-mail address: (D.A. Kendall)
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Abstract
The translocon is a protein-conducting channel conserved over all domains of life that serves to translocate proteins across or into membranes. Although this channel has been well studied for many years, the recent discovery of a high-resolution crystal structure opens up new avenues of exploration. Taking advantage of this, we performed molecular dynamics simulations of the translocon in a fully solvated lipid bilayer, examining the translocation abilities of monomeric SecYEbeta by forcing two helices comprised of different amino acid sequences to cross the channel. The simulations revealed that the so-called plug of SecYEbeta swings open during translocation, closing thereafter. Likewise, it was established that the so-called pore ring region of SecYEbeta forms an elastic, yet tight, seal around the translocating oligopeptides. The closed state of the channel was found to block permeation of all ions and water molecules; in the open state, ions were blocked. Our results suggest that the SecYEbeta monomer is capable of forming an active channel.
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Affiliation(s)
- James Gumbart
- Department of Physics, University of Illinois at Urbana-Champaign and Beckman Institute for Advanced Science and Technology, Urbana, Illinois 61801, USA
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Abstract
Gram-negative bacteria such as Escherichia coli are surrounded by two membranes, the inner membrane and the outer membrane. The biogenesis of most inner membrane proteins (IMPs), typical alpha-helical proteins, appears to follow a partly conserved cotranslational pathway. Targeting involves a relatively simple signal recognition particle (SRP) and SRP-receptor. Insertion of most IMPs into the membrane occurs via the Sec-translocon, which is also used for the vectorial transport of secretory proteins. Similar to eukaryotic systems, little is known about the later stages of biogenesis of IMPs, the folding and assembly in the lipid bilayer. Recently, YidC has been identified as a factor that assists in the integration, folding, and assembly of IMPs both in association with the Sec-translocon and separately. This review deals mainly with recent structural and biochemical data from various experimental systems that offer new insight into the different stages of biogenesis of E. coli IMPs.
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Affiliation(s)
- Joen Luirink
- Department of Microbiology, Institute of Molecular Cell Biology, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands.
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Abstract
Subcellular compartments have unique protein compositions, yet protein synthesis only occurs in the cytosol and in mitochondria and chloroplasts. How do proteins get where they need to go? The first steps are targeting to an organelle and efficient translocation across its limiting membrane. Given that most transport systems are exquisitely substrate specific, how are diverse protein sequences recognized for translocation? Are they translocated as linear polypeptide chains or after folding? During translocation, how are diverse amino acyl side chains accommodated? What are the proteins and the lipid environment that catalyze transport and couple it to energy? How is translocation coordinated with protein synthesis and folding, and how are partially translocated transmembrane proteins released into the lipid bilayer? We review here the marked progress of the past 35 years and salient questions for future work. Subcellular compartments have unique protein compositions, yet protein synthesis only occurs in the cytosol and in mitochondria and chloroplasts. How do proteins get where they need to go? The first steps are targeting to an organelle and efficient translocation across its limiting membrane. Given that most transport systems are exquisitely substrate specific, how are diverse protein sequences recognized for translocation? Are they translocated as linear polypeptide chains or after folding? During translocation, how are diverse amino acyl side chains accommodated? What are the proteins and the lipid environment that catalyze transport and couple it to energy? How is translocation coordinated with protein synthesis and folding, and how are partially translocated transmembrane proteins released into the lipid bilayer? We review here the marked progress of the past 35 years and salient questions for future work.
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Affiliation(s)
- William Wickner
- Department of Biological Chemistry, Dartmouth Medical School, 7200 Vail Building, Hanover, NH 03755-3844, USA.
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Scheuring J, Braun N, Nothdurft L, Stumpf M, Veenendaal AKJ, Kol S, van der Does C, Driessen AJM, Weinkauf S. The oligomeric distribution of SecYEG is altered by SecA and translocation ligands. J Mol Biol 2005; 354:258-71. [PMID: 16242710 DOI: 10.1016/j.jmb.2005.09.058] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2005] [Revised: 08/30/2005] [Accepted: 09/20/2005] [Indexed: 11/23/2022]
Abstract
The multimeric membrane protein complex translocase mediates the transport of preproteins across and integration of membrane proteins into the inner membrane of Escherichia coli. The translocase consists of the peripheral membrane-associated ATPase SecA and the heterotrimeric channel-forming complex consisting of SecY, SecE and SecG. We have investigated the quaternary structure of the SecYEG complex in proteoliposomes. Fluorescence resonance energy transfer demonstrates that SecYEG forms oligomers when embedded in the membrane. Freeze-fracture techniques were used to examine the oligomeric composition under non-translocating and translocating conditions. Our data show that membrane-embedded SecYEG exists in a concentration-dependent equilibrium between monomers, dimers and tetramers, and that dynamic exchange of subunits between oligomers can occur. Remarkably, the formation of dimers and tetramers in the lipid environment is stimulated significantly by membrane insertion of SecA and by the interaction with translocation ligands SecA, preprotein and ATP, suggesting that the active translocation channel consists of multiple SecYEG complexes.
