1
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Allen WJ, Collinson I. A unifying mechanism for protein transport through the core bacterial Sec machinery. Open Biol 2023; 13:230166. [PMID: 37643640 PMCID: PMC10465204 DOI: 10.1098/rsob.230166] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Accepted: 07/21/2023] [Indexed: 08/31/2023] Open
Abstract
Encapsulation and compartmentalization are fundamental to the evolution of cellular life, but they also pose a challenge: how to partition the molecules that perform biological functions-the proteins-across impermeable barriers into sub-cellular organelles, and to the outside. The solution lies in the evolution of specialized machines, translocons, found in every biological membrane, which act both as gate and gatekeeper across and into membrane bilayers. Understanding how these translocons operate at the molecular level has been a long-standing ambition of cell biology, and one that is approaching its denouement; particularly in the case of the ubiquitous Sec system. In this review, we highlight the fruits of recent game-changing technical innovations in structural biology, biophysics and biochemistry to present a largely complete mechanism for the bacterial version of the core Sec machinery. We discuss the merits of our model over alternative proposals and identify the remaining open questions. The template laid out by the study of the Sec system will be of immense value for probing the many other translocons found in diverse biological membranes, towards the ultimate goal of altering or impeding their functions for pharmaceutical or biotechnological purposes.
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Affiliation(s)
- William J. Allen
- School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK
| | - Ian Collinson
- School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK
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2
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Refined measurement of SecA-driven protein secretion reveals that translocation is indirectly coupled to ATP turnover. Proc Natl Acad Sci U S A 2020; 117:31808-31816. [PMID: 33257538 DOI: 10.1073/pnas.2010906117] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The universally conserved Sec system is the primary method cells utilize to transport proteins across membranes. Until recently, measuring the activity-a prerequisite for understanding how biological systems work-has been limited to discontinuous protein transport assays with poor time resolution or reported by large, nonnatural tags that perturb the process. The development of an assay based on a split superbright luciferase (NanoLuc) changed this. Here, we exploit this technology to unpick the steps that constitute posttranslational protein transport in bacteria. Under the conditions deployed, the transport of a model preprotein substrate (proSpy) occurs at 200 amino acids (aa) per minute, with SecA able to dissociate and rebind during transport. Prior to that, there is no evidence for a distinct, rate-limiting initiation event. Kinetic modeling suggests that SecA-driven transport activity is best described by a series of large (∼30 aa) steps, each coupled to hundreds of ATP hydrolysis events. The features we describe are consistent with a nondeterministic motor mechanism, such as a Brownian ratchet.
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3
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Comparison of Single and Multiple Turnovers of SecYEG in Escherichia coli. J Bacteriol 2020; 202:JB.00462-20. [PMID: 32989086 DOI: 10.1128/jb.00462-20] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Accepted: 09/18/2020] [Indexed: 01/01/2023] Open
Abstract
Precursor proteins are translocated across the cytoplasmic membrane in Escherichia coli by the general secretory, or Sec, pathway. The main components of the pathway are the integral membrane heterotrimeric SecYEG complex and the peripheral membrane ATPase, SecA. In this study, we have applied an in vitro assay using inverted cytoplasmic membrane vesicles to investigate the complex cycle that leads to translocation. We compared the apparent rate constants for nine precursors under two experimental conditions, single turnover and multiple turnovers. For each precursor, the rate constant for a single turnover was higher than for multiple turnovers, indicating that a different step limits the rate under the two conditions. We conclude that the rate-limiting step for a single turnover is an early step in the initial phase of transit through the channel, whereas the rate of multiple turnovers is limited by the resetting of the translocon. The presence of the chaperone SecB during multiple turnovers increased the maximal amplitude translocated for the three precursor species tested, pGBP, pPhoA, and proOmpA, and also increased the apparent rate constants for both pGBP and pPhoA. The rate constant for proOmpA was decreased by the presence of SecB.IMPORTANCE Vastly different experimental techniques and conditions have been used to study export in E. coli We demonstrated that altering experimental conditions can change the step that is observed during study. Investigators should consider specific experimental conditions when comparing data from different laboratories, as well as when comparing data from different experiments within a laboratory. We have shown that each precursor species has inherent properties that determine the translocation rate; thus generalizations from studies of a single species must be made with caution. A summary of advantages and disadvantages in use of nine precursors is presented.
