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Yeter-Alat H, Belgareh-Touzé N, Le Saux A, Huvelle E, Mokdadi M, Banroques J, Tanner NK. The RNA Helicase Ded1 from Yeast Is Associated with the Signal Recognition Particle and Is Regulated by SRP21. Molecules 2024; 29:2944. [PMID: 38931009 PMCID: PMC11206880 DOI: 10.3390/molecules29122944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2024] [Revised: 06/12/2024] [Accepted: 06/18/2024] [Indexed: 06/28/2024] Open
Abstract
The DEAD-box RNA helicase Ded1 is an essential yeast protein involved in translation initiation that belongs to the DDX3 subfamily. The purified Ded1 protein is an ATP-dependent RNA-binding protein and an RNA-dependent ATPase, but it was previously found to lack substrate specificity and enzymatic regulation. Here we demonstrate through yeast genetics, yeast extract pull-down experiments, in situ localization, and in vitro biochemical approaches that Ded1 is associated with, and regulated by, the signal recognition particle (SRP), which is a universally conserved ribonucleoprotein complex required for the co-translational translocation of polypeptides into the endoplasmic reticulum lumen and membrane. Ded1 is physically associated with SRP components in vivo and in vitro. Ded1 is genetically linked with SRP proteins. Finally, the enzymatic activity of Ded1 is inhibited by SRP21 in the presence of SCR1 RNA. We propose a model where Ded1 actively participates in the translocation of proteins during translation. Our results provide a new understanding of the role of Ded1 during translation.
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Affiliation(s)
- Hilal Yeter-Alat
- Expression Génétique Microbienne, UMR8261 CNRS, Université de Paris, 13 rue Pierre et Marie Curie, 75005 Paris, France; (H.Y.-A.); (A.L.S.); (E.H.); (M.M.); (J.B.)
- Expression Génétique Microbienne, Institut de Biologie Physico-Chimique, Paris Sciences et Lettres University, 75005 Paris, France
| | - Naïma Belgareh-Touzé
- Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, UMR8226 CNRS, Sorbonne Université, 13 rue Pierre et Marie Curie, 75005 Paris, France;
| | - Agnès Le Saux
- Expression Génétique Microbienne, UMR8261 CNRS, Université de Paris, 13 rue Pierre et Marie Curie, 75005 Paris, France; (H.Y.-A.); (A.L.S.); (E.H.); (M.M.); (J.B.)
- Expression Génétique Microbienne, Institut de Biologie Physico-Chimique, Paris Sciences et Lettres University, 75005 Paris, France
| | - Emmeline Huvelle
- Expression Génétique Microbienne, UMR8261 CNRS, Université de Paris, 13 rue Pierre et Marie Curie, 75005 Paris, France; (H.Y.-A.); (A.L.S.); (E.H.); (M.M.); (J.B.)
- Expression Génétique Microbienne, Institut de Biologie Physico-Chimique, Paris Sciences et Lettres University, 75005 Paris, France
| | - Molka Mokdadi
- Expression Génétique Microbienne, UMR8261 CNRS, Université de Paris, 13 rue Pierre et Marie Curie, 75005 Paris, France; (H.Y.-A.); (A.L.S.); (E.H.); (M.M.); (J.B.)
- Expression Génétique Microbienne, Institut de Biologie Physico-Chimique, Paris Sciences et Lettres University, 75005 Paris, France
- Laboratory of Molecular Epidemiology and Experimental Pathology, LR16IPT04, Institut Pasteur de Tunis, Université de Tunis El Manar, Tunis 1002, Tunisia
- Institut National des Sciences Appliquées et Technologies, Université de Carthage, Tunis 1080, Tunisia
| | - Josette Banroques
- Expression Génétique Microbienne, UMR8261 CNRS, Université de Paris, 13 rue Pierre et Marie Curie, 75005 Paris, France; (H.Y.-A.); (A.L.S.); (E.H.); (M.M.); (J.B.)