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Affiliation(s)
- Johannes Scheuring
- Department of Chemistry, Technical University Munich, Lichtenbergstr. 4, 85747 Garching, Germany
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Deitermann S, Sprie GS, Koch HG. A dual function for SecA in the assembly of single spanning membrane proteins in Escherichia coli. J Biol Chem 2005; 280:39077-85. [PMID: 16186099 DOI: 10.1074/jbc.m509647200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The assembly of bacterial membrane proteins with large periplasmic loops is an intrinsically complex process because the SecY translocon has to coordinate the signal recognition particle-dependent targeting and integration of transmembrane domains with the SecA-dependent translocation of the periplasmic loop. The current model suggests that the ATP hydrolysis by SecA is required only if periplasmic loops larger than 30 amino acids have to be translocated. In agreement with this model, our data demonstrate that the signal recognition particle- and SecA-dependent multiple spanning membrane protein YidC becomes SecA-independent if the large periplasmic loop connecting transmembrane domains 1 and 2 is reduced to less than 30 amino acids. Strikingly, however, we were unable to render single spanning membrane proteins SecA-independent by reducing the length of their periplasmic loops. For these proteins, the complete assembly was always SecA-dependent even if the periplasmic loop was reduced to 13 amino acids. If, however, the 13-amino acid-long periplasmic loop was fused to a downstream transmembrane domain, SecA was no longer required for complete translocation. Although these data support the current model on the SecA dependence of multiple spanning membrane proteins, they indicate a novel function of SecA for the assembly of single spanning membrane proteins. This could suggest that single and multiple spanning membrane proteins are processed differently by the bacterial SecY translocon.
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Affiliation(s)
- Sandra Deitermann
- Institute for Biochemistry and Molecular Biology, Faculty for Medicine, University Freiburg, 79104 Freiburg, Federal Republic of Germany
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Tam PCK, Maillard AP, Chan KKY, Duong F. Investigating the SecY plug movement at the SecYEG translocation channel. EMBO J 2005; 24:3380-8. [PMID: 16148946 PMCID: PMC1276166 DOI: 10.1038/sj.emboj.7600804] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2005] [Accepted: 08/11/2005] [Indexed: 11/09/2022] Open
Abstract
Protein translocation occurs across the energy-conserving bacterial membrane at the SecYEG channel. The crystal structure of the channel has revealed a possible mechanism for gating and opening. This study evaluates the plug hypothesis using cysteine crosslink experiments in combination with various allelic forms of the Sec complex. The results demonstrate that the SecY plug domain moves away from the center of the channel toward SecE during polypeptide translocation, and further show that the translocation-enhancing prlA3 mutation and SecG subunit change the properties of channel gating. Locking the plug in the open state preactivates the Sec complex, and a super-active translocase can be created when combined with the prlA4 mutation located in the pore of the channel. Dimerization of the Sec complex, which is essential for translocase activity, relocates the plug toward the open position. We propose that oligomerization may result in SecYEG cooperative interactions important to prime the translocon function.
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Affiliation(s)
- Patrick C K Tam
- Department of Biochemistry & Molecular Biology, Faculty of Medicine, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada
| | - Antoine P Maillard
- Department of Biochemistry & Molecular Biology, Faculty of Medicine, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada
| | - Kenneth K Y Chan
- Department of Biochemistry & Molecular Biology, Faculty of Medicine, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada
| | - Franck Duong
- Department of Biochemistry & Molecular Biology, Faculty of Medicine, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada
- Department of Biochemistry & Molecular Biology, Faculty of Medicine, Life Sciences Institute, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, Canada V6T 1Z3. Tel.: +1 604 822 5975; Fax: +1 604 822 5227; E-mail:
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Jilaveanu LB, Zito CR, Oliver D. Dimeric SecA is essential for protein translocation. Proc Natl Acad Sci U S A 2005; 102:7511-6. [PMID: 15897468 PMCID: PMC1140455 DOI: 10.1073/pnas.0502774102] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
SecA facilitates bacterial protein translocation by its association with presecretory or membrane proteins and the SecYEG translocon channel. Once assembled, SecA ATPase undergoes cycles of membrane insertion and retraction at SecYEG that drive protein translocation in a stepwise fashion. SecA exists in equilibrium between a monomer and dimer, and association with its translocation ligands shifts this equilibrium dramatically. Here, we examined the proposal that protein translocation can occur by means of a SecA monomer. We produced a mutant SecA protein lacking residues 2-11, which was found to exist mostly as a monomer, and it was unable to complement a conditional-lethal secA mutant, was inactive for in vitro protein translocation, and was poorly active for translocation ATPase activity. Furthermore, we developed a technique termed membrane trapping, where wild-type SecA subunits became trapped within the membrane by overproduction of membrane-stuck mutant SecA proteins, and, in one case, a membrane-associated SecA heterodimer was demonstrated. Finally, we examined both endogenous and reconstituted membrane-bound SecA and found a significant level of SecA dimer in both cases, as assessed by chemical crosslinking. Collectively, our results strongly suggest that membrane-bound SecA dimer is critical for the protein translocation cycle, although these results cannot exclude participation of SecA monomer at some stage in the translocation process. Our findings have important implications regarding SecA motor function and translocon assembly and activation.
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Affiliation(s)
- Lucia B Jilaveanu
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, CT 06459, USA
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22
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Mergulhão FJM, Summers DK, Monteiro GA. Recombinant protein secretion in Escherichia coli. Biotechnol Adv 2005; 23:177-202. [PMID: 15763404 DOI: 10.1016/j.biotechadv.2004.11.003] [Citation(s) in RCA: 334] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2004] [Revised: 11/23/2004] [Accepted: 11/30/2004] [Indexed: 10/25/2022]
Abstract
The secretory production of recombinant proteins by the Gram-negative bacterium Escherichia coli has several advantages over intracellular production as inclusion bodies. In most cases, targeting protein to the periplasmic space or to the culture medium facilitates downstream processing, folding, and in vivo stability, enabling the production of soluble and biologically active proteins at a reduced process cost. This review presents several strategies that can be used for recombinant protein secretion in E. coli and discusses their advantages and limitations depending on the characteristics of the target protein to be produced.
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Affiliation(s)
- F J M Mergulhão
- Centro de Engenharia Biológica e Química, Instituto Superior Técnico, Av. Rovisco Pais, Lisbon 1049-001, Portugal.