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4
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Lindič N, Loboda J, Usenik A, Vidmar R, Turk D. The Structure of Clostridioides difficile SecA2 ATPase Exposes Regions Responsible for Differential Target Recognition of the SecA1 and SecA2-Dependent Systems. Int J Mol Sci 2020; 21:ijms21176153. [PMID: 32858965 PMCID: PMC7503281 DOI: 10.3390/ijms21176153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 08/22/2020] [Accepted: 08/24/2020] [Indexed: 11/17/2022] Open
Abstract
SecA protein is a major component of the general bacterial secretory system. It is an ATPase that couples nucleotide hydrolysis to protein translocation. In some Gram-positive pathogens, a second paralogue, SecA2, exports a different set of substrates, usually virulence factors. To identify SecA2 features different from SecA(1)s, we determined the crystal structure of SecA2 from Clostridioides difficile, an important nosocomial pathogen, in apo and ATP-γ-S-bound form. The structure reveals a closed monomer lacking the C-terminal tail (CTT) with an otherwise similar multidomain organization to its SecA(1) homologues and conserved binding of ATP-γ-S. The average in vitro ATPase activity rate of C. difficile SecA2 was 2.6 ± 0.1 µmolPi/min/µmol. Template-based modeling combined with evolutionary conservation analysis supports a model where C. difficile SecA2 in open conformation binds the target protein, ensures its movement through the SecY channel, and enables dimerization through PPXD/HWD cross-interaction of monomers during the process. Both approaches exposed regions with differences between SecA(1) and SecA2 homologues, which are in agreement with the unique adaptation of SecA2 proteins for a specific type of substrate, a role that can be addressed in further studies.
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Affiliation(s)
- Nataša Lindič
- Department of Biochemistry, Molecular and Structural Biology, Jozef Stefan Institute, Jamova Cesta 39, 1000 Ljubljana, Slovenia; (N.L.); (J.L.); (A.U.); (R.V.)
| | - Jure Loboda
- Department of Biochemistry, Molecular and Structural Biology, Jozef Stefan Institute, Jamova Cesta 39, 1000 Ljubljana, Slovenia; (N.L.); (J.L.); (A.U.); (R.V.)
| | - Aleksandra Usenik
- Department of Biochemistry, Molecular and Structural Biology, Jozef Stefan Institute, Jamova Cesta 39, 1000 Ljubljana, Slovenia; (N.L.); (J.L.); (A.U.); (R.V.)
- Centre of Excellence for Integrated Approaches in Chemistry and Biology of Proteins (CIPKeBiP), Jamova Cesta 39, 1000 Ljubljana, Slovenia
| | - Robert Vidmar
- Department of Biochemistry, Molecular and Structural Biology, Jozef Stefan Institute, Jamova Cesta 39, 1000 Ljubljana, Slovenia; (N.L.); (J.L.); (A.U.); (R.V.)
| | - Dušan Turk
- Department of Biochemistry, Molecular and Structural Biology, Jozef Stefan Institute, Jamova Cesta 39, 1000 Ljubljana, Slovenia; (N.L.); (J.L.); (A.U.); (R.V.)
- Centre of Excellence for Integrated Approaches in Chemistry and Biology of Proteins (CIPKeBiP), Jamova Cesta 39, 1000 Ljubljana, Slovenia
- Correspondence: ; Tel.: +386-1-477-3857
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5
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Sanganna Gari RR, Chattrakun K, Marsh BP, Mao C, Chada N, Randall LL, King GM. Direct visualization of the E. coli Sec translocase engaging precursor proteins in lipid bilayers. SCIENCE ADVANCES 2019; 5:eaav9404. [PMID: 31206019 PMCID: PMC6561738 DOI: 10.1126/sciadv.aav9404] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Accepted: 05/09/2019] [Indexed: 06/09/2023]
Abstract
Escherichia coli exports proteins via a translocase comprising SecA and the translocon, SecYEG. Structural changes of active translocases underlie general secretory system function, yet directly visualizing dynamics has been challenging. We imaged active translocases in lipid bilayers as a function of precursor protein species, nucleotide species, and stage of translocation using atomic force microscopy (AFM). Starting from nearly identical initial states, SecA more readily dissociated from SecYEG when engaged with the precursor of outer membrane protein A as compared to the precursor of galactose-binding protein. For the SecA that remained bound to the translocon, the quaternary structure varied with nucleotide, populating SecA2 primarily with adenosine diphosphate (ADP) and adenosine triphosphate, and the SecA monomer with the transition state analog ADP-AlF3. Conformations of translocases exhibited precursor-dependent differences on the AFM imaging time scale. The data, acquired under near-native conditions, suggest that the translocation process varies with precursor species.
