1
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Sun C, Slade L, Mbonu P, Ordner H, Mitchell C, Mitchell M, Liang FC. Membrane protein chaperone and sodium chloride modulate the kinetics and morphology of amyloid beta aggregation. FEBS J 2024; 291:158-176. [PMID: 37786925 DOI: 10.1111/febs.16967] [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: 12/13/2022] [Revised: 07/04/2023] [Accepted: 09/29/2023] [Indexed: 10/04/2023]
Abstract
Protein aggregation is a biological phenomenon caused by the accumulation of misfolded proteins. Amyloid beta (Aβ) peptides are derived from the cleavage of a larger membrane protein molecule and accumulate to form plaques extracellularly. According to the amyloid hypothesis, accumulation of Aβ aggregates in the brain is primarily responsible for the pathogenesis of Alzheimer's disease (AD). Therefore, the disassembly of Aβ aggregates may provide opportunities for alleviating or treating AD. Here, we show that the novel protein targeting machinery from chloroplast, chloroplast signal recognition particle 43 (cpSRP43), is an ATP-independent membrane protein chaperone that can both prevent and reverse Aβ aggregation effectively. Using of thioflavin T dye, we obtained the aggregation kinetics of Aβ aggregation and determined that the chaperone prevents Aβ aggregation in a concentration-dependent manner. Size exclusion chromatography and sedimentation assays showed that 10-fold excess of cpSRP43 can keep Aβ in the soluble monomeric form. Electron microscopy showed that the fibril structure was disrupted in the presence of this chaperone. Importantly, cpSRP43 utilizes the binding energy to actively remodel the preformed Aβ aggregates without assistance by a co-chaperone and ATP, emphasizing its unique function among protein chaperones. Moreover, when sodium chloride concentration is higher than 25 mm, the Aβ aggregation rate increases drastically to form tightly associated aggregates and generate more oligomers. Our results demonstrate that the presence of cpSRP43 and low NaCl levels inhibit or retard Aβ peptide aggregation, potentially opening new avenues to strategically develop an effective treatment for AD.
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Affiliation(s)
- Christopher Sun
- Department of Biology, Midwestern State University, Wichita Falls, TX, USA
| | - Leah Slade
- Department of Chemistry, Midwestern State University, Wichita Falls, TX, USA
| | - Prisca Mbonu
- Department of Biology, Midwestern State University, Wichita Falls, TX, USA
| | - Hunter Ordner
- Department of Chemistry, Midwestern State University, Wichita Falls, TX, USA
| | - Connor Mitchell
- Department of Chemistry, Midwestern State University, Wichita Falls, TX, USA
| | - Matthew Mitchell
- Department of Chemistry, Midwestern State University, Wichita Falls, TX, USA
| | - Fu-Cheng Liang
- Department of Chemistry, Midwestern State University, Wichita Falls, TX, USA
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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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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.
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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
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4
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Ma C, Wu X, Sun D, Park E, Catipovic MA, Rapoport TA, Gao N, Li L. Structure of the substrate-engaged SecA-SecY protein translocation machine. Nat Commun 2019; 10:2872. [PMID: 31253804 PMCID: PMC6599042 DOI: 10.1038/s41467-019-10918-2] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 06/10/2019] [Indexed: 11/28/2022] Open
Abstract
The Sec61/SecY channel allows the translocation of many proteins across the eukaryotic endoplasmic reticulum membrane or the prokaryotic plasma membrane. In bacteria, most secretory proteins are transported post-translationally through the SecY channel by the SecA ATPase. How a polypeptide is moved through the SecA-SecY complex is poorly understood, as structural information is lacking. Here, we report an electron cryo-microscopy (cryo-EM) structure of a translocating SecA-SecY complex in a lipid environment. The translocating polypeptide chain can be traced through both SecA and SecY. In the captured transition state of ATP hydrolysis, SecA’s two-helix finger is close to the polypeptide, while SecA’s clamp interacts with the polypeptide in a sequence-independent manner by inducing a short β-strand. Taking into account previous biochemical and biophysical data, our structure is consistent with a model in which the two-helix finger and clamp cooperate during the ATPase cycle to move a polypeptide through the channel. Proteins are translocated across membranes through the Sec61/SecY channel. Here, the authors present the structure of a translocating peptide chain trapped inside the SecA-SecY complex which suggests how peptides are actively moved through the channel.