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23
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Wang L, Miller A, Rusch SL, Kendall DA. Demonstration of a specific Escherichia coli SecY-signal peptide interaction. Biochemistry 2004; 43:13185-92. [PMID: 15476412 PMCID: PMC3084660 DOI: 10.1021/bi049485k] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Protein translocation in Escherichia coli is initiated by the interaction of a preprotein with the membrane translocase composed of a motor protein, SecA ATPase, and a membrane-embedded channel, the SecYEG complex. The extent to which the signal peptide region of the preprotein plays a role in SecYEG interactions is unclear, in part because studies in this area typically employ the entire preprotein. Using a synthetic signal peptide harboring a photoaffinity label in its hydrophobic core, we examined this interaction with SecYEG in a detergent micellar environment. The signal peptide was found to specifically bind SecY in a saturable manner and at levels comparable to those that stimulate SecA ATPase activity. Chemical and proteolytic cleavage of cross-linked SecY and analysis of the signal peptide adducts indicate that the binding was primarily to regions of the protein containing transmembrane domains seven and two. The signal peptide-SecY interaction was affected by the presence of SecA and nucleotides in a manner consistent with the transfer of signal peptide to SecY upon nucleotide hydrolysis at SecA.
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Affiliation(s)
| | | | | | - Debra A. Kendall
- To whom correspondence should be addressed: Department of Molecular and Cell Biology, 91 North Eagleville Road, The University of Connecticut, Storrs, CT 06269-3125. Tel: (860) 486-1891.
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24
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Veenendaal AKJ, van der Does C, Driessen AJM. The protein-conducting channel SecYEG. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2004; 1694:81-95. [PMID: 15546659 DOI: 10.1016/j.bbamcr.2004.02.009] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2003] [Revised: 01/30/2004] [Accepted: 02/02/2004] [Indexed: 10/26/2022]
Abstract
In bacteria, the translocase mediates the translocation of proteins into or across the cytosolic membrane. It consists of a membrane embedded protein-conducting channel and a peripherally associated motor domain, the ATPase SecA. The channel is formed by SecYEG, a multimeric protein complex that assembles into oligomeric forms. The structure and subunit composition of this protein-conducting channel is evolutionary conserved and a similar system is found in the endoplasmic reticulum of eukaryotes and the cytoplasmic membrane of archaea. The ribosome and other membrane proteins can associate with the protein-conducting channel complex and affect its activity or functionality.
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Affiliation(s)
- Andreas K J Veenendaal
- Department of Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9750 AA Haren, The Netherlands
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25
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Dalbey RE, Chen M. Sec-translocase mediated membrane protein biogenesis. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2004; 1694:37-53. [DOI: 10.1016/j.bbamcr.2004.03.009] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2003] [Revised: 03/08/2004] [Accepted: 03/09/2004] [Indexed: 10/26/2022]
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26
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Tziatzios C, Schubert D, Lotz M, Gundogan D, Betz H, Schägger H, Haase W, Duong F, Collinson I. The bacterial protein-translocation complex: SecYEG dimers associate with one or two SecA molecules. J Mol Biol 2004; 340:513-24. [PMID: 15210351 DOI: 10.1016/j.jmb.2004.04.076] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2004] [Revised: 04/26/2004] [Accepted: 04/30/2004] [Indexed: 11/25/2022]
Abstract
In bacteria, the Sec-protein transport complex facilitates the passage of most secretory and membrane proteins across and into the plasma membrane. The core complex SecYEG forms the protein channel and engages either ribosomes or the ATPase SecA, which drive translocation of unfolded polypeptide chains through the complex and into the periplasmic space. Escherichia coli SecYEG forms dimers in membranes, but in detergent solution the population of these dimers is low. However, we find that stable dimers can be assembled by the addition of a monoclonal antibody. Normally, a stable SecYEG-SecA complex can only form on isolated membranes or on reconstituted proteo-liposomes. The antibody-stabilised SecYEG dimer binds one SecA molecule in detergent solution. In the presence of AMPPNP, a non-hydrolysable analogue of ATP, a complex forms containing one antibody and two each of SecYEG and SecA. SecYEG monomers or tetramers do not associate to a significant degree with SecA. The observed variability in the stoichiometry of SecYEG and SecA association and its nucleotide modulation may be important and necessary for the protein translocation reaction.
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Affiliation(s)
- Christos Tziatzios
- Institute für Biophysik, JWG-Universität, 60590 Frankfurt am Main, Germany
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27
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de Gier JWL, Luirink J. The ribosome and YidC. New insights into the biogenesis of Escherichia coli inner membrane proteins. EMBO Rep 2004; 4:939-43. [PMID: 14528263 PMCID: PMC1326391 DOI: 10.1038/sj.embor.embor921] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2003] [Accepted: 07/21/2003] [Indexed: 11/08/2022] Open
Abstract
In the bacterium Escherichia coli, inner membrane proteins (IMPs) are generally targeted through the signal recognition particle pathway to the Sec translocon, which is capable of both linear transport into the periplasm and lateral transport into the lipid bilayer. Lateral transport seems to be assisted by the IMP YidC. In this article, we discuss recent observations that point to a key role for the ribosome in IMP targeting and to the diverse roles of YidC in IMP assembly.
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Affiliation(s)
- Jan-Willem L de Gier
- Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, SE-106 91 Stockholm, Sweden.
