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The conformations and basal conformational dynamics of translocation factor SecDF vary with translocon SecYEG interaction. J Biol Chem 2022; 298:102412. [PMID: 36007614 PMCID: PMC9508474 DOI: 10.1016/j.jbc.2022.102412] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Revised: 08/10/2022] [Accepted: 08/15/2022] [Indexed: 11/22/2022] Open
Abstract
The general secretory, or Sec, system is a primary protein export pathway from the cytosol of Escherichia coli and all eubacteria. Integral membrane protein complex SecDF is a translocation factor that enhances polypeptide secretion, which is driven by the Sec translocase, consisting of translocon SecYEG and ATPase SecA. SecDF is thought to utilize a proton gradient to effectively pull precursor proteins from the cytoplasm into the periplasm. Working models have been developed to describe the structure and function of SecDF, but important mechanistic questions remain unanswered. Atomic force microscopy (AFM) is a powerful technique for studying the dynamics of single-molecule systems including membrane proteins in near-native conditions. The sharp tip of the AFM provides direct access to membrane-external protein conformations. Here, we acquired AFM images and kymographs (∼100 ms resolution) to visualize SecDF protrusions in near-native supported lipid bilayers and compared the experimental data to simulated AFM images based on static structures. When studied in isolation, SecDF exhibited a stable and compact conformation close to the lipid bilayer surface, indicative of a resting state. Interestingly, upon SecYEG introduction, we observed changes in both SecDF conformation and conformational dynamics. The population of periplasmic protrusions corresponding to an intermediate form of SecDF, which is thought to be active in precursor protein handling, increased >9-fold. In conjunction, our dynamics measurements revealed an enhancement in the transition rate between distinct SecDF conformations when the translocon was present. Together, this work provides a novel vista of basal-level SecDF conformational dynamics in near-native conditions.
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Komarudin AG, Driessen AJM. SecA-Mediated Protein Translocation through the SecYEG Channel. Microbiol Spectr 2019; 7:10.1128/microbiolspec.psib-0028-2019. [PMID: 31373268 PMCID: PMC10957188 DOI: 10.1128/microbiolspec.psib-0028-2019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2019] [Indexed: 01/02/2023] Open
Abstract
In bacteria, the Sec translocase mediates the translocation of proteins into and across the cytoplasmic membrane. It consists of a protein conducting channel SecYEG, the ATP-dependent motor SecA, and the accessory SecDF complex. Here we discuss the function and structure of the Sec translocase.
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Affiliation(s)
- Amalina Ghaisani Komarudin
- Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, and the Zernike Institute of Advanced Materials, University of Groningen, Nijenborgh 7, 9747AG Groningen, The Netherlands
| | - Arnold J M Driessen
- Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, and the Zernike Institute of Advanced Materials, University of Groningen, Nijenborgh 7, 9747AG Groningen, The Netherlands
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Fu X, Chang Z. Biogenesis, quality control, and structural dynamics of proteins as explored in living cells via site-directed photocrosslinking. Protein Sci 2019; 28:1194-1209. [PMID: 31002747 DOI: 10.1002/pro.3627] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2019] [Accepted: 04/16/2019] [Indexed: 02/06/2023]
Abstract
Protein biogenesis and quality control are essential to maintaining a functional pool of proteins and involve numerous protein factors that dynamically and transiently interact with each other and with the substrate proteins in living cells. Conventional methods are hardly effective for studying dynamic, transient, and weak protein-protein interactions that occur in cells. Herein, we review how the site-directed photocrosslinking approach, which relies on the genetic incorporation of a photoreactive unnatural amino acid into a protein of interest at selected individual amino acid residue positions and the covalent trapping of the interacting proteins upon ultraviolent irradiation, has become a highly efficient way to explore the aspects of protein contacts in living cells. For example, in the past decade, this approach has allowed the profiling of the in vivo substrate proteins of chaperones or proteases under both physiologically optimal and stressful (e.g., acidic) conditions, mapping residues located at protein interfaces, identifying new protein factors involved in the biogenesis of membrane proteins, trapping transiently formed protein complexes, and snapshotting different structural states of a protein. We anticipate that the site-directed photocrosslinking approach will play a fundamental role in dissecting the detailed mechanisms of protein biogenesis, quality control, and dynamics in the future.