- Expression Génétique Microbienne, Institut de Biologie Physico-Chimique, Paris Sciences et Lettres University, 75005 Paris, France
| | - N. Kyle Tanner
- Expression Génétique Microbienne, UMR8261 CNRS, Université de Paris, 13 rue Pierre et Marie Curie, 75005 Paris, France; (H.Y.-A.); (A.L.S.); (E.H.); (M.M.); (J.B.)
- Expression Génétique Microbienne, Institut de Biologie Physico-Chimique, Paris Sciences et Lettres University, 75005 Paris, France
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2
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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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3
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Park M, Yoo G, Bong JH, Jose J, Kang MJ, Pyun JC. Isolation and characterization of the outer membrane of Escherichia coli with autodisplayed Z-domains. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:842-7. [DOI: 10.1016/j.bbamem.2014.12.011] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Revised: 12/03/2014] [Accepted: 12/09/2014] [Indexed: 10/24/2022]
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4
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Chatzi KE, Sardis MF, Economou A, Karamanou S. SecA-mediated targeting and translocation of secretory proteins. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:1466-74. [PMID: 24583121 DOI: 10.1016/j.bbamcr.2014.02.014] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Revised: 02/12/2014] [Accepted: 02/15/2014] [Indexed: 11/26/2022]
Abstract
More than 30 years of research have revealed that the dynamic nanomotor SecA is a central player in bacterial protein secretion. SecA associates with the SecYEG channel and transports polypeptides post-translationally to the trans side of the cytoplasmic membrane. It comprises a helicase-like ATPase core coupled to two domains that provide specificity for preprotein translocation. Apart from SecYEG, SecA associates with multiple ligands like ribosomes, nucleotides, lipids, chaperones and preproteins. It exerts its essential contribution in two phases. First, SecA, alone or in concert with chaperones, helps mediate the targeting of the secretory proteins from the ribosome to the membrane. Next, at the membrane it converts chemical energy to mechanical work and translocates preproteins through the SecYEG channel. SecA is a highly dynamic enzyme, it exploits disorder-order kinetics, swiveling and dissociation of domains and dimer to monomer transformations that are tightly coupled with its catalytic function. Preprotein signal sequences and mature domains exploit these dynamics to manipulate the nanomotor and thus achieve their export at the expense of metabolic energy. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey.
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Affiliation(s)
- Katerina E Chatzi
- Institute of Molecular Biology and Biotechnology, FORTH, University of Crete, PO Box 1385, GR-711 10 Iraklio, Crete, Greece; KU Leuven, Rega Institute for Medical Research, Department of Microbiology and Immunology, Laboratory of Molecular Bacteriology, 3000 Leuven, Belgium
| | - Marios Frantzeskos Sardis
- KU Leuven, Rega Institute for Medical Research, Department of Microbiology and Immunology, Laboratory of Molecular Bacteriology, 3000 Leuven, Belgium
| | - Anastassios Economou
- Institute of Molecular Biology and Biotechnology, FORTH, University of Crete, PO Box 1385, GR-711 10 Iraklio, Crete, Greece; Department of Biology, University of Crete, PO Box 1385, GR-711 10 Iraklio, Crete, Greece; KU Leuven, Rega Institute for Medical Research, Department of Microbiology and Immunology, Laboratory of Molecular Bacteriology, 3000 Leuven, Belgium.
| | - Spyridoula Karamanou
- Institute of Molecular Biology and Biotechnology, FORTH, University of Crete, PO Box 1385, GR-711 10 Iraklio, Crete, Greece; KU Leuven, Rega Institute for Medical Research, Department of Microbiology and Immunology, Laboratory of Molecular Bacteriology, 3000 Leuven, Belgium.