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28
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Belin D, Guzman LM, Bost S, Konakova M, Silva F, Beckwith J. Functional activity of eukaryotic signal sequences in Escherichia coli: the ovalbumin family of serine protease inhibitors. J Mol Biol 2004; 335:437-53. [PMID: 14672654 DOI: 10.1016/j.jmb.2003.10.076] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
It is widely assumed that the functional activity of signal sequences has been conserved throughout evolution, at least between Gram-negative bacteria and eukaryotes. The ovalbumin family of serine protease inhibitors (serpins) provides a unique tool to test this assumption, since individual members can be secreted (ovalbumin), cytosolic (leukocyte elastase inhibitor, LEI), or targeted to both compartments (plasminogen activator inhibitor 2, PAI-2). The facultative secretion of PAI-2 is mediated by a signal sequence proposed to be inefficient by design. We show here that the same internal domain that promotes an inefficient translocation of murine PAI-2 in mammalian cells is a weak signal sequence in Escherichia coli. In contrast, the ovalbumin signal sequence is much more efficient, whereas the corresponding sequence elements from LEI, maspin and PI-10 are entirely devoid of signal sequence activity in E.coli. Mutations that improve the activity of the PAI-2 signal sequence and that convert the N-terminal regions of maspin and PI-10 into efficient signal sequences have been characterized. Taken together, these results indicate that several structural features contribute to the weak activity of the PAI-2 signal sequence and provide new insights into the plasticity of the "hydrophobic core" of signal sequences. High-level expression of two chimeric proteins containing the PAI-2 signal sequence is toxic, and the reduced viability is accompanied by a rapid decrease in the membrane proton motive force, in ATP levels and in translation. In unc- cells, which lack the F0F1 ATP-synthase, the chimeric proteins retain their toxicity and their expression only affected the proton motive force. Thus, the properties of these toxic signal sequences offer a new tool to dissect the interactions of signal sequences with the protein export machinery.
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Affiliation(s)
- D Belin
- Département de Pathologie, Université de Genève, CH-1211 Geneva, Switzerland.
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29
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Pohlschröder M, Dilks K, Hand NJ, Wesley Rose R. Translocation of proteins across archaeal cytoplasmic membranes. FEMS Microbiol Rev 2004; 28:3-24. [PMID: 14975527 DOI: 10.1016/j.femsre.2003.07.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2003] [Revised: 07/03/2003] [Accepted: 07/09/2003] [Indexed: 11/20/2022] Open
Abstract
All cells need to transport proteins across hydrophobic membranes. Several mechanisms have evolved to facilitate this transport, including: (i) the universally-conserved Sec system, which transports proteins in an unfolded conformation and is thought to be the major translocation pathway in most organisms and (ii) the Tat system, which transports proteins that have already obtained some degree of tertiary structure. Here, we present the current understanding of these processes in the domain Archaea, and how they compare to the corresponding pathways in bacteria and eukaryotes.
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Affiliation(s)
- Mechthild Pohlschröder
- Department of Biology, University of Pennsylvania, 415 University Avenue, 201 Leidy Labs, Philadelphia, PA 19104-6018, USA.
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30
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Affiliation(s)
- Bernhard Dobberstein
- Zentrum für Molekulare Biologie and I. Sinning is at the Biochemiezentrum, Universität Heidelberg, 69120 Heidelberg, Germany.
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31
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32
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Van den Berg B, Clemons WM, Collinson I, Modis Y, Hartmann E, Harrison SC, Rapoport TA. X-ray structure of a protein-conducting channel. Nature 2003; 427:36-44. [PMID: 14661030 DOI: 10.1038/nature02218] [Citation(s) in RCA: 932] [Impact Index Per Article: 44.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2003] [Accepted: 11/19/2003] [Indexed: 11/09/2022]
Abstract
A conserved heterotrimeric membrane protein complex, the Sec61 or SecY complex, forms a protein-conducting channel, allowing polypeptides to be transferred across or integrated into membranes. We report the crystal structure of the complex from Methanococcus jannaschii at a resolution of 3.2 A. The structure suggests that one copy of the heterotrimer serves as a functional translocation channel. The alpha-subunit has two linked halves, transmembrane segments 1-5 and 6-10, clamped together by the gamma-subunit. A cytoplasmic funnel leading into the channel is plugged by a short helix. Plug displacement can open the channel into an 'hourglass' with a ring of hydrophobic residues at its constriction. This ring may form a seal around the translocating polypeptide, hindering the permeation of other molecules. The structure also suggests mechanisms for signal-sequence recognition and for the lateral exit of transmembrane segments of nascent membrane proteins into lipid, and indicates binding sites for partners that provide the driving force for translocation.
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Affiliation(s)
- Bert Van den Berg
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA
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33
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Bu Z, Wang L, Kendall DA. Nucleotide binding induces changes in the oligomeric state and conformation of Sec A in a lipid environment: a small-angle neutron-scattering study. J Mol Biol 2003; 332:23-30. [PMID: 12946344 PMCID: PMC3086338 DOI: 10.1016/s0022-2836(03)00840-4] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In Escherichia coli, SecA is a large, multifunctional protein that is a vital component of the general protein secretion pathway. In its membrane-bound form it functions as the motor component of the protein translocase, perhaps through successive rounds of membrane insertion and ATP hydrolysis. To understand both the energy conversion process and translocase assembly, we have used contrast-matched, small-angle neutron-scattering (SANS) experiments to examine SecA in small unilamellar vesicles of E.coli phospholipids. In the absence of nucleotide, we observe a dimeric form of SecA with a radius of gyration comparable to that previously observed for SecA in solution. In contrast, the presence of either ADP or a non-hydrolyzable ATP analog induces conversion to a monomeric form. The larger radius of gyration for the ATP-bound relative to the ADP-bound form suggests the former has a more expanded global conformation. This is the first direct structural determination of SecA in a lipid bilayer. The SANS data indicate that nucleotide turnover can function as a switch of conformation of SecA in the membrane in a manner consistent with its proposed role in successive cycles of deep membrane penetration and release with concommitant preprotein insertion.
