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Gassner C, Vongsvivut J, Ng SH, Ryu M, Tobin MJ, Juodkazis S, Morikawa J, Wood BR. Linearly Polarized Infrared Spectroscopy for the Analysis of Biological Materials. APPLIED SPECTROSCOPY 2023; 77:977-1008. [PMID: 37464791 DOI: 10.1177/00037028231180233] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/20/2023]
Abstract
The analysis of biological samples with polarized infrared spectroscopy (p-IR) has long been a widely practiced method for the determination of sample orientation and structural properties. In contrast to earlier works, which employed this method to investigate the fundamental chemistry of biological systems, recent interests are moving toward "real-world" applications for the evaluation and diagnosis of pathological states. This focal point review provides an up-to-date synopsis of the knowledge of biological materials garnered through linearly p-IR on biomolecules, cells, and tissues. An overview of the theory with special consideration to biological samples is provided. Different modalities which can be employed along with their capabilities and limitations are outlined. Furthermore, an in-depth discussion of factors regarding sample preparation, sample properties, and instrumentation, which can affect p-IR analysis is provided. Additionally, attention is drawn to the potential impacts of analysis of biological samples with inherently polarized light sources, such as synchrotron light and quantum cascade lasers. The vast applications of p-IR for the determination of the structure and orientation of biological samples are given. In conclusion, with considerations to emerging instrumentation, findings by other techniques, and the shift of focus toward clinical applications, we speculate on the future directions of this methodology.
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Affiliation(s)
- Callum Gassner
- Centre for Biospectroscopy, School of Chemistry, Monash University, Clayton, Australia
| | - Jitraporn Vongsvivut
- Infrared Microspectroscopy (IRM) Beamline, ANSTO-Australian Synchrotron, Clayton, Australia
| | - Soon Hock Ng
- Optical Sciences Centre and ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), School of Science, Swinburne University of Technology, Hawthorn, Australia
| | - Meguya Ryu
- National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
| | - Mark J Tobin
- Infrared Microspectroscopy (IRM) Beamline, ANSTO-Australian Synchrotron, Clayton, Australia
| | - Saulius Juodkazis
- Optical Sciences Centre and ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), School of Science, Swinburne University of Technology, Hawthorn, Australia
| | - Junko Morikawa
- School of Materials and Chemical Technology, Tokyo Institute of Technology, Tokyo, Japan
| | - Bayden R Wood
- Centre for Biospectroscopy, School of Chemistry, Monash University, Clayton, Australia
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2
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Qiu C, Whittaker GR, Gellman SH, Daniel S, Abbott NL. Interactions of SARS-CoV-2 and MERS-CoV fusion peptides measured using single-molecule force methods. Biophys J 2023; 122:646-660. [PMID: 36650897 PMCID: PMC9841730 DOI: 10.1016/j.bpj.2023.01.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2022] [Revised: 08/07/2022] [Accepted: 01/12/2023] [Indexed: 01/19/2023] Open
Abstract
We address the challenge of understanding how hydrophobic interactions are encoded by fusion peptide (FP) sequences within coronavirus (CoV) spike proteins. Within the FPs of severe acute respiratory syndrome CoV 2 and Middle East respiratory syndrome CoV (MERS-CoV), a largely conserved peptide sequence called FP1 (SFIEDLLFNK and SAIEDLLFDK in SARS-2 and MERS, respectively) has been proposed to play a key role in encoding hydrophobic interactions that drive viral-host cell membrane fusion. Although a non-polar triad (Leu-Leu-Phe (LLF)) is common to both FP1 sequences, and thought to dominate the encoding of hydrophobic interactions, FP1 from SARS-2 and MERS differ in two residues (Phe 2 versus Ala 2 and Asn 9 versus Asp 9, respectively). Here we explore whether single-molecule force measurements can quantify hydrophobic interactions encoded by FP1 sequences, and then ask whether sequence variations between FP1 from SARS-2 and MERS lead to significant differences in hydrophobic interactions. We find that both SARS-2 and MERS wild-type FP1 generate measurable hydrophobic interactions at the single-molecule level, but that SARS-2 FP1 encodes a substantially stronger hydrophobic interaction than its MERS counterpart (1.91 ± 0.03 nN versus 0.68 ± 0.03 nN, respectively). By performing force measurements with FP1 sequences with single amino acid substitutions, we determine that a single-residue mutation (Phe 2 versus Ala 2) causes the almost threefold difference in the hydrophobic interaction strength generated by the FP1 of SARS-2 versus MERS, despite the presence of LLF in both sequences. Infrared spectroscopy and circular dichroism measurements support the proposal that the outsized influence of Phe 2 versus Ala 2 on the hydrophobic interaction arises from variation in the secondary structure adopted by FP1. Overall, these insights reveal how single-residue diversity in viral FPs, including FP1 of SARS-CoV-2 and MERS-CoV, can lead to substantial changes in intermolecular interactions proposed to play a key role in viral fusion, and hint at strategies for regulating hydrophobic interactions of peptides in a range of contexts.
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Affiliation(s)
- Cindy Qiu
- Robert F. Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York; Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York
| | - Gary R Whittaker
- Department of Microbiology and Immunology, Cornell University, Ithaca, New York
| | - Samuel H Gellman
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin
| | - Susan Daniel
- Robert F. Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York; Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York
| | - Nicholas L Abbott
- Robert F. Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York; Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York.
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Bazzone A, Tesmer L, Kurt D, Kaback HR, Fendler K, Madej MG. Investigation of sugar binding kinetics of the E. coli sugar/H + symporter XylE using solid supported membrane-based electrophysiology. J Biol Chem 2021; 298:101505. [PMID: 34929170 PMCID: PMC8784342 DOI: 10.1016/j.jbc.2021.101505] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Revised: 12/11/2021] [Accepted: 12/13/2021] [Indexed: 12/19/2022] Open
Abstract
Bacterial transporters are difficult to study using conventional electrophysiology because of their low transport rates and the small size of bacterial cells. Here, we applied solid-supported membrane–based electrophysiology to derive kinetic parameters of sugar translocation by the Escherichia coli xylose permease (XylE), including functionally relevant mutants. Many aspects of the fucose permease (FucP) and lactose permease (LacY) have also been investigated, which allow for more comprehensive conclusions regarding the mechanism of sugar translocation by transporters of the major facilitator superfamily. In all three of these symporters, we observed sugar binding and transport in real time to determine KM, Vmax, KD, and kobs values for different sugar substrates. KD and kobs values were attainable because of a conserved sugar-induced electrogenic conformational transition within these transporters. We also analyzed interactions between the residues in the available X-ray sugar/H+ symporter structures obtained with different bound sugars. We found that different sugars induce different conformational states, possibly correlating with different charge displacements in the electrophysiological assay upon sugar binding. Finally, we found that mutations in XylE altered the kinetics of glucose binding and transport, as Q175 and L297 are necessary for uncoupling H+ and d-glucose translocation. Based on the rates for the electrogenic conformational transition upon sugar binding (>300 s−1) and for sugar translocation (2 s−1 − 30 s−1 for different substrates), we propose a multiple-step mechanism and postulate an energy profile for sugar translocation. We also suggest a mechanism by which d-glucose can act as an inhibitor for XylE.