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5
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Defining the Escherichia coli SecA dimer interface residues through in vivo site-specific photo-cross-linking. J Bacteriol 2013; 195:2817-25. [PMID: 23585536 DOI: 10.1128/jb.02269-12] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The motor protein SecA is a core component of the bacterial general secretory (Sec) pathway and is essential for cell viability. Despite evidence showing that SecA exists in a dynamic monomer-dimer equilibrium favoring the dimeric form in solution and in the cytoplasm, there is considerable debate as to the quaternary structural organization of the SecA dimer. Here, a site-directed photo-cross-linking technique was utilized to identify residues on the Escherichia coli SecA (ecSecA) dimer interface in the cytosol of intact cells. The feasibility of this method was demonstrated with residue Leu6, which is essential for ecSecA dimerization based on our analytical ultracentrifugation studies of SecA L6A and shown to form the cross-linked SecA dimer in vivo with p-benzoyl-phenylalanine (pBpa) substituted at position 6. Subsequently, the amino terminus (residues 2 to 11) in the nucleotide binding domain (NBD), Phe263 in the preprotein binding domain (PBD), and Tyr794 and Arg805 in the intramolecular regulator of the ATPase 1 domain (IRA1) were identified to be involved in ecSecA dimerization. Furthermore, the incorporation of pBpa at position 805 did not form a cross-linked dimer in the SecA Δ2-11 context, indicating the possibility that the amino terminus may directly contact Arg805 or that the deletion of residues 2 to 11 alters the topology of the naturally occurring ecSecA dimer.
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6
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Nithianantham S, Shilton BH. Analysis of the isolated SecA DEAD motor suggests a mechanism for chemical-mechanical coupling. J Mol Biol 2008; 383:380-9. [PMID: 18761349 DOI: 10.1016/j.jmb.2008.08.022] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2008] [Revised: 08/07/2008] [Accepted: 08/11/2008] [Indexed: 11/18/2022]
Abstract
The preprotein cross-linking domain and C-terminal domains of Escherichia coli SecA were removed to create a minimal DEAD motor, SecA-DM. SecA-DM hydrolyzes ATP and has the same affinity for ADP as full-length SecA. The crystal structure of SecA-DM in complex with ADP was solved and shows the DEAD motor in a closed conformation. Comparison with the structure of the E. coli DEAD motor in an open conformation (Protein Data Bank ID 2FSI) indicates main-chain conformational changes in two critical sequences corresponding to Motif III and Motif V of the DEAD helicase family. The structures that the Motif III and Motif V sequences adopt in the DEAD motor open conformation are incompatible with the closed conformation. Therefore, when the DEAD motor makes the transition from open to closed, Motif III and Motif V are forced to change their conformations, which likely functions to regulate passage through the transition state for ATP hydrolysis. The transition state for ATP hydrolysis for the SecA DEAD motor was modeled based on the conformation of the Vasa helicase in complex with adenylyl imidodiphosphate and RNA (Protein Data Bank ID 2DB3). A mechanism for chemical-mechanical coupling emerges, where passage through the transition state for ATP hydrolysis is hindered by the conformational changes required in Motif III and Motif V, and may be promoted by binding interactions with the preprotein substrate and/or other translocase domains and subunits.
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Affiliation(s)
- Stanley Nithianantham
- Department of Biochemistry, The University of Western Ontario, London, Ontario, Canada N6A 5C1
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7
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Abstract
The conserved protein-conducting channel, referred to as the Sec61 channel in eukaryotes or the SecY channel in eubacteria and archaea, translocates proteins across cellular membranes and integrates proteins containing hydrophobic transmembrane segments into lipid bilayers. Structural studies illustrate how the protein-conducting channel accomplishes these tasks. Three different mechanisms, each requiring a different set of channel binding partners, are employed to move polypeptide substrates: The ribosome feeds the polypeptide chain directly into the channel, a ratcheting mechanism is used by the eukaryotic endoplasmic reticulum chaperone BiP, and a pushing mechanism is utilized by the bacterial ATPase SecA. We review these translocation mechanisms, relating biochemical and genetic observations to the structures of the protein-conducting channel and its binding partners.