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34
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Duong F. Binding, activation and dissociation of the dimeric SecA ATPase at the dimeric SecYEG translocase. EMBO J 2003; 22:4375-84. [PMID: 12941690 PMCID: PMC202361 DOI: 10.1093/emboj/cdg418] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The bacterial preprotein translocase is comprised of a membrane-embedded oligomeric SecYEG structure and a cytosolic dimeric SecA ATPase. The associations within SecYEG oligomers and SecA dimers, as well as between these two domains are dynamic and reversible. Here, it is shown that a covalently linked SecYEG dimer forms a functional translocase and a high affinity binding site for monomeric and dimeric SecA in solution. The interaction between these two domains stimulates the SecA ATPase, and nucleotides modulate the affinity and ratio of SecA monomers and dimers bound to the linked SecYEG complex. During the translocation reaction, the SecA monomer remains in stable association with a SecYEG protomer and the translocating preprotein. The nucleotides and translocation-dependent changes of SecA-SecYEG associations and the SecA dimeric state may reflect important facets of the preprotein translocation reaction.
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Affiliation(s)
- Franck Duong
- Laboratoire Transports et Signalisations Cellulaires, CNRS-UMR 8619, Université de Paris XI, Bâtiment 430, Orsay 91405, France.
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35
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Koch HG, Moser M, Müller M. Signal recognition particle-dependent protein targeting, universal to all kingdoms of life. Rev Physiol Biochem Pharmacol 2003; 146:55-94. [PMID: 12605305 DOI: 10.1007/s10254-002-0002-9] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
The signal recognition particle (SRP) and its membrane-bound receptor represent a ubiquitous protein-targeting device utilized by organisms as different as bacteria and humans, archaea and plants. The unifying concept of SRP-dependent protein targeting is that SRP binds to signal sequences of newly synthesized proteins as they emerge from the ribosome. In eukaryotes this interaction arrests or retards translation elongation until SRP targets the ribosome-nascent chain complexes via the SRP receptor to the translocation channel. Such channels are present in the endoplasmic reticulum of eukaryotic cells, the thylakoids of chloroplasts, or the plasma membrane of prokaryotes. The minimal functional unit of SRP consists of a signal sequence-recognizing protein and a small RNA. The as yet most complex version is the mammalian SRP whose RNA, together with six proteinaceous subunits, undergo an intricate assembly process. The preferential substrates of SRP possess especially hydrophobic signal sequences. Interactions between SRP and its receptor, the ribosome, the signal sequence, and the target membrane are regulated by GTP hydrolysis. SRP-dependent protein targeting in bacteria and chloroplasts slightly deviate from the canonical mechanism found in eukaryotes. Pro- and eukaryotic cells harbour regulatory mechanisms to prevent a malfunction of the SRP pathway.
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Affiliation(s)
- H-G Koch
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, 79104, Freiburg, Germany.
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36
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Mori H, Tsukazaki T, Masui R, Kuramitsu S, Yokoyama S, Johnson AE, Kimura Y, Akiyama Y, Ito K. Fluorescence resonance energy transfer analysis of protein translocase. SecYE from Thermus thermophilus HB8 forms a constitutive oligomer in membranes. J Biol Chem 2003; 278:14257-64. [PMID: 12533543 DOI: 10.1074/jbc.m300230200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
SecY and SecE are the two principal translocase subunits that create a channel-like pathway for the transit of preprotein across the bacterial cytoplasmic membrane. Here we report the cloning, expression, and purification of the SecYE complex (TSecYE) from a thermophilic bacterium, Thermus thermophilus HB8. Purified TSecYE can be reconstituted into proteoliposomes that function in T. thermophilus SecA (TSecA) dependent preprotein translocation. After the mixing of TSecYE derivatives labeled with either a donor or an acceptor fluorophore during reconstitution, fluorescence resonance energy transfer experiments demonstrated that 2 or more units of TSecYE in the lipid bilayer associate to form a largely non-exchangeable oligomeric structure.
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Affiliation(s)
- Hiroyuki Mori
- Institute for Virus Research, Kyoto University, Japan
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37
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Wang HW, Chen Y, Yang H, Chen X, Duan MX, Tai PC, Sui SF. Ring-like pore structures of SecA: implication for bacterial protein-conducting channels. Proc Natl Acad Sci U S A 2003; 100:4221-6. [PMID: 12642659 PMCID: PMC153074 DOI: 10.1073/pnas.0737415100] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
SecA, an essential component of the general protein secretion pathway of bacteria, is present in Escherichia coli as soluble and membrane-integral forms. Here we show by electron microscopy that SecA assumes two characteristic forms in the presence of phospholipid monolayers: dumbbell-shaped elongated structures and ring-like pore structures. The ring-like pore structures with diameters of 8 nm and holes of 2 nm are found only in the presence of anionic phospholipids. These ring-like pore structures with larger 3- to 6-nm holes (without staining) were also observed by atomic force microscopic examination. They do not form in solution or in the presence of uncharged phosphatidylcholine. These ring-like phospholipid-induced pore-structures may form the core of bacterial protein-conducting channels through bacterial membranes.
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Affiliation(s)
- Hong-Wei Wang
- Department of Biological Sciences and Biotechnology, State-Key Laboratory of Biomembranes, Tsinghua University, Beijing 100084, China
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38
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Matsuo E, Mori H, Ito K. Interfering mutations provide in vivo evidence that Escherichia coli SecE functions in multimeric states. Mol Genet Genomics 2003; 268:808-15. [PMID: 12655407 DOI: 10.1007/s00438-003-0803-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2002] [Accepted: 12/30/2002] [Indexed: 11/29/2022]
Abstract
SecY, SecE and SecG form a heterotrimer, which functions as a protein translocation channel in Escherichia coli. The cytosolic loop of SecE contains a segment that is conserved among different organisms. Here we show that mutational alterations in this segment not only inactivate the SecE function but confer dominant interfering properties on the altered SecE molecule. Such effects were especially evident in mutant cells in which the requirement for SecE function was increased. Overproduction of SecE, but not of SecY, alleviated the dominant negative effects. These results suggest that the inactive SecE molecule sequesters wild-type SecE. It was also found that an amino acid substitution, D112P, in the C-terminal periplasmic region intragenically suppressed the dominant interference. These results are consistent with a notion that there is significant SecE-SecE interaction in vivo, in which the C-terminal region has an important role. The data hence suggest that dimeric SecE participates in the formation of the functional translocation channel.
