1
|
Allen WJ, Corey RA, Watkins DW, Oliveira ASF, Hards K, Cook GM, Collinson I. Rate-limiting transport of positively charged arginine residues through the Sec-machinery is integral to the mechanism of protein secretion. eLife 2022; 11:77586. [PMID: 35486093 PMCID: PMC9110029 DOI: 10.7554/elife.77586] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2022] [Accepted: 04/29/2022] [Indexed: 11/24/2022] Open
Abstract
Transport of proteins across and into membranes is a fundamental biological process with the vast majority being conducted by the ubiquitous Sec machinery. In bacteria, this is usually achieved when the SecY-complex engages the cytosolic ATPase SecA (secretion) or translating ribosomes (insertion). Great strides have been made towards understanding the mechanism of protein translocation. Yet, important questions remain – notably, the nature of the individual steps that constitute transport, and how the proton-motive force (PMF) across the plasma membrane contributes. Here, we apply a recently developed high-resolution protein transport assay to explore these questions. We find that pre-protein transport is limited primarily by the diffusion of arginine residues across the membrane, particularly in the context of bulky hydrophobic sequences. This specific effect of arginine, caused by its positive charge, is mitigated for lysine which can be deprotonated and transported across the membrane in its neutral form. These observations have interesting implications for the mechanism of protein secretion, suggesting a simple mechanism through which the PMF can aid transport by enabling a 'proton ratchet', wherein re-protonation of exiting lysine residues prevents channel re-entry, biasing transport in the outward direction.
Collapse
Affiliation(s)
- William J Allen
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| | - Robin A Corey
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Daniel W Watkins
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| | | | - Kiel Hards
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
| | - Gregory M Cook
- Department of Microbiology and Immunology, University of Otago, Duneding, New Zealand
| | - Ian Collinson
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| |
Collapse
|
2
|
Electrochromic shift supports the membrane destabilization model of Tat-mediated transport and shows ion leakage during Sec transport. Proc Natl Acad Sci U S A 2021; 118:2018122118. [PMID: 33723047 DOI: 10.1073/pnas.2018122118] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The mechanism and pore architecture of the Tat complex during transport of folded substrates remain a mystery, partly due to rapid dissociation after translocation. In contrast, the proteinaceous SecY pore is a persistent structure that needs only to undergo conformational shifts between "closed" and "opened" states when translocating unfolded substrate chains. Where the proteinaceous pore model describes the SecY pore well, the toroidal pore model better accounts for the high-energy barrier that must be overcome when transporting a folded substrate through the hydrophobic bilayer in Tat transport. Membrane conductance behavior can, in principle, be used to distinguish between toroidal and proteinaceous pores, as illustrated in the examination of many antimicrobial peptides as well as mitochondrial Bax and Bid. Here, we measure the electrochromic shift (ECS) decay as a proxy for conductance in isolated thylakoids, both during protein transport and with constitutively assembled translocons. We find that membranes with the constitutively assembled Tat complex and those undergoing Tat transport display conductance characteristics similar to those of resting membranes. Membranes undergoing Sec transport and those with the substrate-engaged SecY pore result in significantly more rapid electric field decay. The responsiveness of the ECS signal in membranes with active SecY recalls the steep relationship between applied voltage and conductance in a proteinaceous pore, while the nonaccelerated electric field decay with both Tat transport and the constitutive Tat complex under the same electric field is consistent with the behavior of a toroidal pore.
Collapse
|
3
|
Abstract
Single-molecule studies provide unprecedented details about processes that are difficult to grasp by bulk biochemical assays that yield ensemble-averaged results. One of these processes is the translocation and insertion of proteins across and into the bacterial cytoplasmic membrane. This process is facilitated by the universally conserved secretion (Sec) system, a multi-subunit membrane protein complex that consists of dissociable cytoplasmic targeting components, a molecular motor, a protein-conducting membrane pore, and accessory membrane proteins. Here, we review recent insights into the mechanisms of protein translocation and membrane protein insertion from single-molecule studies.