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Affiliation(s)
- Andre Bazzone
- Max-Planck-Institute of Biophysics, Department of Biophysical Chemistry in Frankfurt/M, Germany
| | - Laura Tesmer
- Max-Planck-Institute of Biophysics, Department of Biophysical Chemistry in Frankfurt/M, Germany
| | - Derya Kurt
- Max-Planck-Institute of Biophysics, Department of Biophysical Chemistry in Frankfurt/M, Germany
| | - H Ronald Kaback
- University of California, Department of Physiology and Department of Microbiology, Immunology, Molecular Genetics, Molecular Biology Institute in Los Angeles CA, USA
| | - Klaus Fendler
- Max-Planck-Institute of Biophysics, Department of Biophysical Chemistry in Frankfurt/M, Germany
| | - M Gregor Madej
- Institute of Biophysics and Biophysical Chemistry, Department of Structural Biology, University of Regensburg, Universitätsstr. 31, 95053 Regensburg, Germany; Institute of Biophysics, Department of Structural Biology, Saarland University, Center of Human and Molecular Biology, Building 60, 66421 Homburg, Germany
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Zanuy D, Puiggalí-Jou A, Conflitti P, Bocchinfuso G, Palleschi A, Alemán C. Aggregation propensity of therapeutic fibrin-homing pentapeptides: insights from experiments and molecular dynamics simulations. SOFT MATTER 2020; 16:10169-10179. [PMID: 33165494 DOI: 10.1039/d0sm00930j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
CREKA (Cys-Arg-Glu-Lys-Ala) and its engineered analogue CRMeEKA, in which Glu has been replaced by N-methyl-Glu to provide resistance against proteolysis, are emerging pentapeptides that were specifically designed to bind fibrin-fibronectin complexes accumulated in the walls of tumour vessels. However, many of the intrinsic properties of CREKA and CRMeEKA, which are probably responsible for their different behaviour when combined with other materials (such as polymers) for diagnosis and therapeutics, remain unknown yet. The intrinsic tendency of these pentapeptides to form aggregates has been analysed by combining experimental techniques and atomistic Molecular Dynamics (MD) simulations. Dynamic light scattering assays show the formation of nanoaggregates that increase in size with the peptide concentration, even though aggregation occurs sooner for CRMeEKA, independently of the peptide concentration. FTIR and circular dichroism spectroscopy studies suggest that aggregated pentapeptides do not adopt any secondary structure. Atomistic MD trajectories show that CREKA aggregates faster and forms bigger molecular clusters than CRMeEKA. This behaviour has been explained by stability of the conformations adopted by un-associated peptide strands. While CREKA molecules organize by forming intramolecular backbone - side chain hydrogen bonds, CRMeEKA peptides display main chain - main chain hydrogen bonds closing very stable γ- or β-turns. Besides, energetic analyses reveal that CRMeEKA strands are better solvated in water than CREKA ones, independent of whether they are assembled or un-associated.
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Affiliation(s)
- David Zanuy
- Department of Chemical Engineering and Barcelona Research Center in Multiscale Science and Engineering, Universitat Polytècnica de Catalunya, 08019 Barcelona, Spain.
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Abstract
Lactose permease is a paradigm for the major facilitator superfamily, the largest family of ion-coupled membrane transport proteins known at present. LacY carries out the coupled stoichiometric symport of a galactoside with an H+, using the free energy released from downhill translocation of H+ to drive accumulation of galactosides against a concentration gradient. In neutrophilic Escherichia coli, internal pH is kept at ∼7.6 over the physiological range, but the apparent pK (pKapp) for galactoside binding is 10.5. Surface-enhanced infrared absorption spectroscopy (SEIRAS) demonstrates that the high pKa is due to Glu325 (helix X), which must be protonated for LacY to bind galactoside effectively. Deprotonation is also obligatory for turnover, however. Here, we utilize SEIRAS to study the effect of mutating residues in the immediate vicinity of Glu325 on its pKa The results are consistent with the idea that Arg302 (helix IX) is important for deprotonation of Glu325.
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Oversized galactosides as a probe for conformational dynamics in LacY. Proc Natl Acad Sci U S A 2018; 115:4146-4151. [PMID: 29602806 DOI: 10.1073/pnas.1800706115] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Binding kinetics of α-galactopyranoside homologs with fluorescent aglycones of different sizes and shapes were determined with the lactose permease (LacY) of Escherichia coli by FRET from Trp151 in the binding site of LacY to the fluorophores. Fast binding was observed with LacY stabilized in an outward-open conformation (kon = 4-20 μM-1·s-1), indicating unobstructed access to the binding site even for ligands that are much larger than lactose. Dissociation rate constants (koff) increase with the size of the aglycone so that Kd values also increase but remain in the micromolar range for each homolog. Phe27 (helix I) forms an apparent constriction in the pathway for sugar by protruding into the periplasmic cavity. However, replacement of Phe27 with a bulkier Trp does not create an obstacle in the pathway even for large ligands, since binding kinetics remain unchanged. High accessibility of the binding site is also observed in a LacY/nanobody complex with partially blocked periplasmic opening. Remarkably, E. coli expressing WT LacY catalyzes transport of α- or β-galactopyranosides with oversized aglycones such as bodipy or Aldol518, which may require an extra space within the occluded intermediate. The results confirm that LacY specificity is strictly directed toward the galactopyranoside ring and also clearly indicate that the opening on the periplasmic side is sufficiently wide to accommodate the large galactoside derivatives tested here. We conclude that the actual pathway for the substrate entering from the periplasmic side is wider than the pore diameter calculated in the periplasmic-open X-ray structures.
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Guo R, Gaffney K, Yang Z, Kim M, Sungsuwan S, Huang X, Hubbell WL, Hong H. Steric trapping reveals a cooperativity network in the intramembrane protease GlpG. Nat Chem Biol 2016; 12:353-360. [PMID: 26999782 PMCID: PMC4837050 DOI: 10.1038/nchembio.2048] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2015] [Accepted: 01/22/2016] [Indexed: 12/21/2022]
Abstract
Membrane proteins are assembled through balanced interactions among protein, lipids and water. Studying their folding while maintaining the native lipid environment is necessary but challenging. Here we present methods for analyzing key elements in membrane protein folding including thermodynamic stability, compactness of the unfolded state and folding cooperativity under native conditions. The methods are based on steric trapping which couples unfolding of a doubly-biotinylated protein to binding of monovalent streptavidin (mSA). We further advanced this technology for general application by developing versatile biotin probes possessing spectroscopic reporters that are sensitized by mSA binding or protein unfolding. By applying these methods to an intramembrane protease GlpG of Escherichia coli, we elucidated a widely unraveled unfolded state, subglobal unfolding of the region encompassing the active site, and a network of cooperative and localized interactions to maintain the stability. These findings provide crucial insights into the folding energy landscape of membrane proteins.
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Affiliation(s)
- Ruiqiong Guo
- Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA
| | - Kristen Gaffney
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA
| | - Zhongyu Yang
- Jules Stein Eye Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA
| | - Miyeon Kim
- Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA
| | - Suttipun Sungsuwan
- Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA
| | - Xuefei Huang
- Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA
| | - Wayne L Hubbell
- Jules Stein Eye Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA
| | - Heedeok Hong
- Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.,Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA
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8
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Abstract
Lactose permease (LacY), a paradigm for the largest family of membrane transport proteins, catalyzes the coupled translocation of a galactoside and an H(+) across the Escherichia coli membrane (galactoside/H(+) symport). Initial X-ray structures reveal N- and C-terminal domains, each with six largely irregular transmembrane helices surrounding an aqueous cavity open to the cytoplasm. Recently, a structure with a narrow periplasmic opening and an occluded galactoside was obtained, confirming many observations and indicating that sugar binding involves induced fit. LacY catalyzes symport by an alternating access mechanism. Experimental findings garnered over 45 y indicate the following: (i) The limiting step for lactose/H(+) symport in the absence of the H(+) electrochemical gradient (∆µ̃H+) is deprotonation, whereas in the presence of ∆µ̃H+, the limiting step is opening of apo LacY on the other side of the membrane; (ii) LacY must be protonated to bind galactoside (the pK for binding is ∼10.5); (iii) galactoside binding and dissociation, not ∆µ̃H+, are the driving forces for alternating access; (iv) galactoside binding involves induced fit, causing transition to an occluded intermediate that undergoes alternating access; (v) galactoside dissociates, releasing the energy of binding; and (vi) Arg302 comes into proximity with protonated Glu325, causing deprotonation. Accumulation of galactoside against a concentration gradient does not involve a change in Kd for sugar on either side of the membrane, but the pKa (the affinity for H(+)) decreases markedly. Thus, transport is driven chemiosmotically but, contrary to expectation, ∆µ̃H+ acts kinetically to control the rate of the process.
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9
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Toward understanding driving forces in membrane protein folding. Arch Biochem Biophys 2014; 564:297-313. [DOI: 10.1016/j.abb.2014.07.031] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2014] [Revised: 07/21/2014] [Accepted: 07/23/2014] [Indexed: 12/13/2022]
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10
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Function, Structure, and Evolution of the Major Facilitator Superfamily: The LacY Manifesto. ACTA ACUST UNITED AC 2014. [DOI: 10.1155/2014/523591] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The major facilitator superfamily (MFS) is a diverse group of secondary transporters with members found in all kingdoms of life. A paradigm for MFS is the lactose permease (LacY) of Escherichia coli, which couples the stoichiometric translocation of a galactopyranoside and an H+ across the cytoplasmic membrane. LacY has been the test bed for the development of many methods applied for the analysis of transport proteins. X-ray structures of an inward-facing conformation and the most recent structure of an almost occluded conformation confirm many conclusions from previous studies. Although structure models are critical, they are insufficient to explain the catalysis of transport. The clues to understanding transport are based on the principles of enzyme kinetics. Secondary transport is a dynamic process—static snapshots of X-ray crystallography describe it only partially. However, without structural information, the underlying chemistry is virtually impossible to conclude. A large body of biochemical/biophysical data derived from systematic studies of site-directed mutants in LacY suggests residues critically involved in the catalysis, and a working model for the symport mechanism that involves alternating access of the binding site is presented. The general concepts derived from the bacterial LacY are examined for their relevance to other MFS transporters.