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Affiliation(s)
- E Matsuo
- Institute for Virus Research, Kyoto University, Sakyo-ku, Japan
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39
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Drew D, Fröderberg L, Baars L, de Gier JWL. Assembly and overexpression of membrane proteins in Escherichia coli. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1610:3-10. [PMID: 12586374 DOI: 10.1016/s0005-2736(02)00707-1] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The bacterium Escherichia coli is one of the most popular model systems to study the assembly of membrane proteins of the so-called helix-bundle class. Here, based on this system, we review and discuss what is currently known about the assembly of these membrane proteins. In addition, we will briefly review and discuss how E. coli has been used as a vehicle for the overexpression of membrane proteins.
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Affiliation(s)
- David Drew
- Department of Biochemistry and Biophysics, Stockholm University, S-106 91 Stockholm, Sweden
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40
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Benach J, Chou YT, Fak JJ, Itkin A, Nicolae DD, Smith PC, Wittrock G, Floyd DL, Golsaz CM, Gierasch LM, Hunt JF. Phospholipid-induced monomerization and signal-peptide-induced oligomerization of SecA. J Biol Chem 2003; 278:3628-38. [PMID: 12403785 DOI: 10.1074/jbc.m205992200] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The SecA ATPase drives the processive translocation of the N terminus of secreted proteins through the cytoplasmic membrane in eubacteria via cycles of binding and release from the SecYEG translocon coupled to ATP turnover. SecA forms a physiological dimer with a dissociation constant that has previously been shown to vary with temperature and ionic strength. We now present data showing that the oligomeric state of SecA in solution is altered by ligands that it interacts with during protein translocation. Analytical ultracentrifugation, chemical cross-linking, and fluorescence anisotropy measurements show that the physiological dimer of SecA is monomerized by long-chain phospholipid analogues. Addition of wild-type but not mutant signal sequence peptide to these SecA monomers redimerizes the protein. Physiological dimers of SecA do not change their oligomeric state when they bind signal sequence peptide in the compact, low temperature conformational state but polymerize when they bind the peptide in the domain-dissociated, high-temperature conformational state that interacts with SecYEG. This last result shows that, at least under some conditions, signal peptide interactions drive formation of new intermolecular contacts distinct from those stabilizing the physiological dimer. The observations that signal peptides promote conformationally specific oligomerization of SecA while phospholipids promote subunit dissociation suggest that the oligomeric state of SecA could change dynamically during the protein translocation reaction. Cycles of SecA subunit recruitment and dissociation could potentially be employed to achieve processivity in polypeptide transport.
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Affiliation(s)
- Jordi Benach
- Department of Biological Sciences, Columbia University, New York, New York 10027, USA
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41
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Cao TB, Saier MH. The general protein secretory pathway: phylogenetic analyses leading to evolutionary conclusions. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1609:115-25. [PMID: 12507766 DOI: 10.1016/s0005-2736(02)00662-4] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We have identified all homologues in the current databases of the ubiquitous protein constituents of the general secretory (Sec) pathway. These prokaryotic/eukaryotic proteins include (1) SecY/Sec61alpha, (2) SecE/Sec61gamma, (3) SecG/Sec61beta, (4) Ffh/SRP54 and (5) FtsY/SRP receptor subunit-alpha. Phylogenetic and sequence analyses lead to major conclusions concerning (1) the ubiquity of these proteins in living organisms, (2) the topological uniformity of some but not other Sec constituents, (3) the orthologous nature of almost all of them, (4) a total lack of paralogues in almost all organisms for which complete genome sequences are available, (5) the occurrence of two or even three paralogues in a few bacteria, plants, and yeast, depending on the Sec constituent, and (6) a tremendous degree of sequence divergence in bacteria compared with that in archaea or eukaryotes. The phylogenetic analyses lead to the conclusion that with a few possible exceptions, the five families of Sec constituents analyzed generally underwent sequence divergence in parallel but at different characteristic rates. The results provide evolutionary insights as well as guides for future functional studies. Because every organism with a fully sequenced genome exhibits at least one orthologue of each of these Sec proteins, we conclude that all living organisms have relied on the Sec system as their primary protein secretory/membrane insertion system. Because most prokaryotes and many eukaryotes encode within their genomes only one of each constituent, we also conclude that strong evolutionary pressure has minimized gene duplication events leading to the establishment of Sec paralogues. Finally, the sequence diversity of bacterial proteins as compared with their archaeal and eukaryotic counterparts is in agreement with the suggestion that bacteria were the evolutionary predecessors of archaea and eukaryotes.