Collapse
Affiliation(s)
- Anne-Bart Seinen
- Department of Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute; and the Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, Netherlands
- Current affiliation: Biophysics Group, AMOLF, 1098 XG Amsterdam, Netherlands
| | - Arnold J.M. Driessen
- Department of Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute; and the Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, Netherlands
| |
Collapse
|
4
|
Knyazev DG, Winter L, Bauer BW, Siligan C, Pohl P. Ion conductivity of the bacterial translocation channel SecYEG engaged in translocation. J Biol Chem 2014; 289:24611-6. [PMID: 25016015 PMCID: PMC4148884 DOI: 10.1074/jbc.m114.588491] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
While engaged in protein transport, the bacterial translocon SecYEG must maintain the membrane barrier to small ions. The preservation of the proton motif force was attributed to (i) cation exclusion, (ii) engulfment of the nascent chain by the hydrophobic pore ring, and (iii) a half-helix partly plugging the channel. In contrast, we show here that preservation of the proton motif force is due to a voltage-driven conformational change. Preprotein or signal peptide binding to the purified and reconstituted SecYEG results in large cation and anion conductivities only when the membrane potential is small. Physiological values of membrane potential close the activated channel. This voltage-dependent closure is not dependent on the presence of the plug domain and is not affected by mutation of 3 of the 6 constriction residues to glycines. Cellular ion homeostasis is not challenged by the small remaining leak conductance.
Collapse
Affiliation(s)
- Denis G Knyazev
- From the Institute of Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, A-4020 Linz, Austria
| | - Lukas Winter
- From the Institute of Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, A-4020 Linz, Austria
| | - Benedikt W Bauer
- From the Institute of Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, A-4020 Linz, Austria
| | - Christine Siligan
- From the Institute of Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, A-4020 Linz, Austria
| | - Peter Pohl
- From the Institute of Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, A-4020 Linz, Austria
| |
Collapse
|
5
|
Kedrov A, Kusters I, Driessen AJM. Single-Molecule Studies of Bacterial Protein Translocation. Biochemistry 2013; 52:6740-54. [DOI: 10.1021/bi400913x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Alexej Kedrov
- Department of Molecular Microbiology, Groningen
Biomolecular Sciences and Biotechnology Institute, and Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 7, 9747
AG Groningen, The Netherlands
| | - Ilja Kusters
- Department of Molecular Microbiology, Groningen
Biomolecular Sciences and Biotechnology Institute, and Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 7, 9747
AG Groningen, The Netherlands
| | - Arnold J. M. Driessen
- Department of Molecular Microbiology, Groningen
Biomolecular Sciences and Biotechnology Institute, and Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 7, 9747
AG Groningen, The Netherlands
| |
Collapse
|
6
|
Lin BR, Hsieh YH, Jiang C, Tai PC. Escherichia coli Membranes Depleted of SecYEG Elicit SecA-Dependent Ion-Channel Activity but Lose Signal Peptide Specificity. J Membr Biol 2012; 245:747-57. [DOI: 10.1007/s00232-012-9477-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2011] [Accepted: 06/30/2012] [Indexed: 11/29/2022]
|
7
|
Dalal K, Duong F. The SecY complex: conducting the orchestra of protein translocation. Trends Cell Biol 2011; 21:506-14. [DOI: 10.1016/j.tcb.2011.04.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2011] [Revised: 04/11/2011] [Accepted: 04/18/2011] [Indexed: 10/18/2022]
|
8
|
Preserving the membrane barrier for small molecules during bacterial protein translocation. Nature 2011; 473:239-42. [PMID: 21562565 PMCID: PMC3093665 DOI: 10.1038/nature10014] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2011] [Accepted: 03/22/2011] [Indexed: 01/03/2023]
Abstract
Many proteins are translocated through the SecY channel in bacteria and archaea and through the related Sec61 channel in eukaryotes. The channel has an hourglass shape with a narrow constriction approximately halfway across the membrane, formed by a pore ring of amino acids. While the cytoplasmic cavity of the channel is empty, the extracellular cavity is filled with a short helix called the plug, which moves out of the way during protein translocation. The mechanism by which the channel transports large polypeptides and yet prevents the passage of small molecules, such as ions or metabolites, has been controversial. Here, we have addressed this issue in intact Escherichia coli cells by testing the permeation of small molecules through wild-type and mutant SecY channels, which are either in the resting state or contain a defined translocating polypeptide chain. We show that in the resting state, the channel is sealed by both the pore ring and the plug domain. During translocation, the pore ring forms a 'gasket-like' seal around the polypeptide chain, preventing the permeation of small molecules. The structural conservation of the channel in all organisms indicates that this may be a universal mechanism by which the membrane barrier is maintained during protein translocation.