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11
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Abstract
The lactose permease (LacY) of Escherichia coli, a paradigm for the major facilitator superfamily, catalyzes the coupled stoichiometric translocation of a galactopyranoside and an H(+) across the cytoplasmic membrane. To catalyze transport, LacY undergoes large conformational changes that allow alternating access of sugar- and H(+)-binding sites to either side of the membrane. Despite strong evidence for an alternating access mechanism, it remains unclear how H(+)- and sugar-binding trigger the cascade of interactions leading to alternating conformational states. Here we used dynamic single-molecule force spectroscopy to investigate how substrate binding induces this phenomenon. Galactoside binding strongly modifies kinetic, energetic, and mechanical properties of the N-terminal 6-helix bundle of LacY, whereas the C-terminal 6-helix bundle remains largely unaffected. Within the N-terminal 6-helix bundle, the properties of helix V, which contains residues critical for sugar binding, change most radically. Particularly, secondary structures forming the N-terminal domain exhibit mechanically brittle properties in the unbound state, but highly flexible conformations in the substrate-bound state with significantly increased lifetimes and energetic stability. Thus, sugar binding tunes the properties of the N-terminal domain to initiate galactoside/H(+) symport. In contrast to wild-type LacY, the properties of the conformationally restricted mutant Cys154→Gly do not change upon sugar binding. It is also observed that the single mutation of Cys154→Gly alters intramolecular interactions so that individual transmembrane helices manifest different properties. The results support a working model of LacY in which substrate binding induces alternating conformational states and provides insight into their specific kinetic, energetic, and mechanical properties.
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12
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Quaroni L, Zlateva T, Sarafimov B, Kreuzer HW, Wehbe K, Hegg EL, Cinque G. Synchrotron based infrared imaging and spectroscopy via focal plane array on live fibroblasts in D2O enriched medium. Biophys Chem 2014; 189:40-8. [PMID: 24747675 DOI: 10.1016/j.bpc.2014.03.002] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Revised: 03/15/2014] [Accepted: 03/16/2014] [Indexed: 12/29/2022]
Abstract
We successfully tested the viability of using synchrotron-based full-field infrared imaging to study biochemical processes inside living cells. As a model system, we studied fibroblast cells exposed to a medium highly enriched with D2O. We could show that the experimental technique allows us to reproduce at the cellular level measurements that are normally performed on purified biological molecules. We can obtain information about lipid conformation and distribution, kinetics of hydrogen/deuterium exchange, and the formation of concentration gradients of H and O isotopes in water that are associated with cell metabolism. The implementation of the full field technique in a sequential imaging format gives a description of cellular biochemistry and biophysics that contains both spatial and temporal information.
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Affiliation(s)
- Luca Quaroni
- Paul Scherrer Institut, Villigen-PSI, CH-5232, Switzerland.
| | | | | | - Helen W Kreuzer
- Pacific Northwest National Laboratory, Richland, WA 99354, USA
| | - Katia Wehbe
- Diamond Light Source, Harwell Campus, Chilton-Didcot, Oxon OX11 0DE, UK
| | - Eric L Hegg
- Michigan State University, Department of Biochemistry & Molecular Biology, East Lansing, MI 48824, USA
| | - Gianfelice Cinque
- Diamond Light Source, Harwell Campus, Chilton-Didcot, Oxon OX11 0DE, UK
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13
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Stelzl LS, Fowler PW, Sansom MS, Beckstein O. Flexible gates generate occluded intermediates in the transport cycle of LacY. J Mol Biol 2014; 426:735-51. [PMID: 24513108 PMCID: PMC3905165 DOI: 10.1016/j.jmb.2013.10.024] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Revised: 10/17/2013] [Accepted: 10/18/2013] [Indexed: 12/29/2022]
Abstract
The major facilitator superfamily (MFS) transporter lactose permease (LacY) alternates between cytoplasmic and periplasmic open conformations to co-transport a sugar molecule together with a proton across the plasma membrane. Indirect experimental evidence suggested the existence of an occluded transition intermediate of LacY, which would prevent leaking of the proton gradient. As no experimental structure is known, the conformational transition is not fully understood in atomic detail. We simulated transition events from a cytoplasmic open conformation to a periplasmic open conformation with the dynamic importance sampling molecular dynamics method and observed occluded intermediates. Analysis of water permeation pathways and the electrostatic free-energy landscape of a solvated proton indicated that the occluded state contains a solvated central cavity inaccessible from either side of the membrane. We propose a pair of geometric order parameters that capture the state of the pathway through the MFS transporters as shown by a survey of available crystal structures and models. We present a model for the occluded state of apo-LacY, which is similar to the occluded crystal structures of the MFS transporters EmrD, PepTSo, NarU, PiPT and XylE. Our simulations are consistent with experimental double electron spin–spin distance measurements that have been interpreted to show occluded conformations. During the simulations, a salt bridge that has been postulated to be involved in driving the conformational transition formed. Our results argue against a simple rigid-body domain motion as implied by a strict “rocker-switch mechanism” and instead hint at an intricate coupling between two flexible gates. The transport mechanism of LacY is hypothesized to involve an intermediate “occluded” state. Such a state is observed in computer simulations of the conformational transitions. Simulation data are validated with experimental double electron–electron spin resonance measurements. The structural gating elements of LacY are identified. Occluded LacY is similar to known occluded structures of homologous proteins.
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Affiliation(s)
- Lukas S. Stelzl
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Philip W. Fowler
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Mark S.P. Sansom
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Oliver Beckstein
- Center for Biological Physics, Department of Physics, Arizona State University, Tempe, AZ 85287, USA
- Corresponding author Department of Physics, Center for Biological Physics, Arizona State University, P.O. Box 871504, Tempe, AZ 85287-1504, USA.
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14
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Rockenstein E, Nuber S, Overk CR, Ubhi K, Mante M, Patrick C, Adame A, Trejo-Morales M, Gerez J, Picotti P, Jensen PH, Campioni S, Riek R, Winkler J, Gage FH, Winner B, Masliah E. Accumulation of oligomer-prone α-synuclein exacerbates synaptic and neuronal degeneration in vivo. ACTA ACUST UNITED AC 2014; 137:1496-513. [PMID: 24662516 DOI: 10.1093/brain/awu057] [Citation(s) in RCA: 171] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
In Parkinson's disease and dementia with Lewy bodies, α-synuclein aggregates to form oligomers and fibrils; however, the precise nature of the toxic α-synuclein species remains unclear. A number of synthetic α-synuclein mutations were recently created (E57K and E35K) that produce species of α-synuclein that preferentially form oligomers and increase α-synuclein-mediated toxicity. We have shown that acute lentiviral expression of α-synuclein E57K leads to the degeneration of dopaminergic neurons; however, the effects of chronic expression of oligomer-prone α-synuclein in synapses throughout the brain have not been investigated. Such a study could provide insight into the possible mechanism(s) through which accumulation of α-synuclein oligomers in the synapse leads to neurodegeneration. For this purpose, we compared the patterns of neurodegeneration and synaptic damage between a newly generated mThy-1 α-synuclein E57K transgenic mouse model that is prone to forming oligomers and the mThy-1 α-synuclein wild-type mouse model (Line 61), which accumulates various forms of α-synuclein. Three lines of α-synuclein E57K (Lines 9, 16 and 54) were generated and compared with the wild-type. The α-synuclein E57K Lines 9 and 16 were higher expressings of α-synuclein, similar to α-synuclein wild-type Line 61, and Line 54 was a low expressing of α-synuclein compared to Line 61. By immunoblot analysis, the higher-expressing α-synuclein E57K transgenic mice showed abundant oligomeric, but not fibrillar, α-synuclein whereas lower-expressing mice accumulated monomeric α-synuclein. Monomers, oligomers, and fibrils were present in α-synuclein wild-type Line 61. Immunohistochemical and ultrastructural analyses demonstrated that α-synuclein accumulated in the synapses but not in the neuronal cells bodies, which was different from the α-synuclein wild-type Line 61, which accumulates α-synuclein in the soma. Compared to non-transgenic and lower-expressing mice, the higher-expressing α-synuclein E57K mice displayed synaptic and dendritic loss, reduced levels of synapsin 1 and synaptic vesicles, and behavioural deficits. Similar alterations, but to a lesser extent, were seen in the α-synuclein wild-type mice. Moreover, although the oligomer-prone α-synuclein mice displayed neurodegeneration in the frontal cortex and hippocampus, the α-synuclein wild-type only displayed neuronal loss in the hippocampus. These results support the hypothesis that accumulating oligomeric α-synuclein may mediate early synaptic pathology in Parkinson's disease and dementia with Lewy bodies by disrupting synaptic vesicles. This oligomer-prone model might be useful for evaluating therapies directed at oligomer reduction.