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Affiliation(s)
- Thien B Cao
- Division of Biology, University of California at San Diego, La Jolla, CA 92093-0116, USA
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42
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Klostermann E, Droste Gen Helling I, Carde JP, Schünemann D. The thylakoid membrane protein ALB3 associates with the cpSecY-translocase in Arabidopsis thaliana. Biochem J 2002; 368:777-81. [PMID: 12217076 PMCID: PMC1223031 DOI: 10.1042/bj20021291] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2002] [Revised: 09/04/2002] [Accepted: 09/09/2002] [Indexed: 12/31/2022]
Abstract
The integration of light-harvesting chlorophyll proteins (LHCPs) into the thylakoid membrane requires the integral thylakoid membrane protein ALB3, a homologue of the bacterial cytoplasmic membrane protein YidC. In bacteria, YidC is associated with the SecY-translocase and facilitates the integration of Sec-dependent proteins into the plasma membrane. In addition, it is also involved in the insertion of Sec-independent proteins. In the present study we demonstrate, in Arabidopsis thaliana, that most ALB3 is a constituent of an oligomeric complex of approx. 180 kDa. In addition, we detected ALB3 in several higher-molecular-mass complexes (up to 700 kDa). Furthermore, we show that most ALB3 co-fractionates with cpSecY during gel-filtration analysis and blue native gel electrophoresis, suggesting an association of ALB3 with the cpSecY complex. A direct interaction of ALB3 with the cpSecY complex was demonstrated by co-immunoprecipitation experiments using digitonin-solubilized thylakoid membrane proteins and anti-cpSecY or anti-ALB3 antibodies. This result was further confirmed by electron microscopic co-immunolocalization of ALB3 and cpSecY. In addition, an association of ALB3 with the cpSecY complex was demonstrated directly by cross-linking experiments using the chemical cross-linker disuccinimidyl suberate.
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Affiliation(s)
- Eva Klostermann
- Institut für Biologie III der RWTH Aachen, Worringerweg 1, 52074 Aachen, Germany
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43
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Khatib K, Belin D. A novel class of secA alleles that exert a signal-sequence-dependent effect on protein export in Escherichia coli. Genetics 2002; 162:1031-43. [PMID: 12454053 PMCID: PMC1462312 DOI: 10.1093/genetics/162.3.1031] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The murine plasminogen activator inhibitor 2 (PAI2) signal sequence inefficiently promotes the export of E. coli alkaline phosphatase (AP). High-level expression of PAI2::AP chimeric proteins from the arabinose P(BAD) promoter is toxic and confers an Ara(S) phenotype. Most Ara(R) suppressors map to secA, as determined by sequencing 21 independent alleles. Mutations occur throughout the gene, including both nucleotide binding domains (NBDI and NBDII) and the putative signal sequence binding domain (SSBD). Using malE and phoA signal sequence mutants, we showed that the vast majority of these secA suppressors exhibit weak Sec phenotypes. Eight of these secA mutations were further characterized in detail. Phenotypically, these eight suppressors can be divided into three groups, each localized to one domain of SecA. Most mutations allow near-normal levels of wild-type preprotein export, but they enhance the secretion defect conferred by signal sequence mutations. Interestingly, one group exerts a selective effect on the export of PAI2::AP when compared to that of AP. In conclusion, this novel class of secA mutations, selected as suppressors of a toxic signal sequence, differs from the classical secA (prlD) mutations, selected as suppressors of defective signal sequences, although both types of mutations affect signal sequence recognition.
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Affiliation(s)
- Karim Khatib
- Department of Pathology, University of Geneva, Switzerland
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44
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Veenendaal AKJ, Van Der Does C, Driessen AJM. The core of the bacterial translocase harbors a tilted transmembrane segment 3 of SecE. J Biol Chem 2002; 277:36640-5. [PMID: 12138117 DOI: 10.1074/jbc.m205713200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The bacterial translocase mediates the translocation and membrane integration of proteins. The integral membrane proteins SecY and SecE are conserved core subunits of the translocase. Previous cysteine-scanning studies showed that the transmembrane segment (TMS) 3 of SecE contacts TMS 2 and 7 of SecY, and TMS 3 of another SecE. We now demonstrate that SecE also contacts TMS 10 of SecY. Combining all available cysteine-scanning mutagenesis data, a three-dimensional model has been built in which the positions of the helices that form the central core of the bacterial translocase are mapped. Remarkably, this model reveals that TMS 3 of SecE is strongly tilted relative to SecY.
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Affiliation(s)
- Andreas K J Veenendaal
- Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands
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45
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van der Sluis EO, Nouwen N, Driessen AJM. SecY-SecY and SecY-SecG contacts revealed by site-specific crosslinking. FEBS Lett 2002; 527:159-65. [PMID: 12220653 DOI: 10.1016/s0014-5793(02)03202-7] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Protein translocation across the cytoplasmic membrane of Escherichia coli is mediated by the integral membrane complex SecYEG and the peripherally bound ATPase SecA. To probe the environment of the cytoplasmic domains of SecY within the SecYEG complex, we introduced single cysteine residues in each of the six cytoplasmic domains. Neighbouring SecY molecules with a single cysteine residue in cytoplasmic domains C1, C2 or C6 formed a disulfide bond upon oxidation. The presence of the disulfide bond between two C2 domains reversibly inhibited protein translocation. Chemical crosslinking showed that the C2 and C3 domains are in close proximity of SecG and chemical modification of the cysteine residue in the C5 domain with N-ethyl-maleimide or fluorescein-5-maleimide inactivates the SecYEG complex. Taken together, our data give novel insights in the interactions between subunits of the SecYEG complex and emphasise the importance of cytoplasmic domain C5 for SecY functioning.
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Affiliation(s)
- Eli O van der Sluis
- Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN, Haren, The Netherlands
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46
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Steiner JM, Köcher T, Nagy C, Löffelhardt W. Chloroplast SecE: evidence for spontaneous insertion into the thylakoid membrane. Biochem Biophys Res Commun 2002; 293:747-52. [PMID: 12054533 DOI: 10.1016/s0006-291x(02)00285-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
SecE, an essential component of the bacterial SecAYEG translocase, mediates protein translocation across the cytoplasmic membrane. In the thylakoid membranes of chloroplasts an SecE homologue, cpSecE, has recently been identified. In this report we show that insertion of cpSecE does not require stromal extract, indicating that signal recognition particle is not involved. Removal of nucleoside triphosphates has apparently no effect on the integration, again ruling out an involvement of SRP or its partner protein, FtsY. The use of well-known inhibitors of the Sec- and Tat pathways, sodium azide and nigericin, respectively, also had no influence on membrane insertion. The data presented here point towards cpSecE as another passenger of a wholly spontaneous import/insertion pathway in the thylakoids of chloroplasts.