Collapse
|
9
|
Dalal K, Duong F. The SecY complex forms a channel capable of ionic discrimination. EMBO Rep 2009; 10:762-8. [PMID: 19483671 DOI: 10.1038/embor.2009.87] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2008] [Revised: 03/10/2009] [Accepted: 03/23/2009] [Indexed: 11/09/2022] Open
Abstract
Protein translocation across the bacterial membrane occurs at the SecY complex or channel. The resting SecY channel is impermeable to small molecules owing to a plug domain that creates a seal. Here, we report that a channel loosely sealed, or with a plug locked open, does not, however, lead to general membrane permeability. Instead, strong selectivity towards small monovalent anions, especially chloride, is observed. Mutations in the pore ring-structure increase both the translocation activity of the channel and its ionic conductance, however the selectivity is maintained. The same ionic specificity also occurs at the onset of protein translocation and across the archaeal SecY complex. Thus, the ion-conducting characteristic of the channel seems to be conserved as a normal consequence of protein translocation. We propose that the pore ring-structure forms a selectivity filter, allowing cells to tolerate channels with imperfect plugs.
Collapse
Affiliation(s)
- Kush Dalal
- Department of Biochemistry and Molecular Biology, Life Sciences Institute, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
| | | |
Collapse
|
10
|
Gumbart J, Schulten K. The roles of pore ring and plug in the SecY protein-conducting channel. ACTA ACUST UNITED AC 2008; 132:709-19. [PMID: 19001142 PMCID: PMC2585858 DOI: 10.1085/jgp.200810062] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The protein-conducting channel, or translocon, is an evolutionarily conserved complex that allows nascent proteins to cross a cellular membrane or integrate into it. The crystal structure of an archaeal translocon, the SecY complex, revealed that two elements contribute to sealing the channel: a small "plug" domain blocking the periplasmic region of the channel, and a pore ring composed of six hydrophobic residues acting as a constriction point at the channel's center. To determine the independent functions of these two elements, we have performed molecular dynamics simulations of the native channel as well as of two recently structurally resolved mutants in which portions of their plugs were deleted. We find that in the mutants, the instability in the plug region leads to a concomitant increase in flexibility of the pore ring. The instability is quantified by the rate of water permeation in each system as well as by the force required for oligopeptide translocation. Through a novel simulation in which the interactions between the plug and water were independently controlled, we find that the role of the plug in stabilizing the pore ring is significantly more important than its role as a purely steric barrier.
Collapse
Affiliation(s)
- James Gumbart
- Department of Physics and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | | |
Collapse
|
11
|
Rapoport TA. Protein translocation across the eukaryotic endoplasmic reticulum and bacterial plasma membranes. Nature 2008; 450:663-9. [PMID: 18046402 DOI: 10.1038/nature06384] [Citation(s) in RCA: 669] [Impact Index Per Article: 41.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A decisive step in the biosynthesis of many proteins is their partial or complete translocation across the eukaryotic endoplasmic reticulum membrane or the prokaryotic plasma membrane. Most of these proteins are translocated through a protein-conducting channel that is formed by a conserved, heterotrimeric membrane-protein complex, the Sec61 or SecY complex. Depending on channel binding partners, polypeptides are moved by different mechanisms: the polypeptide chain is transferred directly into the channel by the translating ribosome, a ratcheting mechanism is used by the endoplasmic reticulum chaperone BiP, and a pushing mechanism is used by the bacterial ATPase SecA. Structural, genetic and biochemical data show how the channel opens across the membrane, releases hydrophobic segments of membrane proteins laterally into lipid, and maintains the membrane barrier for small molecules.
Collapse
Affiliation(s)
- Tom A Rapoport
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA.
| |
Collapse
|
12
|
Bol R, de Wit JG, Driessen AJM. The Active Protein-conducting Channel of Escherichia coli Contains an Apolar Patch. J Biol Chem 2007; 282:29785-93. [PMID: 17699162 DOI: 10.1074/jbc.m702140200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein translocation across the cytoplasmic membrane of Escherichia coli is mediated by translocase, a complex of a protein-conducting channel, SecYEG, and a peripheral motor domain, SecA. SecYEG has been proposed to constitute an aqueous path for proteins to pass the membrane in an unfolded state. To probe the solvation state of the active channel, the polarity sensitive fluorophore N-((2-(iodoacetoxy)ethyl)-N-methyl) amino-7-nitrobenz-2-oxa-1,3-diazole was introduced at specific positions in the C-terminal region of the secretory protein proOmpA. Fluorescence measurements with defined proOmpA-DHFR translocation intermediates indicate mostly a water-exposed environment with a hydrophobic region in the center of the channel.