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Affiliation(s)
- Andrew R Osborne
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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8
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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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9
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Vrontou E, Economou A. Structure and function of SecA, the preprotein translocase nanomotor. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2005; 1694:67-80. [PMID: 15546658 DOI: 10.1016/j.bbamcr.2004.06.003] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2003] [Revised: 06/03/2004] [Accepted: 06/17/2004] [Indexed: 11/22/2022]
Abstract
Most secretory proteins that are destined for the periplasm or the outer membrane are exported through the bacterial plasma membrane by the Sec translocase. Translocase is a complex nanomachine that moves processively along its aminoacyl polymeric substrates effectively pumping them to the periplasmic space. The salient features of this process are: (a) a membrane-embedded "clamp" formed by the trimeric SecYEG protein, (b) a "motor" provided by the dimeric SecA ATPase, (c) regulatory subunits that optimize catalysis and (d) both chemical and electrochemical metabolic energy. Significant recent strides have allowed structural, biochemical and biophysical dissection of the export reaction. A model incorporating stepwise strokes of the translocase nanomachine at work is discussed.
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Affiliation(s)
- Eleftheria Vrontou
- Laboratory Unicellular, Organisms Group, Institute of Molecular Biology and Biotechnology, FO.R.T.H. and Department of Biology, University of Crete, Vassilika Vouton, P.O. Box 1527, GR-711 10 Iraklio, Crete, Greece
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10
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Papanikou E, Karamanou S, Baud C, Sianidis G, Frank M, Economou A. Helicase Motif III in SecA is essential for coupling preprotein binding to translocation ATPase. EMBO Rep 2004; 5:807-11. [PMID: 15272299 PMCID: PMC1299117 DOI: 10.1038/sj.embor.7400206] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2004] [Revised: 06/22/2004] [Accepted: 06/22/2004] [Indexed: 11/09/2022] Open
Abstract
The SecA ATPase is a protein translocase motor and a superfamily 2 (SF2) RNA helicase. The ATPase catalytic core ('DEAD motor') contains the seven conserved SF2 motifs. Here, we demonstrate that Motif III is essential for SecA-mediated protein translocation and viability. SecA Motif III mutants can bind ligands (nucleotide, the SecYEG translocase 'channel', signal and mature preprotein domains), can catalyse basal and SecYEG-stimulated ATP hydrolysis and can be activated for catalysis. However, Motif III mutation specifically blocks the preprotein-stimulated 'translocation ATPase' at a step of the reaction pathway that lies downstream of ligand binding. A functional Motif III is required for optimal ligand-driven conformational changes and kinetic parameters that underlie optimal preprotein-modulated nucleotide cycling at the SecA DEAD motor. We propose that helicase Motif III couples preprotein binding to the SecA translocation ATPase and that catalytic activation of SF2 enzymes through Motif-III-mediated action is essential for both polypeptide and nucleic-acid substrates.
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Affiliation(s)
- Efrosyni Papanikou
- Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology Hellas and Department of Biology, University of Crete, PO Box 1527, GR711 10 Iraklio, Crete, Greece
| | - Spyridoula Karamanou
- Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology Hellas and Department of Biology, University of Crete, PO Box 1527, GR711 10 Iraklio, Crete, Greece
| | - Catherine Baud
- Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology Hellas and Department of Biology, University of Crete, PO Box 1527, GR711 10 Iraklio, Crete, Greece
| | - Giorgos Sianidis
- Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology Hellas and Department of Biology, University of Crete, PO Box 1527, GR711 10 Iraklio, Crete, Greece
| | - Miriam Frank
- Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology Hellas and Department of Biology, University of Crete, PO Box 1527, GR711 10 Iraklio, Crete, Greece
| | - Anastassios Economou
- Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology Hellas and Department of Biology, University of Crete, PO Box 1527, GR711 10 Iraklio, Crete, Greece
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11
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Osborne AR, Clemons WM, Rapoport TA. A large conformational change of the translocation ATPase SecA. Proc Natl Acad Sci U S A 2004; 101:10937-42. [PMID: 15256599 PMCID: PMC491988 DOI: 10.1073/pnas.0401742101] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2004] [Indexed: 11/18/2022] Open
Abstract
The ATPase SecA mediates the posttranslational translocation of a wide range of polypeptide substrates through the SecY channel in the cytoplasmic membrane of bacteria. We have determined the crystal structure of a monomeric form of Bacillus subtilis SecA at a 2.2-A resolution. A comparison with the previously determined structures of SecA reveals a nucleotide-independent, large conformational change that opens a deep groove similar to that in other proteins that interact with diverse polypeptides. We propose that the open form of SecA represents an activated state.