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Affiliation(s)
- Xinmiao Fu
- Provincial University Key Laboratory of Cellular Stress Response and Metabolic Regulation, Key Laboratory of OptoElectronic Science and Technology for Medicine of Ministry of Education, College of Life Sciences, Fujian Normal University, Fuzhou City, Fujian Province, 350117, China
| | - Zengyi Chang
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Center for Protein Science, Beijing, 100871, China
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Miyazaki R, Akiyama Y, Mori H. A photo-cross-linking approach to monitor protein dynamics in living cells. Biochim Biophys Acta Gen Subj 2019; 1864:129317. [PMID: 30851405 DOI: 10.1016/j.bbagen.2019.03.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 02/26/2019] [Accepted: 03/04/2019] [Indexed: 11/16/2022]
Abstract
BACKGROUND Proteins, which comprise one of the major classes of biomolecules that constitute a cell, interact with other cellular factors during both their biogenesis and functional states. Studying not only static but also transient interactions of proteins is important to understand their physiological roles and regulation mechanisms. However, only a limited number of methods are available to analyze the dynamic behaviors of proteins at the molecular level in a living cell. The site-directed in vivo photo-cross-linking approach is an elegant technique to capture protein interactions with high spatial resolution in a living cell. SCOPE OF REVIEW Here, we review the in vivo photo-cross-linking approach including its recent applications and the potential problems to be considered. We also introduce a new in vivo photo-cross-linking-based technique (PiXie) to study protein dynamics with high spatiotemporal resolution. MAJOR CONCLUSIONS In vivo photo-cross-linking enables us to capture weak/transient protein interactions with high spatial resolution, and allows for identification of interacting factors. Moreover, the PiXie approach can be used to monitor rapid folding/assembly processes of proteins in living cells. GENERAL SIGNIFICANCE In vivo photo-cross-linking is a simple method that has been used to analyze the dynamic interactions of many cellular proteins. Originally developed in Escherichia coli, this system has been extended to studies in various organisms, making it a fundamental technique for investigating dynamic protein interactions in many cellular processes. This article is part of a Special issue entitled "Novel major techniques for visualizing 'live' protein molecules" edited by Dr. Daisuke Kohda.
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Affiliation(s)
- Ryoji Miyazaki
- Institute for Frontier Life and Medical Sciences, Kyoto University, Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan
| | - Yoshinori Akiyama
- Institute for Frontier Life and Medical Sciences, Kyoto University, Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan
| | - Hiroyuki Mori
- Institute for Frontier Life and Medical Sciences, Kyoto University, Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan.
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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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Banerjee T, Zheng Z, Abolafia J, Harper S, Oliver D. The SecA protein deeply penetrates into the SecYEG channel during insertion, contacting most channel transmembrane helices and periplasmic regions. J Biol Chem 2017; 292:19693-19707. [PMID: 28986446 DOI: 10.1074/jbc.ra117.000130] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Indexed: 11/06/2022] Open
Abstract
The bacterial Sec-dependent system is the major protein-biogenic pathway for protein secretion across the cytoplasmic membrane or insertion of integral membrane proteins into the phospholipid bilayer. The mechanism of SecA-driven protein transport across the SecYEG channel complex has remained controversial with conflicting claims from biochemical and structural studies regarding the depth and extent of SecA insertion into SecYEG during ongoing protein transport. Here we utilized site-specific in vivo photo-crosslinking to thoroughly map SecY regions that are in contact with SecA during its insertion cycle. An arabinose-inducible, rapidly folding OmpA-GFP chimera was utilized to jam the SecYEG channels with an arrested substrate protein to "freeze" them in their SecA-inserted state. Examination of 117 sites distributed throughout SecY indicated that SecA not only interacts extensively with the cytosolic regions of SecY as shown previously, but it also interacts with most of the transmembrane helices and periplasmic regions of SecY, with a clustering of interaction sights around the lateral gate and pore ring regions. Our observations support previous reports of SecA membrane insertion during in vitro protein transport as well as those documenting the membrane penetration properties of this protein. They suggest that one or more SecA regions transiently integrate into the heart of the SecY channel complex to span the membrane to promote the protein transport cycle. These findings indicate that high-resolution structural information about the membrane-inserted state of SecA is still lacking and will be critical for elucidating the bacterial protein transport mechanism.