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Affiliation(s)
- Edward Rockenstein
- 1 Department of Neurosciences, University of California San Diego, La Jolla, CA, USA
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15
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Kumar H, Kasho V, Smirnova I, Finer-Moore JS, Kaback HR, Stroud RM. Structure of sugar-bound LacY. Proc Natl Acad Sci U S A 2014; 111:1784-8. [PMID: 24453216 PMCID: PMC3918835 DOI: 10.1073/pnas.1324141111] [Citation(s) in RCA: 102] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Here we describe the X-ray crystal structure of a double-Trp mutant (Gly46→Trp/Gly262→Trp) of the lactose permease of Escherichia coli (LacY) with a bound, high-affinity lactose analog. Although thought to be arrested in an open-outward conformation, the structure is almost occluded and is partially open to the periplasmic side; the cytoplasmic side is tightly sealed. Surprisingly, the opening on the periplasmic side is sufficiently narrow that sugar cannot get in or out of the binding site. Clearly defined density for a bound sugar is observed at the apex of the almost occluded cavity in the middle of the protein, and the side chains shown to ligate the galactopyranoside strongly confirm more than two decades of biochemical and spectroscopic findings. Comparison of the current structure with a previous structure of LacY with a covalently bound inactivator suggests that the galactopyranoside must be fully ligated to induce an occluded conformation. We conclude that protonated LacY binds D-galactopyranosides specifically, inducing an occluded state that can open to either side of the membrane.
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Affiliation(s)
- Hemant Kumar
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158; and
| | | | | | - Janet S. Finer-Moore
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158; and
| | - H. Ronald Kaback
- Departments of Physiology
- Microbiology, Immunology and Molecular Genetics, and
- Molecular Biology Institute, University of California, Los Angeles, CA 90095
| | - Robert M. Stroud
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158; and
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16
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The Life and Times of Lac Permease: Crystals Ain’t Everything, but They Certainly Do Help. SPRINGER SERIES IN BIOPHYSICS 2014. [DOI: 10.1007/978-3-642-53839-1_6] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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17
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Abstract
One fundamentally important problem for understanding the mechanism of coupling between substrate and H(+) translocation with secondary active transport proteins is the identification and physical localization of residues involved in substrate and H(+) binding. This information is exceptionally difficult to obtain with the Major Facilitator Superfamily (MFS) because of the broad sequence diversity of the members. The MFS is the largest and most diverse group of transporters, many of which are clinically important, and includes members from all kingdoms of life. A wide range of substrates is transported, in many instances against a concentration gradient by transduction of the energy stored in an H(+) electrochemical gradient using symport mechanisms, which are discussed herein. Crystallographic structures of MFS members indicate that a deep central hydrophilic cavity surrounded by 12 mostly irregular transmembrane helices represents a common structural feature. An inverted triple-helix structural symmetry motif within the N- and C-terminal six-helix bundles suggests that the proteins may have arisen by intragenic multiplication. In the work presented here, the triple-helix motifs are aligned in combinatorial fashion so as to detect functionally homologous positions with known atomic structures of MFS members. Substrate and H(+)-binding sites in symporters that transport substrates, ranging from simple ions like phosphate to more complex peptides or disaccharides, are found to be in similar locations. It also appears likely that there is a homologous ordered kinetic mechanism for the H(+)-coupled MFS symporters.
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18
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Gaiko O, Bazzone A, Fendler K, Kaback HR. Electrophysiological characterization of uncoupled mutants of LacY. Biochemistry 2013; 52:8261-6. [PMID: 24152072 DOI: 10.1021/bi4013269] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
In this study of the lactose permease of Escherichia coli (LacY), five functionally irreplaceable residues involved specifically in H(+) translocation (Arg302 and Glu325) or in the coupling between protonation and sugar binding (Tyr236, Glu269, and His322) were mutated individually or together with mutant Glu325 → Ala. The wild type and each mutant were purified and reconstituted into proteoliposomes, which were then examined using solid-supported-membrane-based electrophysiology. Mutants Glu325 → Ala or Arg302 → Ala, in which H(+) symport is abolished, exhibit a weakly electrogenic rapid reaction triggered by sugar binding. The reaction is essentially absent in mutant Tyr236 → Phe, Glu269 → Ala, and His322 → Ala, and each of these mutations blocks the electrogenic reaction observed in the Glu325 → Ala mutant. The findings are consistent with the interpretation that the electrogenic reaction induced by sugar binding is due to rearrangement of charged residues in LacY and that this reaction is blocked by mutation of each member of the Tyr236/Glu269/His322 triad. In addition, further support is provided for the conclusion that deprotonation is rate limiting for downhill lactose/H(+) symport.
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Affiliation(s)
- Olga Gaiko
- Departments of Physiology and ‡Microbiology, Immunology & Molecular Genetics, §Molecular Biology Institute, University of California-Los Angeles , Los Angeles, California 90095, United States
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19
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Trp replacements for tightly interacting Gly-Gly pairs in LacY stabilize an outward-facing conformation. Proc Natl Acad Sci U S A 2013; 110:8876-81. [PMID: 23671103 DOI: 10.1073/pnas.1306849110] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Trp replacements for conserved Gly-Gly pairs between the N- and C-terminal six-helix bundles on the periplasmic side of lactose permease (LacY) cause complete loss of transport activity with little or no effect on sugar binding. Moreover, the detergent-solubilized mutants exhibit much greater thermal stability than WT LacY. A Cys replacement for Asn245, which is inaccessible/unreactive in WT LacY, alkylates readily in the Gly→Trp mutants, indicating that the periplasmic cavity is patent. Stopped-flow kinetic measurements of sugar binding with the Gly→Trp mutants in detergent reveal linear dependence of binding rates on sugar concentration, as observed with WT or the C154G mutant of LacY, and are compatible with free access to the sugar-binding site in the middle of the molecule. Remarkably, after reconstitution of the Gly→Trp mutants into proteoliposomes, the concentration dependence of sugar-binding rates increases sharply with even faster rates than measured in detergent. Such behavior is strikingly different from that observed for reconstituted WT LacY, in which sugar-binding rates are independent of sugar concentration because opening of the periplasmic cavity is limiting for sugar binding. The observations clearly indicate that Gly→Trp replacements, which introduce bulky residues into tight Gly-Gly interdomain interactions on the periplasmic side of LacY, prevent closure of the periplasmic cavity and, as a result, shift the distribution of LacY toward an outward-open conformation.
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20
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Abstract
Integral membrane proteins reside within the bilayer membranes that surround cells and organelles, playing critical roles in movement of molecules across them and the transduction of energy and signals. While their extreme amphipathicity presents technical challenges, biological mass spectrometry has been applied to all aspects of membrane protein chemistry and biology, including analysis of primary, secondary, tertiary, and quaternary structures as well as the dynamics that accompany functional cycles and catalysis.
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Affiliation(s)
- Julian P Whitelegge
- The Pasarow Mass Spectrometry Laboratory, The NPI-Semel Institute for Neuroscience and Human Behavior, The David Geffen School of Medicine, University of California, Los Angeles, 760 Westwood Plaza, Los Angeles, California 90095, United States.
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21
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Zhang C, Myers J, Chen Z. Elucidation of molecular structures at buried polymer interfaces and biological interfaces using sum frequency generation vibrational spectroscopy. SOFT MATTER 2013; 9:4738-4761. [PMID: 23710244 PMCID: PMC3661304 DOI: 10.1039/c3sm27710k] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Sum frequency generation (SFG) vibrational spectroscopy has been developed into an important technique to study surfaces and interfaces. It can probe buried interfaces in situ and provide molecular level structural information such as the presence of various chemical moieties, quantitative molecular functional group orientation, and time dependent kinetics or dynamics at such interfaces. This paper focuses on these three most important advantages of SFG and reviews some of the recent progress in SFG studies on interfaces related to polymer materials and biomolecules. The results discussed here demonstrate that SFG can provide important molecular structural information of buried interfaces in situ and in real time, which is difficult to obtain by other surface sensitive analytical techniques.