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Affiliation(s)
| | - Kanokporn Chattrakun
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
| | - Brendan P. Marsh
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
| | - Chunfeng Mao
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
| | - Nagaraju Chada
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
| | - Linda L. Randall
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
| | - Gavin M. King
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
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6
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Young J, Duong F. Investigating the stability of the SecA-SecYEG complex during protein translocation across the bacterial membrane. J Biol Chem 2019; 294:3577-3587. [PMID: 30602566 DOI: 10.1074/jbc.ra118.006447] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2018] [Revised: 12/21/2018] [Indexed: 11/06/2022] Open
Abstract
During posttranslational translocation in Escherichia coli, polypeptide substrates are driven across the membrane through the SecYEG protein-conducting channel using the ATPase SecA, which binds to SecYEG and couples nucleotide hydrolysis to polypeptide movement. Recent studies suggest that SecA is a highly dynamic enzyme, able to repeatedly bind and dissociate from SecYEG during substrate translocation, but other studies indicate that these dynamics, here referred to as "SecA processivity," are not a requirement for transport. We employ a SecA mutant (PrlD23) that associates more tightly to membranes than WT SecA, in addition to a SecA-SecYEG cross-linked complex, to demonstrate that SecA-SecYEG binding and dissociation events are important for efficient transport of the periplasmic protein proPhoA. Strikingly however, we find that transport of the precursor of the outer membrane protein proOmpA does not depend on SecA processivity. By exchanging signal sequence and protein domains of similar size between PhoA and OmpA, we find that SecA processivity is not influenced by the sequence of the protein substrate. In contrast, using an extended proOmpA variant and a truncated derivative of proPhoA, we show that SecA processivity is affected by substrate length. These findings underscore the importance of the dynamic nature of SecA-SecYEG interactions as a function of the preprotein substrate, features that have not yet been reported using other biophysical or in vivo methods.
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Affiliation(s)
- John Young
- From the Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
| | - Franck Duong
- From the Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
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7
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Crane JM, Randall LL. The Sec System: Protein Export in Escherichia coli. EcoSal Plus 2017; 7:10.1128/ecosalplus.ESP-0002-2017. [PMID: 29165233 PMCID: PMC5807066 DOI: 10.1128/ecosalplus.esp-0002-2017] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Indexed: 11/20/2022]
Abstract
In Escherichia coli, proteins found in the periplasm or the outer membrane are exported from the cytoplasm by the general secretory, Sec, system before they acquire stably folded structure. This dynamic process involves intricate interactions among cytoplasmic and membrane proteins, both peripheral and integral, as well as lipids. In vivo, both ATP hydrolysis and proton motive force are required. Here, we review the Sec system from the inception of the field through early 2016, including biochemical, genetic, and structural data.
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Affiliation(s)
- Jennine M. Crane
- Department of Biochemistry, University of Missouri, Columbia, Missouri
| | - Linda L. Randall
- Department of Biochemistry, University of Missouri, Columbia, Missouri
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8
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Yazdi AK, Vezina GC, Shilton BH. An alternate mode of oligomerization for E. coli SecA. Sci Rep 2017; 7:11747. [PMID: 28924213 PMCID: PMC5603524 DOI: 10.1038/s41598-017-11648-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 08/29/2017] [Indexed: 11/08/2022] Open
Abstract
SecA is the ATPase of preprotein translocase. SecA is a dimer in solution and changes in its oligomeric state may function in preprotein translocation. The SecA-N68 construct, in which the C-terminal helical domains of SecA are deleted, was used to investigate the mechanism of SecA oligomerization. SecA-N68 is in equilibrium between monomers, dimers, and tetramers. Subunit interactions in the SecA-N68 tetramer are mediated entirely by unstructured regions at its N- and C-termini: when the termini are deleted to yield SecA-N68∆NC, the construct is completely monomeric. This monomeric construct yielded crystals diffracting to 2.6 Å that were used to solve the structure of SecA-N68, including the "preprotein crosslinking domain" (PPXD) that was missing from previous E. coli SecA structures. The SecA-N68 structure was combined with small angle X-ray scattering (SAXS) data to construct a model of the SecA-N68 tetramer that is consistent with the essential roles of the extreme N- and C-termini in oligomerization. This mode of oligomerization, which depends on binding of the extreme N-terminus to the DEAD motor domains, NBD1 and NBD2, was used to model a novel parallel and flexible SecA solution dimer that agrees well with SAXS data.