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Affiliation(s)
- Andrew R Osborne
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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12
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El-Fahmawi B, Owttrim GW. Polar-biased localization of the cold stress-induced RNA helicase, CrhC, in the Cyanobacterium Anabaena sp. strain PCC 7120. Mol Microbiol 2003; 50:1439-48. [PMID: 14622428 DOI: 10.1046/j.1365-2958.2003.03783.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Shift of the filamentous cyanobacterium, Anabaena sp. strain PCC 7120, from 30 degrees C to 20 degrees C induces expression of a cold shock response gene encoding the RNA helicase CrhC. Subcellular localization using cellular fractionation and membrane purification indicated that CrhC is localized to the plasma membrane with no evidence of a soluble-cytoplasmic form. Treatment of spheroplasts with trypsin and membrane fractions with various denaturing agents identified CrhC as an integral membrane protein associated with the cytoplasmic face of the plasma membrane. Immunoelectron microscopy confirmed the plasma membrane association of CrhC. Interestingly, a higher specific labelling was observed at the cell poles on the septa between adjacent cells within cell filaments. On a per cell area basis, CrhC localization to the cell pole was 3.5- and >1000-fold higher than to the lateral portion of the plasma membrane or cytoplasm respectively. In addition, CrhC also localizes to new cell poles forming within a dividing cell. Polar-biased localization of the CrhC RNA helicase implies a role in RNA metabolism that is plasma membrane associated and preferentially occurs at the cell poles during cyanobacterial response to cold stress.
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Affiliation(s)
- Bassam El-Fahmawi
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9
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13
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Zito CR, Oliver D. Two-stage binding of SecA to the bacterial translocon regulates ribosome-translocon interaction. J Biol Chem 2003; 278:40640-6. [PMID: 12907673 DOI: 10.1074/jbc.m308025200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The bacterial translocon interacts with both SecA-bound preproteins and nascent chain-ribosome complexes during Sec and signal recognition particle-dependent protein translocation, respectively. In their inactive state, translocons are saturated with ribosomes and SecA protein, reflecting the inherent affinity of these components for one another. We found that SecA and ribosomes are bound simultaneously and noncompetitively to a common set of inactive translocons. Furthermore, we demonstrate that at a later stage in binding, SecA possesses a ribosome-translocon dissociation activity that is coupled to its ATP-dependent membrane insertion and retraction cycle that drives protein translocation. This novel activity is presumably important in the commitment of the translocon to the Sec-dependent pathway. These results also provide a rationale for the compatibility and regulation of multiple protein translocation pathways that each makes distinct demands on a common translocon core.
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Affiliation(s)
- Christopher R Zito
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459, USA
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14
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Or E, Navon A, Rapoport T. Dissociation of the dimeric SecA ATPase during protein translocation across the bacterial membrane. EMBO J 2002; 21:4470-9. [PMID: 12198149 PMCID: PMC126201 DOI: 10.1093/emboj/cdf471] [Citation(s) in RCA: 136] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The ATPase SecA mediates post-translational translocation of precursor proteins through the SecYEG channel of the bacterial inner membrane. We show that SecA, up to now considered to be a stable dimer, is actually in equilibrium with a small fraction of monomers. In the presence of membranes containing acidic phospholipids or in certain detergents, SecA completely dissociates into monomers. A synthetic signal peptide also affects dissociation into monomers. In addition, conversion into the monomeric state can be achieved by mutating a small number of residues in a dimeric and fully functional SecA fragment. This monomeric SecA fragment still maintains strong binding to SecYEG in the membrane as well as significant in vitro translocation activity. Together, the data suggest that the SecA dimer dissociates during protein translocation. Since SecA contains all characteristic motifs of a certain class of monomeric helicases, and since mutations in residues shared with the helicases abolish its translocation activity, SecA may function in a similar manner.