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Affiliation(s)
- Chi Zhang
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
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22
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Furutani Y, Shimizu H, Asai Y, Fukuda T, Oiki S, Kandori H. ATR-FTIR Spectroscopy Revealing the Different Vibrational Modes of the Selectivity Filter Interacting with K(+) and Na(+) in the Open and Collapsed Conformations of the KcsA Potassium Channel. J Phys Chem Lett 2012; 3:3806-3810. [PMID: 26291114 DOI: 10.1021/jz301721f] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The potassium channel is highly selective for K(+) over Na(+), and the selectivity filter binds multiple dehydrated K(+) ions upon permeation. Here, we applied attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy to extract ion-binding-induced signals of the KcsA potassium channel at neutral pH. Shifts in the peak of the amide-I signal towards lower vibrational frequencies were observed as K(+) was replaced with Na(+). These ion species-specific shifts deduced the selectivity filter as the source of the signal, which was supported by the spectra of a mutant for the selectivity filter (Y78F). The difference FTIR spectra between the solution containing various concentrations of K(+) and that containing pure Na(+) demonstrated two types of peak shifts of the amide-I vibration in response to the K(+) concentration. These signals represent the binding of K(+) ions to the different sites in the selectivity filter with different dissociation constants (KD = 9 or 18 mM).
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Affiliation(s)
- Yuji Furutani
- †Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan
- §Division of Biomolecular Sensing, Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan
| | - Hirofumi Shimizu
- ‡Department of Molecular Physiology and Biophysics, Faculty of Medical Sciences, University of Fukui, Yoshida, 910-1193 Fukui, Japan
| | - Yusuke Asai
- †Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan
| | - Tetsuya Fukuda
- †Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan
| | - Shigetoshi Oiki
- ‡Department of Molecular Physiology and Biophysics, Faculty of Medical Sciences, University of Fukui, Yoshida, 910-1193 Fukui, Japan
| | - Hideki Kandori
- †Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan
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23
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Apo-intermediate in the transport cycle of lactose permease (LacY). Proc Natl Acad Sci U S A 2012; 109:E2970-8. [PMID: 23012238 DOI: 10.1073/pnas.1211183109] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The lactose permease (LacY) catalyzes coupled stoichiometric symport of a galactoside and an H(+). Crystal structures reveal 12, mostly irregular, transmembrane α-helices surrounding a cavity with sugar- and H(+)- binding sites at the apex, which is accessible from the cytoplasm and sealed on the periplasmic side (an inward-facing conformer). An outward-facing model has also been proposed based on biochemical and spectroscopic measurements, as well as the X-ray structure of a related symporter. Converging lines of evidence demonstrate that LacY functions by an alternating access mechanism. Here, we generate a model for an apo-intermediate of LacY based on crystallographic coordinates of LacY and the oligopeptide/H(+) symporter. The model exhibits a conformation with an occluded cavity inaccessible from either side of the membrane. Furthermore, kinetic considerations and double electron-electron resonance measurements suggest that another occluded conformer with bound sugar exists during turnover. An energy profile for symport is also presented.
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24
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Role of the irreplaceable residues in the LacY alternating access mechanism. Proc Natl Acad Sci U S A 2012; 109:12438-42. [PMID: 22802658 DOI: 10.1073/pnas.1210684109] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Few side chains in the galactoside/H(+) symporter LacY (lactose permease of Escherichia coli) are irreplaceable for an alternating access mechanism in which sugar binding induces closing of the cytoplasmic cavity and reciprocal opening of a periplasmic cavity. In this study, each irreplaceable residue was mutated individually, and galactoside-induced opening or closing of periplasmic or cytoplasmic cavities was probed by site-directed alkylation. Mutation of Glu126 (helix IV) or Arg144 (helix V), which are essential for sugar binding, completely blocks sugar-induced periplasmic opening as expected. Remarkably, however, replacement of Glu269 (helix VIII), His322 (helix X), or Tyr236 (helix VII) causes spontaneous opening of the periplasmic cavity in the absence of sugar and decreased closing of the cytoplasmic cavity in the presence of galactoside. In contrast, mutation of Arg302 (helix IX) or Glu325 (helix X) has no such effect, and sugar binding induces normal opening and closing of periplasmic and cytoplasmic cavities. Possibly, Glu269, His322, and Tyr236 act in concert to coordinate opening and closing of the cavities by binding water, which also acts as a cofactor in H(+) translocation. Mutation of the triad results in loss of the bound water, which destabilizes LacY, and the cavities open and close in an uncoordinated manner. Thus, the triad mutants exhibit poor affinity for sugar, and galactoside/H(+) symport is abolished as well.
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25
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Dynamics of a bacterial multidrug ABC transporter in the inward- and outward-facing conformations. Proc Natl Acad Sci U S A 2012; 109:10832-6. [PMID: 22711831 DOI: 10.1073/pnas.1204067109] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The study of membrane proteins remains a challenging task, and approaches to unravel their dynamics are scarce. Here, we applied hydrogen/deuterium exchange (HDX) coupled to mass spectrometry to probe the motions of a bacterial multidrug ATP-binding cassette (ABC) transporter, BmrA, in the inward-facing (resting state) and outward-facing (ATP-bound) conformations. Trypsin digestion and global or local HDX support the transition between inward- and outward-facing conformations during the catalytic cycle of BmrA. However, in the resting state, peptides from the two intracellular domains, especially ICD2, show a much faster HDX than in the closed state. This shows that these two subdomains are very flexible in this conformation. Additionally, molecular dynamics simulations suggest a large fluctuation of the Cα positions from ICD2 residues in the inward-facing conformation of a related transporter, MsbA. These results highlight the unexpected flexibility of ABC exporters in the resting state and underline the power of HDX coupled to mass spectrometry to explore conformational changes and dynamics of large membrane proteins.
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26
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Liu Y, Jasensky J, Chen Z. Molecular interactions of proteins and peptides at interfaces studied by sum frequency generation vibrational spectroscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:2113-21. [PMID: 22171656 PMCID: PMC3269552 DOI: 10.1021/la203823t] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Interfacial peptides and proteins are critical in many biological processes and thus are of interest to various research fields. To study these processes, surface sensitive techniques are required to completely describe different interfacial interactions intrinsic to many complicated processes. Sum frequency generation (SFG) spectroscopy has been developed into a powerful tool to investigate these interactions and mechanisms of a variety of interfacial peptides and proteins. It has been shown that SFG has intrinsic surface sensitivity and the ability to acquire conformation, orientation, and ordering information about these systems. This paper reviews recent studies on peptide/protein-substrate interactions, peptide/protein-membrane interactions, and protein complexes at interfaces and demonstrates the ability of SFG on unveiling the molecular pictures of complicated interfacial biological processes.
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Affiliation(s)
- Yuwei Liu
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, MI 48109 USA
| | - Joshua Jasensky
- Department of Biophysics, University of Michigan, 930 North University Avenue, Ann Arbor, MI 48109 USA
| | - Zhan Chen
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, MI 48109 USA
- Department of Biophysics, University of Michigan, 930 North University Avenue, Ann Arbor, MI 48109 USA
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27
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Smirnova I, Kasho V, Kaback HR. Lactose permease and the alternating access mechanism. Biochemistry 2011; 50:9684-93. [PMID: 21995338 DOI: 10.1021/bi2014294] [Citation(s) in RCA: 97] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Crystal structures of the lactose permease of Escherichia coli (LacY) reveal 12, mostly irregular transmembrane α-helices surrounding a large cavity open to the cytoplasm and a tightly sealed periplasmic side (inward-facing conformation) with the sugar-binding site at the apex of the cavity and inaccessible from the periplasm. However, LacY is highly dynamic, and binding of a galactopyranoside causes closing of the inward-facing cavity with opening of a complementary outward-facing cavity. Therefore, the coupled, electrogenic translocation of a sugar and a proton across the cytoplasmic membrane via LacY very likely involves a global conformational change that allows alternating access of sugar- and H(+)-binding sites to either side of the membrane. Here the various biochemical and biophysical approaches that provide strong support for the alternating access mechanism are reviewed. Evidence is also presented indicating that opening of the periplasmic cavity is probably the limiting step for binding and perhaps transport.