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Affiliation(s)
- Aliakbar Khalili Yazdi
- Department of Biochemistry, University of Western Ontario, London, Ontario, N6A 5C1, Canada
| | - Grant C Vezina
- Department of Biochemistry, University of Western Ontario, London, Ontario, N6A 5C1, Canada
| | - Brian H Shilton
- Department of Biochemistry, University of Western Ontario, London, Ontario, N6A 5C1, Canada.
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9
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Nishiyama KI, Tokuda H. Novel translocation intermediate allows re-evaluation of roles of ATP, proton motive force and SecG at the late stage of preprotein translocation. Genes Cells 2016; 21:1353-1364. [PMID: 27813233 DOI: 10.1111/gtc.12447] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Accepted: 10/05/2016] [Indexed: 11/30/2022]
Abstract
Presecretory proteins such as pOmpA are translocated across the inner membrane of Escherichia coli by Sec translocase powered by ATP and proton motive force (PMF). Translocation activity has been determined by protease protection assaying in vitro. We identified a new translocation intermediate at a late stage, which was protected by proteinase K (PK), but became PK sensitive upon urea extraction. At a late stage of pOmpA translocation driven by PMF in the presence of a nonhydrolyzable ATP analogue, the PK-protected materials arose, but were pulled back upon urea extraction, indicating that completion of translocation requires ATP hydrolysis. When inverted membrane vesicles prepared from secG-null strain (ΔSecG IMV) were used in the absence of PMF, the translocation intermediate was accumulated. When the ATP concentration was low in the absence of PMF, the translocation intermediate was also accumulated. Imposition of PMF in the presence of a low ATP concentration caused recovery of pOmpA translocation and resistance to urea extraction for SecG+ IMV, but not for ΔSecG IMV. Thus, analysis of the late translocation intermediate showed that two of three constituents, physiological concentration of ATP, PMF and SecG, are required for the catalytic cycle of preprotein translocation, that is, completion and subsequent initiation of translocation.
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Affiliation(s)
- Ken-Ichi Nishiyama
- Cryobiofrontier Research Center, Faculty of Agriculture, Iwate University, Morioka, 020-8550, Japan.,Department of Biological Chemistry and Food Science, Faculty of Agriculture, Iwate University, Morioka, 020-8550, Japan
| | - Hajime Tokuda
- Faculty of Nutritional Sciences, The University of Morioka, Takizawa, 020-0694, Japan
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10
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Liu X, Zhang W, Zhao Z, Dai X, Yang Y, Bai Z. Protein secretion in Corynebacterium glutamicum. Crit Rev Biotechnol 2016; 37:541-551. [PMID: 27737570 DOI: 10.1080/07388551.2016.1206059] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Corynebacterium glutamicum, a Gram-positive bacterium, has been widely used for the industrial production of amino acids, such as glutamate and lysine, for decades. Due to several characteristics - its ability to secrete properly folded and functional target proteins into culture broth, its low levels of endogenous extracellular proteins and its lack of detectable extracellular hydrolytic enzyme activity - C. glutamicum is also a very favorable host cell for the secretory production of heterologous proteins, important enzymes, and pharmaceutical proteins. The target proteins are secreted into the culture medium, which has attractive advantages over the manufacturing process for inclusion of body expression - the simplified downstream purification process. The secretory process of proteins is complicated and energy consuming. There are two major secretory pathways in C. glutamicum, the Sec pathway and the Tat pathway, both have specific signal peptides that mediate the secretion of the target proteins. In the present review, we critically discuss recent progress in the secretory production of heterologous proteins and examine in depth the mechanisms of the protein translocation process in C. glutamicum. Some successful case studies of actual applications of this secretory expression host are also evaluated. Finally, the existing issues and solutions in using C. glutamicum as a host of secretory proteins are specifically addressed.