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Affiliation(s)
- Chengying Ma
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China
| | - Xiaofei Wu
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China
| | - Dongjie Sun
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China
| | - Eunyong Park
- University of California-Berkeley, Stanley Hall, Berkeley, CA, 94720, USA
| | - Marco A Catipovic
- Department of Cell Biology, Howard Hughes Medical Institute and Harvard Medical School, 240 Longwood Avenue, Boston, MA, 02115, USA
| | - Tom A Rapoport
- Department of Cell Biology, Howard Hughes Medical Institute and Harvard Medical School, 240 Longwood Avenue, Boston, MA, 02115, USA.
| | - Ning Gao
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China.
| | - Long Li
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China.
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5
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Olivares-Quiroz L, Vélez-Pérez JA. Translocation of non-interacting heteropolymer protein chains in terms of single helical propensity and size. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2019; 1867:565-574. [PMID: 30885619 DOI: 10.1016/j.bbapap.2019.03.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Revised: 02/27/2019] [Accepted: 03/13/2019] [Indexed: 11/29/2022]
Abstract
In this work we present an analytical framework to calculate the average translocation time τ required for an ideal proteinogenic polypeptide chain to cross over a small pore on a membrane. Translocation is considered to proceed as a chain of non-interacting amino acid residues of sequence {Xj} diffuses through the pore against an energy barrier Δℱ, set by chain entropy and unfolding-folding energetics. We analyze the effect of sequence heterogeneity on the dynamics of translocation by means of helical propensity of amino acid residues. In our calculations we use sequences of fifteen well-known proteins that are translocated which span two orders of magnitude in size according to the number of residues N. Results show non-symmetric free energy barriers as a consequence of sequence heterogeneity, such asymmetry in energy may be useful in differentiated directions of translocation. For the fifteen polypeptide chains considered we found conditions when sequence heterogeneity has not a significant effect on the time scale of translocation leading to a scaling law τ ∝ Nν, where ν ∼ 1.6 is an exponent that holds for most ground state energies. We also identify conditions when sequence heterogeneity has a great impact on the time scale of translocation, in consequence, no more scaling laws for τ there exist.
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Affiliation(s)
- L Olivares-Quiroz
- Departamento de Fisica and Posgrado en Ciencias de la Complejidad, Universidad Autonoma de la Ciudad de Mexico, CP 09760 Mexico City, Mexico; Centro de Ciencias de la Complejidad C3, UNAM, Circuito Mario de la Cueva 20, CP 04510 Mexico City, Mexico.
| | - José Antonio Vélez-Pérez
- Depto. Matemáticas y Mecánica, I.I.M.A.S., Universidad Nacional Autónoma de México, Apdo. Postal 20-726, 01000 Cd. México, Mexico; Posgrado en Nanociencias y Nanotecnología, Centro de Investigación y de Estudios Avanzados del IPN, Ap. Postal: 14-740, 07000 México, DF, Mexico.
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6
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Knyazev DG, Kuttner R, Zimmermann M, Sobakinskaya E, Pohl P. Driving Forces of Translocation Through Bacterial Translocon SecYEG. J Membr Biol 2018; 251:329-343. [PMID: 29330604 PMCID: PMC6028853 DOI: 10.1007/s00232-017-0012-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2017] [Accepted: 12/22/2017] [Indexed: 11/09/2022]
Abstract
This review focusses on the energetics of protein translocation via the Sec translocation machinery. First we complement structural data about SecYEG's conformational rearrangements by insight obtained from functional assays. These include measurements of SecYEG permeability that allow assessment of channel gating by ligand binding and membrane voltage. Second we will discuss the power stroke and Brownian ratcheting models of substrate translocation and the role that the two models assign to the putative driving forces: (i) ATP (SecA) and GTP (ribosome) hydrolysis, (ii) interaction with accessory proteins, (iii) membrane partitioning and folding, (iv) proton motive force (PMF), and (v) entropic contributions. Our analysis underlines how important energized membranes are for unravelling the translocation mechanism in future experiments.
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Affiliation(s)
- Denis G Knyazev
- Johannes Kepler University Linz, Institute of Biophysics, Linz, Austria.