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Affiliation(s)
| | | | - Tom Rapoport
- Department of Cell Biology, Harvard Medical School, HHMI, Boston, MA 02115, USA
Corresponding author e-mail:
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15
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Sarker S, Oliver D. Critical regions of secM that control its translation and secretion and promote secretion-specific secA regulation. J Bacteriol 2002; 184:2360-9. [PMID: 11948148 PMCID: PMC134986 DOI: 10.1128/jb.184.9.2360-2369.2002] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
SecA is an essential ATP-driven motor protein that binds to presecretory or membrane proteins and the translocon and promotes the translocation or membrane integration of these proteins. secA is subject to a protein secretion-specific form of regulation, whereby its translation is elevated during secretion-limiting conditions. A novel mechanism that promotes this regulation involves translational pausing within the gene upstream of secA, secM. The secM translational pause prevents formation of an RNA helix that normally blocks secA translational initiation. The duration of this pause is controlled by the rate of secretion of nascent SecM, which in turn depends on its signal peptide and a functional translocon. We characterized the atypical secM signal peptide and found that mutations within the amino-terminal region specifically affect the secM translational pause and secA regulation, while mutations in the hydrophobic core region affect SecM secretion as well as translational pausing and secA regulation. In addition, mutational analysis of the 3' end of secM allowed us to identify a conserved region that is required to promote the translational pause that appears to be operative at the peptide level. Together, our results provide direct support for the secM translational pause model of secA regulation, and they pinpoint key sequences within secM that promote this important regulatory system.
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Affiliation(s)
- Shameema Sarker
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459, USA
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Anantharaman V, Koonin EV, Aravind L. Comparative genomics and evolution of proteins involved in RNA metabolism. Nucleic Acids Res 2002; 30:1427-64. [PMID: 11917006 PMCID: PMC101826 DOI: 10.1093/nar/30.7.1427] [Citation(s) in RCA: 381] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
RNA metabolism, broadly defined as the compendium of all processes that involve RNA, including transcription, processing and modification of transcripts, translation, RNA degradation and its regulation, is the central and most evolutionarily conserved part of cell physiology. A comprehensive, genome-wide census of all enzymatic and non-enzymatic protein domains involved in RNA metabolism was conducted by using sequence profile analysis and structural comparisons. Proteins related to RNA metabolism comprise from 3 to 11% of the complete protein repertoire in bacteria, archaea and eukaryotes, with the greatest fraction seen in parasitic bacteria with small genomes. Approximately one-half of protein domains involved in RNA metabolism are present in most, if not all, species from all three primary kingdoms and are traceable to the last universal common ancestor (LUCA). The principal features of LUCA's RNA metabolism system were reconstructed by parsimony-based evolutionary analysis of all relevant groups of orthologous proteins. This reconstruction shows that LUCA possessed not only the basal translation system, but also the principal forms of RNA modification, such as methylation, pseudouridylation and thiouridylation, as well as simple mechanisms for polyadenylation and RNA degradation. Some of these ancient domains form paralogous groups whose evolution can be traced back in time beyond LUCA, towards low-specificity proteins, which probably functioned as cofactors for ribozymes within the RNA world framework. The main lineage-specific innovations of RNA metabolism systems were identified. The most notable phase of innovation in RNA metabolism coincides with the advent of eukaryotes and was brought about by the merge of the archaeal and bacterial systems via mitochondrial endosymbiosis, but also involved emergence of several new, eukaryote-specific RNA-binding domains. Subsequent, vast expansions of these domains mark the origin of alternative splicing in animals and probably in plants. In addition to the reconstruction of the evolutionary history of RNA metabolism, this analysis produced numerous functional predictions, e.g. of previously undetected enzymes of RNA modification.
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Affiliation(s)
- Vivek Anantharaman
- National Center for Biotechnology Information, National Library of Medicine, 8600 Rockville Pike, Building 389, National Institutes of Health, Bethesda, MD 20894, USA
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