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Affiliation(s)
- Jürgen M Steiner
- Institut für Biochemie und Molekulare Zellbiologie der Universität Wien, Ludwig-Boltzmann-Forschungsstelle für Biochemie, Dr. Bohrgasse 9, A-1030 Vienna, Austria
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47
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Bessonneau P, Besson V, Collinson I, Duong F. The SecYEG preprotein translocation channel is a conformationally dynamic and dimeric structure. EMBO J 2002; 21:995-1003. [PMID: 11867527 PMCID: PMC125904 DOI: 10.1093/emboj/21.5.995] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Escherichia coli preprotein translocase comprises a membrane-embedded trimeric complex of SecY, SecE and SecG. Previous studies have shown that this complex forms ring-like assemblies, which are thought to represent the preprotein translocation channel across the membrane. We have analyzed the functional state and the quaternary structure of the SecYEG translocase by employing cross-linking and blue native gel electrophoresis. The results show that the SecYEG monomer is a highly dynamic structure, spontaneously and reversibly associating into dimers. SecG-dependent tetramers and higher order SecYEG multimers can also exist in the membrane, but these structures form at high SecYEG concentration or upon overproduction of the complex only. The translocation process does not affect the oligomeric state of the translocase and arrested preproteins can be trapped with SecYEG or SecYE dimers. Dissociation of the dimer into a monomer by detergent induces release of the trapped preprotein. These results provide direct evidence that preproteins cross the bacterial membrane, associated with a translocation channel formed by a dimer of SecYEG.
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Affiliation(s)
| | | | - Ian Collinson
- Laboratoire Transports et Signalisations Cellulaires, IBBMC-CNRS UMR 8619, Université de Paris XI, Bâtiment 430, Orsay 91405, France and
Department of Structural Biology, Max-Planck Institut für Biophysik, D-60528 Frankfurt, Germany Corresponding author e-mail:
| | - Franck Duong
- Laboratoire Transports et Signalisations Cellulaires, IBBMC-CNRS UMR 8619, Université de Paris XI, Bâtiment 430, Orsay 91405, France and
Department of Structural Biology, Max-Planck Institut für Biophysik, D-60528 Frankfurt, Germany Corresponding author e-mail:
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48
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Dempsey BR, Economou A, Dunn SD, Shilton BH. The ATPase domain of SecA can form a tetramer in solution. J Mol Biol 2002; 315:831-43. [PMID: 11812151 DOI: 10.1006/jmbi.2001.5279] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Preprotein translocase is a general and essential system for bacterial protein export, the minimal components of which are SecA and SecYEG. SecA is a peripheral ATPase that associates with nucleotide, preprotein, and the membrane integral SecYEG to form a translocation-competent complex. SecA can be separated into two domains: an N-terminal 68 kDa ATPase domain (N68) that binds preprotein and catalyzes ATP hydrolysis, and a 34 kDa C-terminal domain that regulates the ATPase activity of N68 and mediates dimerization. We have carried out gel filtration chromatography, analytical ultracentrifugation, and small-angle X-ray scattering (SAXS) to demonstrate that isolated N68 self-associates to form a tetramer in solution, indicating that removal of the C-terminal domain facilitates the formation of a higher-order SecA structure. The associative process is best modelled as a monomer-tetramer equilibrium, with a K(D) value of 63 microM(3) (where K(D)=[monomer](4)/[tetramer]) so that at moderate concentrations (10 microM and above), the tetramer is the major species in solution. Hydrodynamic properties of the N68 monomer indicate that it is almost globular in shape, but the N68 tetramer has a more ellipsoidal structure. Analysis of SAXS data indicates that the N68 tetramer is a flattened, bi-lobed structure with dimensions of approximately 13.5 nm x 9.0 nm x 6.5 nm, that appears to contain a central pore.
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Affiliation(s)
- Brian R Dempsey
- Department of Biochemistry, University of Western Ontario, London, ON N6A 5C1, Canada
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49
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Abstract
The Sec machinery (or translocase) provides a major pathway of protein translocation from the cytosol across the cytoplasmic membrane in bacteria. The SecA ATPase interacts dynamically with the SecYEG integral membrane components to drive the transmembrane movement of newly synthesized preproteins. This pathway is also used for integration of some membrane proteins and the Sec translocase interacts with other cellular components to achieve its cellular roles. The detailed protein interactions involved in these processes are being actively studied and a structural understanding of the protein-conducting channel has started to emerge.
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Affiliation(s)
- H Mori
- Institute for Virus Research, Kyoto University, Kyoto 606-8507, Japan
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50
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Legate KR, Andrews DW. Assembly strategies and GTPase regulation of the eukaryotic and Escherichia coli translocons. Biochem Cell Biol 2001. [DOI: 10.1139/o01-140] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The translocation of most proteins across the endoplasmic reticulum or bacterial inner membrane occurs through an aqueous pore that spans the membrane. Substrates that are translocated co-translationally across the membrane are directed to the translocation pore via an interaction between the cytosolic signal recognition particle and its membrane-bound receptor. Together the translocation pore and the receptor are referred to as a translocon. By studying the biogenesis of the translocon a number of alternate targeting and membrane-integration pathways have been discovered that operate independently of the signal recognition particle (SRP) pathway. The novel assembly strategies of the translocon and the ways in which these components interact to ensure the fidelity and unidirectionality of the targeting and translocation process are reviewed here.Key words: protein translocation, translocon, SRP receptor, GTPases.
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