Collapse
Affiliation(s)
- Redmar Bol
- Department of Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, The Netherlands
| | | | | |
Collapse
|
13
|
Saparov SM, Erlandson K, Cannon K, Schaletzky J, Schulman S, Rapoport TA, Pohl P. Determining the conductance of the SecY protein translocation channel for small molecules. Mol Cell 2007; 26:501-9. [PMID: 17531809 DOI: 10.1016/j.molcel.2007.03.022] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2006] [Revised: 01/30/2007] [Accepted: 03/27/2007] [Indexed: 11/20/2022]
Abstract
The channel formed by the SecY complex must maintain the membrane barrier for ions and other small molecules during the translocation of membrane or secretory proteins. We have tested the permeability of the channel by using planar bilayers containing reconstituted purified E. coli SecY complex. Wild-type SecY complex did not show any conductance for ions or water. Deletion of the "plug," a short helix normally located in the center of the SecY complex, or modification of a cysteine introduced into the plug resulted in transient channel openings; a similar effect was seen with a mutation in the pore ring, a constriction in the center of the channel. Permanent channel opening occurred when the plug was moved out of the way by disulfide-bridge formation. These data show that the resting channel on its own forms a barrier for small molecules, with both the pore ring and the plug required for the seal; channel opening requires movement of the plug.
Collapse
Affiliation(s)
- Sapar M Saparov
- Institut fuer Biophysik, Johannes Kepler Universitaet Linz, Linz, Austria
| | | | | | | | | | | | | |
Collapse
|
14
|
Lin BR, Gierasch LM, Jiang C, Tai PC. Electrophysiological studies in Xenopus oocytes for the opening of Escherichia coli SecA-dependent protein-conducting channels. J Membr Biol 2007; 214:103-13. [PMID: 17530158 PMCID: PMC2896742 DOI: 10.1007/s00232-006-0079-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2006] [Revised: 11/16/2006] [Indexed: 11/25/2022]
Abstract
Protein translocation in Escherichia coli requires protein-conducting channels in cytoplasmic membranes to allow precursor peptides to pass through with adenosine triphosphate (ATP) hydrolysis. Here, we report a novel, sensitive method that detects the opening of the SecA-dependent protein-conducting channels at the nanogram level. E. coli inverted membrane vesicles were injected into Xenopus oocytes, and ionic currents were recorded using the two-electrode voltage clamp. Currents were observed only in the presence of E. coli SecA in conjunction with E. coli membranes. Observed currents showed outward rectification in the presence of KCl as permeable ions and were significantly enhanced by coinjection with the precursor protein proOmpA or active LamB signal peptide. Channel activity was blockable with sodium azide or adenylyl 5'-(beta,gamma-methylene)-diphosphonate, a nonhydrolyzable ATP analogue, both of which are known to inhibit SecA protein activity. Endogenous oocyte precursor proteins also stimulated ion current activity and can be inhibited by puromycin. In the presence of puromycin, exogenous proOmpA or LamB signal peptides continued to enhance ionic currents. Thus, the requirement of signal peptides and ATP hydrolysis for the SecA-dependent currents resembles biochemical protein translocation assay with E. coli membrane vesicles, indicating that the Xenopus oocyte system provides a sensitive assay to study the role of Sec and precursor proteins in the formation of protein-conducting channels using electrophysiological methods.
Collapse
Affiliation(s)
- Bor-Ruei Lin
- Department of Biology, Georgia State University, 24 Peachtree Center Avenue, Atlanta, GA 30303, USA
| | - Lila M. Gierasch
- Departments of Biochemistry and Molecular Biology and of Chemistry, University of Massachusetts, 710 N. Pleasant Street, Amherst, MA 01003, USA
| | - Chun Jiang
- Department of Biology, Georgia State University, 24 Peachtree Center Avenue, Atlanta, GA 30303, USA
| | - Phang C. Tai
- Department of Biology, Georgia State University, 24 Peachtree Center Avenue, Atlanta, GA 30303, USA
| |
Collapse
|
15
|
Teter SA, Theg SM. Energy-transducing thylakoid membranes remain highly impermeable to ions during protein translocation. Proc Natl Acad Sci U S A 1998; 95:1590-4. [PMID: 9465060 PMCID: PMC19107 DOI: 10.1073/pnas.95.4.1590] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
We investigated the operation of a posttranslational protein translocation pathway to determine whether ions are excluded from the translocase during protein transport. The membrane capacitance during protein translocation across chloroplast thylakoid membranes was monitored via electric-field-indicating carotenoid electrochromic bandshift measurements. Evidence is presented that shows that the membrane ion conductance is not increased during the complete cycle of binding, transport, and substrate release by the DeltapH-dependent translocase; i.e., the membrane remains ion-tight during protein translocation. We further demonstrate that a synthetic targeting peptide that directs proteins across this membrane does not gate translocation pores. We conclude that protein transport across the thylakoid membrane does not compromise its ability to maintain ion gradients and is, thus, unlikely to affect its functions in energy transduction.