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Affiliation(s)
- Irina Smirnova
- Department of Physiology and Department of Microbiology, University of California, Los Angeles, California 90095, United States
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28
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Zhou Y, Madej MG, Guan L, Nie Y, Kaback HR. An early event in the transport mechanism of LacY protein: interaction between helices V and I. J Biol Chem 2011; 286:30415-30422. [PMID: 21730060 DOI: 10.1074/jbc.m111.268433] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Helix V in LacY, which abuts and crosses helix I in the N-terminal helix bundle of LacY, contains Arg(144) and Trp(151), two residues that play direct roles in sugar recognition and binding, as well as Cys(154), which is important for conformational flexibility. In this study, paired Cys replacement mutants in helices V and I were strategically constructed with tandem factor Xa protease cleavage sites in the loop between the two helices to test cross-linking. None of the mutants form disulfides spontaneously; however, three mutants (Pro(28) → Cys/Cys(154), Pro(28) → Cys/Val(158) → Cys, and Phe(29) → Cys/Val(158) → Cys) exhibit cross-linking after treatment with copper/1,10-phenanthroline (Cu/Ph) or 1,1-methanediyl bismethanethiosulfonate ((MTS)(2)-1), 3-4 Å), and cross-linking is quantitative in the presence of ligand. Remarkably, with one mutant, complete cross-linking with (MTS)(2)-1 has no effect on lactose transport, whereas quantitative disulfide cross-linking catalyzed by Cu/Ph markedly inhibits transport activity. The findings are consistant with a number of previous conclusions suggesting that sugar binding to LacY causes a localized scissors-like movement between helices V and I near the point where the two helices cross in the middle of the membrane. This ligand-induced movement may act to initiate the global conformational change resulting from sugar binding.
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Affiliation(s)
- Yonggang Zhou
- Departments of Physiology, University of California, Los Angeles, California 90095-1662
| | - M Gregor Madej
- Departments of Physiology, University of California, Los Angeles, California 90095-1662
| | - Lan Guan
- Departments of Physiology, University of California, Los Angeles, California 90095-1662
| | - Yiling Nie
- Departments of Physiology, University of California, Los Angeles, California 90095-1662
| | - H Ronald Kaback
- Departments of Physiology, University of California, Los Angeles, California 90095-1662; Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, California 90095-1662; Molecular Biology Institute, University of California, Los Angeles, California 90095-1662.
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29
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Radestock S, Forrest LR. The alternating-access mechanism of MFS transporters arises from inverted-topology repeats. J Mol Biol 2011; 407:698-715. [PMID: 21315728 DOI: 10.1016/j.jmb.2011.02.008] [Citation(s) in RCA: 151] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2010] [Revised: 01/16/2011] [Accepted: 02/02/2011] [Indexed: 11/19/2022]
Abstract
Lactose permease (LacY) is the prototype of the major facilitator superfamily (MFS) of secondary transporters. Available structures of LacY reveal a state in which the substrate is exposed to the cytoplasm but is occluded from the periplasm. However, the alternating-access transport mechanism requires the existence of a periplasm-facing state. We recently showed that inverted-topology structural repeats provide the foundation for the mechanisms of two transporter families with folds distinct from the MFS. Here, we generated a structural model of LacY by swapping the conformations of inverted-topology repeats identified in its two domains. The model exhibits all required properties of an outward-facing conformation, i.e., closure of the binding site to the cytoplasm and exposure to the periplasm. Furthermore, the model agrees with double electron-electron resonance distance changes, accessibility to cysteine-modifying reagents, cysteine cross-linking data, and a recent structure of a distantly related transporter. Analysis of the intradomain differences between the two states suggests a role for conserved sequence motifs in occluding the central pathway through kinking of the pore-lining helices. In addition, predicted re-pairing of critical salt-bridging residues in the binding sites agrees remarkably well with previous proposals, allowing a description of the proton/sugar transport mechanism. More fundamentally, our model demonstrates that inverted-topology repeats provide the foundation for the alternating-access mechanisms of MFS transporters.
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Affiliation(s)
- Sebastian Radestock
- Computational Structural Biology Group, Max Planck Institute of Biophysics, Max-von-Laue-Str. 3, 60438 Frankfurtam Main, Germany
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30
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Abstract
Lactose permease of Escherichia coli (LacY) is highly dynamic, and sugar binding causes closing of a large inward-facing cavity with opening of a wide outward-facing hydrophilic cavity. Therefore, lactose/H+ symport via LacY very likely involves a global conformational change that allows alternating access of single sugar- and H+-binding sites to either side of the membrane. Here, in honor of Stephan H. White’s seventieth birthday, we review in camera the various biochemical/biophysical approaches that provide experimental evidence for the alternating access mechanism.
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31
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Wang SC, Politis A, Di Bartolo N, Bavro VN, Tucker SJ, Booth PJ, Barrera NP, Robinson CV. Ion Mobility Mass Spectrometry of Two Tetrameric Membrane Protein Complexes Reveals Compact Structures and Differences in Stability and Packing. J Am Chem Soc 2010; 132:15468-70. [DOI: 10.1021/ja104312e] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Sheila C. Wang
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, U.K., Department of Biochemistry, University of Bristol, Bristol BS8 1TD, U.K., Department of Physics, University of Oxford, Clarendon Laboratory, Oxford OX1 3PU, U.K., and Department of Physiology, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
| | - Argyris Politis
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, U.K., Department of Biochemistry, University of Bristol, Bristol BS8 1TD, U.K., Department of Physics, University of Oxford, Clarendon Laboratory, Oxford OX1 3PU, U.K., and Department of Physiology, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
| | - Natalie Di Bartolo
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, U.K., Department of Biochemistry, University of Bristol, Bristol BS8 1TD, U.K., Department of Physics, University of Oxford, Clarendon Laboratory, Oxford OX1 3PU, U.K., and Department of Physiology, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
| | - Vassiliy N. Bavro
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, U.K., Department of Biochemistry, University of Bristol, Bristol BS8 1TD, U.K., Department of Physics, University of Oxford, Clarendon Laboratory, Oxford OX1 3PU, U.K., and Department of Physiology, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
| | - Stephen J. Tucker
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, U.K., Department of Biochemistry, University of Bristol, Bristol BS8 1TD, U.K., Department of Physics, University of Oxford, Clarendon Laboratory, Oxford OX1 3PU, U.K., and Department of Physiology, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
| | - Paula J. Booth
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, U.K., Department of Biochemistry, University of Bristol, Bristol BS8 1TD, U.K., Department of Physics, University of Oxford, Clarendon Laboratory, Oxford OX1 3PU, U.K., and Department of Physiology, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
| | - Nelson P. Barrera
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, U.K., Department of Biochemistry, University of Bristol, Bristol BS8 1TD, U.K., Department of Physics, University of Oxford, Clarendon Laboratory, Oxford OX1 3PU, U.K., and Department of Physiology, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
| | - Carol V. Robinson
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, U.K., Department of Biochemistry, University of Bristol, Bristol BS8 1TD, U.K., Department of Physics, University of Oxford, Clarendon Laboratory, Oxford OX1 3PU, U.K., and Department of Physiology, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
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32
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Sugar binding induces the same global conformational change in purified LacY as in the native bacterial membrane. Proc Natl Acad Sci U S A 2010; 107:9903-8. [PMID: 20457922 DOI: 10.1073/pnas.1004515107] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Many independent lines of evidence indicate that the lactose permease of Escherichia coli (LacY) is highly dynamic and that sugar binding causes closing of a large inward-facing cavity with opening of a wide outward-facing hydrophilic cavity. Therefore, lactose/H(+) symport catalyzed by LacY very likely involves a global conformational change that allows alternating access of single sugar- and H(+)-binding sites to either side of the membrane (the alternating access model). The x-ray crystal structures of LacY, as well as the majority of spectroscopic studies, use purified protein in detergent micelles. By using site-directed alkylation, we now demonstrate that sugar binding induces virtually the same global conformational change in LacY whether the protein is in the native bacterial membrane or is solubilized and purified in detergent. The results also indicate that the x-ray crystal structure reflects the structure of wild-type LacY in the native membrane in the absence of sugar.
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33
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Cieslak JA, Focia PJ, Gross A. Electron spin-echo envelope modulation (ESEEM) reveals water and phosphate interactions with the KcsA potassium channel. Biochemistry 2010; 49:1486-94. [PMID: 20092291 DOI: 10.1021/bi9016523] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Electron spin-echo envelope modulation (ESEEM) spectroscopy is a well-established technique for the study of naturally occurring paramagnetic metal centers. The technique has been used to study copper complexes, hemes, enzyme mechanisms, micellar water content, and water permeation profiles in membranes, among other applications. In the present study, we combine ESEEM spectroscopy with site-directed spin labeling (SDSL) and X-ray crystallography in order to evaluate the technique's potential as a structural tool to describe the native environment of membrane proteins. Using the KcsA potassium channel as a model system, we demonstrate that deuterium ESEEM can detect water permeation along the lipid-exposed surface of the KcsA outer helix. We further demonstrate that (31)P ESEEM is able to identify channel residues that interact with the phosphate headgroup of the lipid bilayer. In combination with X-ray crystallography, the (31)P data may be used to define the phosphate interaction surface of the protein. The results presented here establish ESEEM as a highly informative technique for SDSL studies of membrane proteins.