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Affiliation(s)
- Tithi Banerjee
- From the Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459
| | - Zeliang Zheng
- From the Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459
| | - Jane Abolafia
- From the Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459
| | - Shelby Harper
- From the Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459
| | - Donald Oliver
- From the Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459
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Sugano Y, Furukawa A, Nureki O, Tanaka Y, Tsukazaki T. SecY-SecA fusion protein retains the ability to mediate protein transport. PLoS One 2017; 12:e0183434. [PMID: 28820900 PMCID: PMC5562318 DOI: 10.1371/journal.pone.0183434] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 07/28/2017] [Indexed: 01/05/2023] Open
Abstract
In bacteria, the membrane protein complex SecY/E/G and SecA ATPase are essential for protein translocation. About 30% of newly synthesized proteins in the cytosol are targeted to and translocated across the cytoplasmic membrane by the Sec factors. Although a number of single-molecule analyses and structural studies, including the crystal structure of SecYEG complexed with SecA, have been published, the underlying molecular mechanisms and the functional oligomer states remain elusive. In this study, we constructed a fusion protein SecY-SecA, which induces the formation of the SecY-A/SecE/SecG complex (SecYAEG), to enable investigation of the molecular mechanisms by advanced single-molecule analyses. SecYAEG-reconstituted liposomes were found to possess protein translocation activity in vitro and form stable intermediates capable of the translocation using a mutant substrate protein. We additionally found that one unit of SecYAEG complex embedded into a nanodisc, using membrane scaffold proteins, interacts strongly with the substrate. The isolated SecYAEG-reconstituted nanodisc is a promising tool for investigation of the molecular mechanisms by which a single unit of Sec machinery mediates protein translocation.
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Affiliation(s)
- Yasunori Sugano
- Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, Japan
| | - Arata Furukawa
- Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, Japan
| | - Osamu Nureki
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan
| | - Yoshiki Tanaka
- Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, Japan
| | - Tomoya Tsukazaki
- Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, Japan
- * E-mail:
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Banerjee T, Lindenthal C, Oliver D. SecA functions in vivo as a discrete anti-parallel dimer to promote protein transport. Mol Microbiol 2016; 103:439-451. [PMID: 27802584 DOI: 10.1111/mmi.13567] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/26/2016] [Indexed: 01/28/2023]
Abstract
SecA ATPase motor protein plays a central role in bacterial protein transport by binding substrate proteins and the SecY channel complex and utilizing its ATPase activity to drive protein translocation across the plasma membrane. SecA has been shown to exist in a dynamic monomer-dimer equilibrium modulated by translocation ligands, and multiple structural forms of the dimer have been crystallized. Since the structural form of the dimer remains a controversial and unresolved question, we addressed this matter by engineering ρ-benzoylphenylalanine along dimer interfaces corresponding to the five different SecA X-ray structures and assessing their in vivo photo-crosslinking pattern. A discrete anti-parallel 1M6N-like dimer was the dominant if not exclusive dimer found in vivo, whether SecA was cytosolic or in lipid or SecYEG-bound states. SecA bound to a stable translocation intermediate was crosslinked in vivo to a second SecA protomer at its 1M6N interface, suggesting that this specific dimer likely promotes active protein translocation. Taken together, our studies strengthen models that posit, at least in part, a SecA dimer-driven translocation mechanism.
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Affiliation(s)
- Tithi Banerjee
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, CT, 06459, USA
| | - Christine Lindenthal
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, CT, 06459, USA
| | - Donald Oliver
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, CT, 06459, USA
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