| | - Roland Kuttner
- Johannes Kepler University Linz, Institute of Biophysics, Linz, Austria
| | - Mirjam Zimmermann
- Johannes Kepler University Linz, Institute of Biophysics, Linz, Austria
| | | | - Peter Pohl
- Johannes Kepler University Linz, Institute of Biophysics, Linz, Austria
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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: 57] [Impact Index Per Article: 8.1] [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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Gonsberg A, Jung S, Ulbrich S, Origi A, Ziska A, Baier M, Koch HG, Zimmermann R, Winklhofer KF, Tatzelt J. The Sec61/SecY complex is inherently deficient in translocating intrinsically disordered proteins. J Biol Chem 2017; 292:21383-21396. [PMID: 29084847 DOI: 10.1074/jbc.m117.788067] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2017] [Revised: 10/26/2017] [Indexed: 11/06/2022] Open
Abstract
About one-quarter to nearly one-third of the proteins synthesized in the cytosol of eukaryotic cells are integrated into the plasma membrane or are secreted. Translocation of secretory proteins into the lumen of the endoplasmic reticulum or the periplasm of bacteria is mediated by a highly conserved heterotrimeric membrane protein complex denoted Sec61 in eukaryotes and SecYEG in bacteria. To evaluate a possible modulation of the translocation efficiency by secondary structures of the nascent peptide chain, we performed a comparative analysis in bacteria, yeast, and mammalian cells. Strikingly, neither the bacterial SecY nor the eukaryotic Sec61 translocon was able to efficiently transport proteins entirely composed of intrinsically disordered domains (IDDs) or β-strands. However, translocation could be restored by α-helical domains in a position- and organism-dependent manner. In bacteria, we found that the α-helical domains have to precede the IDD or β-strands, whereas in mammalian cells, C-terminally located α-helical domains are sufficient to promote translocation. Our study reveals an evolutionarily conserved deficiency of the Sec61/SecY complex to translocate IDDs and β-strands in the absence of α-helical domains. Moreover, our results may suggest that adaptive pathways co-evolved with the expansion of IDDs in the proteome of eukaryotic cells to increase the transport capacity of the Sec61 translocon.
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Affiliation(s)
- Anika Gonsberg
- From the Departments of Biochemistry of Neurodegenerative Diseases and
| | - Sebastian Jung
- From the Departments of Biochemistry of Neurodegenerative Diseases and
| | - Sarah Ulbrich
- From the Departments of Biochemistry of Neurodegenerative Diseases and
| | - Andrea Origi
- the Institute of Biochemistry and Molecular Biology, Faculty of Medicine, Albert-Ludwigs-University Freiburg, D-79104 Freiburg im Breisgau, Germany
| | - Anke Ziska
- the Department of Medical Biochemistry and Molecular Biology, Saarland University, D-66421 Homburg, Germany, and
| | - Michael Baier
- the Research Group Proteinopathies/Neurodegenerative Diseases, Centre for Biological Threats and Special Pathogens, Robert Koch-Institut, D-13353 Berlin, Germany
| | - Hans-Georg Koch
- the Institute of Biochemistry and Molecular Biology, Faculty of Medicine, Albert-Ludwigs-University Freiburg, D-79104 Freiburg im Breisgau, Germany
| | - Richard Zimmermann
- the Department of Medical Biochemistry and Molecular Biology, Saarland University, D-66421 Homburg, Germany, and
| | - Konstanze F Winklhofer
- Molecular Cell Biology, Institute of Biochemistry and Pathobiochemistry, Ruhr University Bochum, D-44801 Bochum, Germany
| | - Jörg Tatzelt
- From the Departments of Biochemistry of Neurodegenerative Diseases and
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9
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Collinson I, Corey RA, Allen WJ. Channel crossing: how are proteins shipped across the bacterial plasma membrane? Philos Trans R Soc Lond B Biol Sci 2016; 370:rstb.2015.0025. [PMID: 26370937 PMCID: PMC4632601 DOI: 10.1098/rstb.2015.0025] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The structure of the first protein-conducting channel was determined more than a decade ago. Today, we are still puzzled by the outstanding problem of protein translocation—the dynamic mechanism underlying the consignment of proteins across and into membranes. This review is an attempt to summarize and understand the energy transducing capabilities of protein-translocating machines, with emphasis on bacterial systems: how polypeptides make headway against the lipid bilayer and how the process is coupled to the free energy associated with ATP hydrolysis and the transmembrane protein motive force. In order to explore how cargo is driven across the membrane, the known structures of the protein-translocation machines are set out against the background of the historic literature, and in the light of experiments conducted in their wake. The paper will focus on the bacterial general secretory (Sec) pathway (SecY-complex), and its eukaryotic counterpart (Sec61-complex), which ferry proteins across the membrane in an unfolded state, as well as the unrelated Tat system that assembles bespoke channels for the export of folded proteins.