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Affiliation(s)
- Xiuxia Liu
- a National Engineering Laboratory for Cereal Fermentation Technology , Jiangnan University , Wuxi , China.,b The Key Laboratory of Industrial Biotechnology, Ministry of Education , School of Biotechnology, Jiangnan University , Wuxi , China
| | - Wei Zhang
- a National Engineering Laboratory for Cereal Fermentation Technology , Jiangnan University , Wuxi , China.,b The Key Laboratory of Industrial Biotechnology, Ministry of Education , School of Biotechnology, Jiangnan University , Wuxi , China
| | - Zihao Zhao
- a National Engineering Laboratory for Cereal Fermentation Technology , Jiangnan University , Wuxi , China.,b The Key Laboratory of Industrial Biotechnology, Ministry of Education , School of Biotechnology, Jiangnan University , Wuxi , China
| | - Xiaofeng Dai
- a National Engineering Laboratory for Cereal Fermentation Technology , Jiangnan University , Wuxi , China.,b The Key Laboratory of Industrial Biotechnology, Ministry of Education , School of Biotechnology, Jiangnan University , Wuxi , China
| | - Yankun Yang
- a National Engineering Laboratory for Cereal Fermentation Technology , Jiangnan University , Wuxi , China.,b The Key Laboratory of Industrial Biotechnology, Ministry of Education , School of Biotechnology, Jiangnan University , Wuxi , China
| | - Zhonghu Bai
- a National Engineering Laboratory for Cereal Fermentation Technology , Jiangnan University , Wuxi , China.,b The Key Laboratory of Industrial Biotechnology, Ministry of Education , School of Biotechnology, Jiangnan University , Wuxi , China
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11
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Keller RCA. The role and significance of potential lipid-binding regions in the mitochondrial protein import motor: an in-depth in silico study. 3 Biotech 2015; 5:1041-1051. [PMID: 28324412 PMCID: PMC4624131 DOI: 10.1007/s13205-015-0310-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2015] [Accepted: 05/12/2015] [Indexed: 12/05/2022] Open
Abstract
Over the last two decades, an impressive progress has been made in the identification of novel factors in the translocation machineries of the mitochondrial protein import and their possible roles. The role of lipids and possible protein–lipids interactions remains a relatively unexplored territory. Investigating the role of potential lipid-binding regions in the sub-units of the mitochondrial motor might help to shed some more light in our understanding of protein–lipid interactions mechanistically. Bioinformatics results seem to indicate multiple potential lipid-binding regions in each of the sub-units. The subsequent characterization of some of those regions in silico provides insight into the mechanistic functioning of this intriguing and essential part of the protein translocation machinery. Details about the way the regions interact with phospholipids were found by the use of Monte Carlo simulations. For example, Pam18 contains one possible transmembrane region and two tilted surface bound conformations upon interaction with phospholipids. The results demonstrate that the presented bioinformatics approach might be useful in an attempt to expand the knowledge of the possible role of protein–lipid interactions in the mitochondrial protein translocation process.
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Affiliation(s)
- Rob C A Keller
- Section Chemistry, Charlemagne College, Wilhelminastraat 13-15, 6524 AJ, Nijmegen, The Netherlands.
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12
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Denks K, Vogt A, Sachelaru I, Petriman NA, Kudva R, Koch HG. The Sec translocon mediated protein transport in prokaryotes and eukaryotes. Mol Membr Biol 2014; 31:58-84. [DOI: 10.3109/09687688.2014.907455] [Citation(s) in RCA: 123] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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13
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Singh R, Kraft C, Jaiswal R, Sejwal K, Kasaragod VB, Kuper J, Bürger J, Mielke T, Luirink J, Bhushan S. Cryo-electron microscopic structure of SecA protein bound to the 70S ribosome. J Biol Chem 2014; 289:7190-7199. [PMID: 24443566 DOI: 10.1074/jbc.m113.506634] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
SecA is an ATP-dependent molecular motor pumping secretory and outer membrane proteins across the cytoplasmic membrane in bacteria. SecA associates with the protein-conducting channel, the heterotrimeric SecYEG complex, in a so-called posttranslational manner. A recent study further showed binding of a monomeric state of SecA to the ribosome. However, the true oligomeric state of SecA remains controversial because SecA can also form functional dimers, and high-resolution crystal structures exist for both the monomer and the dimer. Here we present the cryo-electron microscopy structures of Escherichia coli SecA bound to the ribosome. We show that not only a monomeric SecA binds to the ribosome but also that two copies of SecA can be observed that form an elongated dimer. Two copies of SecA completely surround the tunnel exit, providing a unique environment to the nascent polypeptides emerging from the ribosome. We identified the N-terminal helix of SecA required for a stable association with the ribosome. The structures indicate a possible function of the dimeric form of SecA at the ribosome.