Collapse
Affiliation(s)
- S A Teter
- Division of Biological Sciences, Section of Plant Biology, University of California, Davis, CA 95616, USA
| | | |
Collapse
|
16
|
Biochemical analyses of components comprising the protein translocation machinery of Escherichia coli. ACTA ACUST UNITED AC 1995. [DOI: 10.1016/s1874-5172(06)80007-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
|
17
|
Arkowitz RA, Bassilana M. Protein translocation in Escherichia coli. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1197:311-43. [PMID: 7819269 DOI: 10.1016/0304-4157(94)90012-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- R A Arkowitz
- MRC Laboratory of Molecular Biology, Cambridge, UK
| | | |
Collapse
|
18
|
|
19
|
Economou A, Wickner W. SecA promotes preprotein translocation by undergoing ATP-driven cycles of membrane insertion and deinsertion. Cell 1994; 78:835-43. [PMID: 8087850 DOI: 10.1016/s0092-8674(94)90582-7] [Citation(s) in RCA: 455] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
SecA, the peripheral subunit of E. coli preprotein translocase, alternates between a membrane inserted and a deinserted state as part of the catalytic cycle of preprotein translocation. When SecA is complexed with SecY/E and preprotein, ATP drives a profound conformational change, leading to membrane insertion of a 30 kDa domain of SecA. The inserted domain is protease-inaccessible from the cytosolic side of the membrane, but becomes accessible upon membrane disruption. Concomitant with 30 kDa domain insertion, approximately 20 aminoacyl residues of the preprotein are translocated. Additional ATP, which may be hydrolyzed at the second ATP site of SecA, releases the translocated preprotein and allows the 30 kDa domain to deinsert, whence it can exchange with cytosolic SecA. Thus, SecA is the mobile subunit of an integral membrane transporter, consuming ATP during both the insertion and deinsertion phases of its catalytic cycle while guiding preprotein segments across the membrane.
Collapse
Affiliation(s)
- A Economou
- Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755-3844
| | | |
Collapse
|
20
|
Palmen R, Driessen AJ, Hellingwerf KJ. Bioenergetic aspects of the translocation of macromolecules across bacterial membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1183:417-51. [PMID: 8286395 DOI: 10.1016/0005-2728(94)90072-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Bacteria are extremely versatile in the sense that they have gained the ability to transport all three major classes of biopolymers through their cell envelope: proteins, nucleic acids, and polysaccharides. These macromolecules are translocated across membranes in a large number of cellular processes by specific translocation systems. Members of the ABC (ATP binding cassette) superfamily of transport ATPases are involved in the translocation of all three classes of macromolecules, in addition to unique transport ATPases. An intriguing aspect of these transport processes is that the barrier function of the membrane is preserved despite the fact the dimensions of the translocated molecules by far surpasses the thickness of the membrane. This raises questions like: How are these polar compounds translocated across the hydrophobic interior of the membrane, through a proteinaceous pore or through the lipid phase; what drives these macromolecules across the membrane; which energy sources are used and how is unidirectionality achieved? It is generally believed that macromolecules are translocated in a more or less extended, most likely linear form. A recurring theme in the bioenergetics of these translocation reactions in bacteria is the joint involvement of free energy input in the form of ATP hydrolysis and via proton sym- or antiport, driven by a proton gradient. Important similarities in the bioenergetic mechanisms of the translocation of these biopolymers therefore may exist.
Collapse
Affiliation(s)
- R Palmen
- Department of Microbiology, University of Amsterdam, The Netherlands
| | | | | |
Collapse
|
21
|
Affiliation(s)
- V Géli
- Laboratoire d'Ingéniérie et de Dynamique des Systèmes Membranaires, Marseille, France
| | | |
Collapse
|
22
|
Abstract
The past year has seen significant advances in the field of protein translocation: the roles of the signal recognition particle and its receptor have been understood in greater detail; many membrane components responsible for translocation have been identified; and insight has been gained into how proteins cross membranes.
Collapse
Affiliation(s)
- S Simon
- Laboratory of Cellular Biophysics, Rockefeller University, New York, New York 10021
| |
Collapse
|
23
|
Kawasaki S, Mizushima S, Tokuda H. Membrane vesicles containing overproduced SecY and SecE exhibit high translocation ATPase activity and countermovement of protons in a SecA- and presecretory protein-dependent manner. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53081-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|