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Affiliation(s)
- John A Cieslak
- Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Feinberg School of Medicine, 303 East Chicago Avenue, Chicago, Illinois 60611, USA
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34
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Zhou Y, Nie Y, Kaback HR. Residues gating the periplasmic pathway of LacY. J Mol Biol 2009; 394:219-25. [PMID: 19781551 DOI: 10.1016/j.jmb.2009.09.043] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2009] [Revised: 09/16/2009] [Accepted: 09/17/2009] [Indexed: 11/16/2022]
Abstract
X-ray crystal structures of LacY (lactose permease of Escherichia coli) exhibit a large cytoplasmic cavity containing the residues involved in sugar binding and H(+) translocation at the apex and a tightly packed side facing the periplasm. However, biochemical and biophysical evidence provide a strong indication that a hydrophilic pathway opens on the external surface of LacY with closing of the cytoplasmic side upon sugar binding. Thus, an alternating-access mechanism in which sugar- and H(+)-binding sites at the approximate middle of the molecule are alternatively exposed to either side of the membrane is likely to underlie LacY-catalyzed sugar/H(+) symport. To further investigate periplasmic opening, we replaced paired residues on the tightly packed periplasmic side of LacY with Cys, and the effect of cross-linking was studied by testing the accessibility/reactivity of Cys148 with the elongated ( approximately 29 A), impermeant hydrophilic reagent maleimide-PEG2-biotin. When the paired-Cys mutant Ile40-->Cys/Asn245-->Cys containing native Cys148 is oxidized to form a disulfide bond, the reactivity of Cys148 is markedly inhibited. Moreover, the reactivity of Cys148 in this mutant increases with the length of the cross-linking agent. In contrast, maleimide-PEG2-biotin reactivity of Cys148 is unaffected by oxidation of two other paired-Cys mutants at the mouth of the periplasmic cavity. The data indicate that residues Ile40 and Asn245 play a primary role in gating the periplasmic cavity and provide further support for the alternating-access model.
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Affiliation(s)
- Yonggang Zhou
- Department of Physiology, University of California, Los Angeles, CA 90095-7327, USA
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35
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Langosch D, Arkin IT. Interaction and conformational dynamics of membrane-spanning protein helices. Protein Sci 2009; 18:1343-58. [PMID: 19530249 PMCID: PMC2775205 DOI: 10.1002/pro.154] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2009] [Revised: 04/19/2009] [Accepted: 04/20/2009] [Indexed: 12/23/2022]
Abstract
Within 1 or 2 decades, the reputation of membrane-spanning alpha-helices has changed dramatically. Once mostly regarded as dull membrane anchors, transmembrane domains are now recognized as major instigators of protein-protein interaction. These interactions may be of exquisite specificity in mediating assembly of stable membrane protein complexes from cognate subunits. Further, they can be reversible and regulatable by external factors to allow for dynamic changes of protein conformation in biological function. Finally, these helices are increasingly regarded as dynamic domains. These domains can move relative to each other in different functional protein conformations. In addition, small-scale backbone fluctuations may affect their function and their impact on surrounding lipid shells. Elucidating the ways by which these intricate structural features are encoded by the amino acid sequences will be a fascinating subject of research for years to come.
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Affiliation(s)
- Dieter Langosch
- Lehrstuhl Chemie der Biopolymere, Technische Universität München, Weihenstephaner Berg 3, 85354 Freising, Germany.
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36
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Lovell CS, Wise KE, Kim JW, Lillehei PT, Harrison JS, Park C. Thermodynamic approach to enhanced dispersion and physical properties in a carbon nanotube/polypeptide nanocomposite. POLYMER 2009. [DOI: 10.1016/j.polymer.2009.02.016] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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37
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Abstract
The lactose permease of Escherichia coli (LacY) is a highly dynamic membrane transport protein. Crystal structures of wild-type and mutant LacY all exhibit an inward-facing conformation with an open cytoplasmic pathway and a tightly packed periplasmic side, which makes the binding site inaccessible from the outside. However, biochemical and biophysical findings provide strong evidence that occupation of the sugar-binding site leads to an increased probability of opening of a hydrophilic pathway on the periplasmic side and closing of the cytoplasmic cavity. By this means, the sugar-binding site becomes accessible to either side of the membrane in alternating fashion. To extend studies on the relationship between the periplasmic pathway and transport activity, engineered single-Cys replacements in the periplasmic pathway were reacted to completion with thiol reagents, and the effects on transport and sugar binding were tested. Inactivation correlates for the most part with the size of the modifying reagent, although the position of the Cys replacement is also important. However, sugar binding is unaffected. The results suggest that placement of a relatively large moiety in the putative periplasmic cleft of LacY likely prevents closure, an essential step in the transport cycle, without significantly altering access of sugar to the binding site.
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Affiliation(s)
- Yiling Nie
- Department of Physiology, Molecular Biology Institute, University of California, Los Angeles, California 90095, USA
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38
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Abstract
The effect of bulk-phase pH on the apparent affinity (K(d)(app)) of purified wild-type lactose permease (LacY) for sugars was studied. K(d)(app) values were determined by ligand-induced changes in the fluorescence of either of two covalently bound fluorescent reporters positioned away from the sugar-binding site. K(d)(app) for three different galactopyranosides was determined over a pH range from 5.5 to 11. A remarkably high pK(a) of approximately 10.5 was obtained for all sugars. Kinetic data for thiodigalactoside binding measured from pH 6 to 10 show that decreased affinity for sugar at alkaline pH is due specifically to increased reverse rate. A similar effect was also observed with nitrophenylgalactoside by using a direct binding assay. Because affinity for sugar remains constant from pH 5.5 to pH 9.0, it follows that LacY is fully protonated with respect to sugar binding under physiological conditions of pH. The results are consistent with the conclusion that LacY is protonated before sugar binding during lactose/H(+) symport in either direction across the membrane.
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39
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Sequence-specific conformational flexibility of SNARE transmembrane helices probed by hydrogen/deuterium exchange. Biophys J 2008; 95:1326-35. [PMID: 18456822 DOI: 10.1529/biophysj.108.132928] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
SNARE proteins mediate fusion of intracellular eukaryotic membranes and their alpha-helical transmembrane domains are known to contribute to lipid bilayer mixing. Synthetic transmembrane domain peptides were previously shown to mimic the function of SNARE proteins in that they trigger liposome fusion in a sequence-specific fashion. Here, we performed a detailed investigation of the conformational dynamics of the transmembrane helices of the presynaptic SNAREs synaptobrevin II and syntaxin 1a. To this end, we recorded deuterium/hydrogen-exchange kinetics in isotropic solution as well as in the membrane-embedded state. In solution, the exchange kinetics of each peptide can be described by three different classes of amide deuteriums that exchange with different rate constants. These are likely to originate from exchange at different domains of the helices. Interestingly, the rate constants of each class vary with the TMD sequence. Thus, the exchange rate is position-specific and sequence-specific. Further, the rate constants correlate with the previously determined membrane fusogenicities. In membranes, exchange is retarded and a significant proportion of amide hydrogens are protected from exchange. We conclude that the conformational dynamics of SNARE TMD helices is mechanistically linked to their ability to drive lipid mixing.