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Affiliation(s)
- Rajkumar Singh
- Rudolf Virchow Center/DFG Research Center for Experimental Biomedicine, University of Würzburg, Josef Schneider Str. 2, 97078 Würzburg, Germany
| | - Christian Kraft
- Rudolf Virchow Center/DFG Research Center for Experimental Biomedicine, University of Würzburg, Josef Schneider Str. 2, 97078 Würzburg, Germany
| | - Rahul Jaiswal
- Division of Structural Biology and Biochemistry, School of Biological Sciences, Nanyang Technological University, Singapore 637551
| | - Kushal Sejwal
- Rudolf Virchow Center/DFG Research Center for Experimental Biomedicine, University of Würzburg, Josef Schneider Str. 2, 97078 Würzburg, Germany
| | - Vikram Babu Kasaragod
- Rudolf Virchow Center/DFG Research Center for Experimental Biomedicine, University of Würzburg, Josef Schneider Str. 2, 97078 Würzburg, Germany
| | - Jochen Kuper
- Rudolf Virchow Center/DFG Research Center for Experimental Biomedicine, University of Würzburg, Josef Schneider Str. 2, 97078 Würzburg, Germany
| | - Jörg Bürger
- UltraStrukturNetzwerk, Max Planck Institute for Molecular Genetics, Ihnestr. 73, 14195 Berlin, Germany; Institut für Medizinische Physik und Biophysik, Charité, Ziegelstrasse 5-8, 10117 Berlin, Germany
| | - Thorsten Mielke
- UltraStrukturNetzwerk, Max Planck Institute for Molecular Genetics, Ihnestr. 73, 14195 Berlin, Germany; Institut für Medizinische Physik und Biophysik, Charité, Ziegelstrasse 5-8, 10117 Berlin, Germany
| | - Joen Luirink
- Department of Molecular Microbiology, Institute of Molecular Cell Biology, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands
| | - Shashi Bhushan
- Rudolf Virchow Center/DFG Research Center for Experimental Biomedicine, University of Würzburg, Josef Schneider Str. 2, 97078 Würzburg, Germany; Division of Structural Biology and Biochemistry, School of Biological Sciences, Nanyang Technological University, Singapore 637551.
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14
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Stoichiometry of SecYEG in the active translocase of Escherichia coli varies with precursor species. Proc Natl Acad Sci U S A 2013; 110:11815-20. [PMID: 23818593 DOI: 10.1073/pnas.1303289110] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have established a reconstitution system for the translocon SecYEG in proteoliposomes in which 55% of the accessible translocons are active. This level corresponds to the fraction of translocons that are active in vitro when assessed in their native environment of cytoplasmic membrane vesicles. Assays using these robust reconstituted proteoliposomes and cytoplasmic membrane vesicles have revealed that the number of SecYEG units involved in an active translocase depends on the precursor undergoing transfer. The active translocase for the precursor of periplasmic galactose-binding protein contains twice the number of heterotrimeric units of SecYEG as does that for the precursor of outer membrane protein A.
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15
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Kudva R, Denks K, Kuhn P, Vogt A, Müller M, Koch HG. Protein translocation across the inner membrane of Gram-negative bacteria: the Sec and Tat dependent protein transport pathways. Res Microbiol 2013; 164:505-34. [DOI: 10.1016/j.resmic.2013.03.016] [Citation(s) in RCA: 122] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Accepted: 03/11/2013] [Indexed: 11/28/2022]
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16
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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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Prediction of Lipid-Binding Regions in Cytoplasmic and Extracellular Loops of Membrane Proteins as Exemplified by Protein Translocation Membrane Proteins. J Membr Biol 2012; 246:21-9. [DOI: 10.1007/s00232-012-9498-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2012] [Accepted: 08/18/2012] [Indexed: 02/07/2023]
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