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Affiliation(s)
- Ian Collinson
- School of Biochemistry, University of Bristol, University Walk, Bristol BS8 1TD, UK
| | - Robin A Corey
- School of Biochemistry, University of Bristol, University Walk, Bristol BS8 1TD, UK
| | - William J Allen
- School of Biochemistry, University of Bristol, University Walk, Bristol BS8 1TD, UK
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10
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Allen WJ, Corey RA, Oatley P, Sessions RB, Baldwin SA, Radford SE, Tuma R, Collinson I. Two-way communication between SecY and SecA suggests a Brownian ratchet mechanism for protein translocation. eLife 2016; 5. [PMID: 27183269 PMCID: PMC4907695 DOI: 10.7554/elife.15598] [Citation(s) in RCA: 74] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 05/14/2016] [Indexed: 01/25/2023] Open
Abstract
The essential process of protein secretion is achieved by the ubiquitous Sec machinery. In prokaryotes, the drive for translocation comes from ATP hydrolysis by the cytosolic motor-protein SecA, in concert with the proton motive force (PMF). However, the mechanism through which ATP hydrolysis by SecA is coupled to directional movement through SecYEG is unclear. Here, we combine all-atom molecular dynamics (MD) simulations with single molecule FRET and biochemical assays. We show that ATP binding by SecA causes opening of the SecY-channel at long range, while substrates at the SecY-channel entrance feed back to regulate nucleotide exchange by SecA. This two-way communication suggests a new, unifying 'Brownian ratchet' mechanism, whereby ATP binding and hydrolysis bias the direction of polypeptide diffusion. The model represents a solution to the problem of transporting inherently variable substrates such as polypeptides, and may underlie mechanisms of other motors that translocate proteins and nucleic acids.
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Affiliation(s)
| | - Robin Adam Corey
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| | - Peter Oatley
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.,School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom
| | | | - Steve A Baldwin
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.,School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom
| | - Sheena E Radford
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.,School of Molecular and Cellular Biology, University of Leeds, Leeds, United Kingdom
| | - Roman Tuma
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.,School of Molecular and Cellular Biology, University of Leeds, Leeds, United Kingdom
| | - Ian Collinson
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
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11
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Kim SK, Park YC, Lee HH, Jeon ST, Min WK, Seo JH. Simple amino acid tags improve both expression and secretion ofCandida antarcticalipase B in recombinantEscherichia coli. Biotechnol Bioeng 2014; 112:346-55. [DOI: 10.1002/bit.25361] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Revised: 08/07/2014] [Accepted: 08/08/2014] [Indexed: 11/12/2022]
Affiliation(s)
- Sun-Ki Kim
- Department of Agricultural Biotechnology and Center for Food and Bioconvergence; Seoul National University; Seoul 151-921 Republic of Korea
| | - Yong-Cheol Park
- Department of Bio and Fermentation Convergence Technology; Kookmin University; Seoul Korea
| | - Hyung Ho Lee
- Department of Bio and Nano Chemistry; Kookmin University; Seoul Korea
| | - Seung Taeg Jeon
- Department of Bio and Nano Chemistry; Kookmin University; Seoul Korea
| | - Won-Ki Min
- Department of Agricultural Biotechnology and Center for Food and Bioconvergence; Seoul National University; Seoul 151-921 Republic of Korea
| | - Jin-Ho Seo
- Department of Agricultural Biotechnology and Center for Food and Bioconvergence; Seoul National University; Seoul 151-921 Republic of Korea
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12
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Zhang B, Miller TF. Direct simulation of early-stage Sec-facilitated protein translocation. J Am Chem Soc 2012; 134:13700-7. [PMID: 22852862 DOI: 10.1021/ja3034526] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Direct simulations reveal key mechanistic features of early-stage protein translocation and membrane integration via the Sec-translocon channel. We present a novel computational protocol that combines non-equilibrium growth of the nascent protein with microsecond timescale molecular dynamics trajectories. Analysis of multiple, long timescale simulations elucidates molecular features of protein insertion into the translocon, including signal-peptide docking at the translocon lateral gate (LG), large lengthscale conformational rearrangement of the translocon LG helices, and partial membrane integration of hydrophobic nascent-protein sequences. Furthermore, the simulations demonstrate the role of specific molecular interactions in the regulation of protein secretion, membrane integration, and integral membrane protein topology. Salt-bridge contacts between the nascent-protein N-terminus, cytosolic translocon residues, and phospholipid head groups are shown to favor conformations of the nascent protein upon early-stage insertion that are consistent with the Type II (N(cyt)/C(exo)) integral membrane protein topology, and extended hydrophobic contacts between the nascent protein and the membrane lipid bilayer are shown to stabilize configurations that are consistent with the Type III (N(exo)/C(cyt)) topology. These results provide a detailed, mechanistic basis for understanding experimentally observed correlations between integral membrane protein topology, translocon mutagenesis, and nascent-protein sequence.
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Affiliation(s)
- Bin Zhang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA
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