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40
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Nie Y, Sabetfard FE, Kaback HR. The Cys154-->Gly mutation in LacY causes constitutive opening of the hydrophilic periplasmic pathway. J Mol Biol 2008; 379:695-703. [PMID: 18485365 DOI: 10.1016/j.jmb.2008.04.015] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2008] [Revised: 03/31/2008] [Accepted: 04/07/2008] [Indexed: 11/24/2022]
Abstract
The lactose permease of Escherichia coli (LacY) is a highly dynamic membrane transport protein, while the Cys154-->Gly mutant is crippled conformationally. The mutant binds sugar with high affinity, but catalyzes very little translocation across the membrane. In order to further investigate the defect in the mutant, fluorescent maleimides were used to examine the accessibility/reactivity of single-Cys LacY in right-side-out membrane vesicles. As shown previously, sugar binding induces an increase in reactivity of single-Cys replacements in the tightly packed periplasmic domain of wild-type LacY, while decreased reactivity is observed on the cytoplasmic side. Thus, the predominant population of wild-type LacY in the membrane is in an inward-facing conformation in the absence of sugar, sugar binding induces opening of a hydrophilic pathway on the periplasmic side, and the sugar-binding site is alternatively accessible to either side of the membrane. In striking contrast, the accessibility/reactivity of periplasmic Cys replacements in the Cys154-->Gly background is very high in the absence of sugar, and sugar binding has little or no effect. The observations indicate that an open hydrophilic pathway is present on the periplasmic side of the Cys154-->Gly mutant and that this pathway is unaffected by ligand binding, a conclusion consistent with findings obtained from single-molecule fluorescence and double electron-electron resonance.
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Affiliation(s)
- Yiling Nie
- Department of Physiology, University of California Los Angeles, MacDonald Research Laboratories (Rm 6720), 675 Charles E. Young Drive South, Los Angeles, CA 90095-1662, USA
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41
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Abstract
X-ray crystal structures of lactose permease (LacY) reveal pseudosymmetrically arranged N- and C-terminal six-transmembrane helix bundles surrounding a deep internal cavity open on the cytoplasmic side and completely closed on the periplasmic side. The residues essential for sugar recognition and H(+) translocation are located at the apex of the cavity and are inaccessible from the outside. On the periplasmic side, helices I/II and VII from the N- and C- six helix bundles, respectively, participate in sealing the cavity from the outside. Three paired double-Cys mutants-Ile-40 --> Cys/Asn-245 --> Cys, Thr-45 --> Cys/Asn-245 --> Cys, and Ile-32 --> Cys/Asn-245 --> Cys-located in the interface between helices I/II and VII on the periplasmic side of LacY were constructed. After cross-linking with homobifunctional reagents less than approximately 15 A in length, all three mutants lose the ability to catalyze lactose transport. Strikingly, however, full or partial activity is observed when cross-linking is mediated by flexible reagents greater than approximately 15 A in length. The results provide direct support for the argument that transport via LacY involves opening and closing of a large periplasmic cavity.
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42
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Lehner I, Basting D, Meyer B, Haase W, Manolikas T, Kaiser C, Karas M, Glaubitz C. The Key Residue for Substrate Transport (Glu14) in the EmrE Dimer Is Asymmetric. J Biol Chem 2008; 283:3281-3288. [DOI: 10.1074/jbc.m707899200] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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43
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FTIR spectroscopy of secondary-structure reorientation of melibiose permease modulated by substrate binding. Biophys J 2007; 94:3659-70. [PMID: 18024501 DOI: 10.1529/biophysj.107.115550] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Analysis of infrared polarized absorbance spectra and linear dichroism spectra of reconstituted melibiose permease from Escherichia coli shows that the oriented structures correspond mainly to tilted transmembrane alpha-helices, forming an average angle of approximately 26 degrees with the membrane normal in substrate-free medium. Examination of the deconvoluted linear dichroism spectra in H(2)O and D(2)O makes apparent two populations of alpha-helices differing by their tilt angle (helix types I and II). Moreover, the average helical tilt angle significantly varies upon substrate binding: it is increased upon Na(+) binding, whereas it decreases upon subsequent melibiose binding in the presence of Na(+). In contrast, melibiose binding in the presence of H(+) causes virtually no change in the average tilt angle. The data also suggest that the two helix populations change their tilting and H/D exchange level in different ways depending on the bound substrate(s). Notably, cation binding essentially influences type I helices, whereas melibiose binding modifies the tilting of both helix populations.
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44
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Smirnova I, Kasho V, Choe JY, Altenbach C, Hubbell WL, Kaback HR. Sugar binding induces an outward facing conformation of LacY. Proc Natl Acad Sci U S A 2007; 104:16504-9. [PMID: 17925435 PMCID: PMC2034228 DOI: 10.1073/pnas.0708258104] [Citation(s) in RCA: 153] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2007] [Indexed: 11/18/2022] Open
Abstract
According to x-ray structure, the lactose permease (LacY) is a monomer organized into N- and C-terminal six-helix bundles that form a deep internal cavity open on the cytoplasmic side with a single sugar-binding site at the apex. The periplasmic side of the molecule is closed. During sugar/H(+) symport, a cavity facing the periplasmic side is thought to open with closure of the inward-facing cytoplasmic cavity so that the sugar-binding site is alternately accessible to either face of the membrane. Double electron-electron resonance (DEER) is used here to measure interhelical distance changes induced by sugar binding to LacY. Nitroxide-labeled paired-Cys replacements were constructed at the ends of transmembrane helices on the cytoplasmic or periplasmic sides of wild-type LacY and in the conformationally restricted mutant Cys-154-->Gly. Distances were then determined in the presence of galactosidic or nongalactosidic sugars. Strikingly, specific binding causes conformational rearrangement on both sides of the molecule. On the cytoplasmic side, each of six nitroxide-labeled pairs exhibits decreased interspin distances ranging from 4 to 21 A. Conversely, on the periplasmic side, each of three spin-labeled pairs shows increased distances ranging from 4 to 14 A. Thus, the inward-facing cytoplasmic cavity closes, and a cleft opens on the tightly packed periplasmic side. In the Cys-154-->Gly mutant, sugar-induced closing is observed on the cytoplasmic face, but little or no change occurs on periplasmic side. The DEER measurements in conjunction with molecular modeling based on the x-ray structure provide strong support for the alternative access model and reveal a structure for the outward-facing conformer of LacY.
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Affiliation(s)
| | | | | | - Christian Altenbach
- Jules Stein Eye Institute, and
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095
| | - Wayne L. Hubbell
- Jules Stein Eye Institute, and
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095
| | - H. Ronald Kaback
- *Department of Physiology
- Department of Microbiology, Immunology, and Molecular Genetics
- Molecular Biology Institute
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45
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Guan L, Mirza O, Verner G, Iwata S, Kaback HR. Structural determination of wild-type lactose permease. Proc Natl Acad Sci U S A 2007; 104:15294-8. [PMID: 17881559 PMCID: PMC2000551 DOI: 10.1073/pnas.0707688104] [Citation(s) in RCA: 196] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Here we describe an x-ray structure of wild-type lactose permease (LacY) from Escherichia coli determined by manipulating phospholipid content during crystallization. The structure exhibits the same global fold as the previous x-ray structures of a mutant that binds sugar but cannot catalyze translocation across the membrane. LacY is organized into two six-helix bundles with twofold pseudosymmetry separated by a large interior hydrophilic cavity open only to the cytoplasmic side and containing the side chains important for sugar and H(+) binding. To initiate transport, binding of sugar and/or an H(+) electrochemical gradient increases the probability of opening on the periplasmic side. Because the inward-facing conformation represents the lowest free-energy state, the rate-limiting step for transport may be the conformational change leading to the outward-facing conformation.
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Affiliation(s)
- Lan Guan
- *Department of Physiology and Department of Microbiology, Immunology, and Molecular Genetics, Molecular Biology Institute, University of California, Los Angeles, CA 90095-1662
| | - Osman Mirza
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark
- Division of Molecular Biosciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Gillian Verner
- *Department of Physiology and Department of Microbiology, Immunology, and Molecular Genetics, Molecular Biology Institute, University of California, Los Angeles, CA 90095-1662
| | - So Iwata
- Division of Molecular Biosciences, Imperial College London, London SW7 2AZ, United Kingdom
- Exploratory Research for Advanced Technology Human Receptor Crystallography Project, Kawasaki, 210-0855 Kanagawa, Japan; and
- RIKEN Genomics Sciences Center, 1-7-22 Suchiro-cho, Tsumi, Yokohama 230-0045, Japan
| | - H. Ronald Kaback
- *Department of Physiology and Department of Microbiology, Immunology, and Molecular Genetics, Molecular Biology Institute, University of California, Los Angeles, CA 90095-1662
- To whom correspondence should be addressed. E-mail:
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46
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Barth A. Infrared spectroscopy of proteins. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2007; 1767:1073-101. [PMID: 17692815 DOI: 10.1016/j.bbabio.2007.06.004] [Citation(s) in RCA: 2800] [Impact Index Per Article: 164.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/05/2007] [Revised: 06/18/2007] [Accepted: 06/19/2007] [Indexed: 12/12/2022]
Abstract
This review discusses the application of infrared spectroscopy to the study of proteins. The focus is on the mid-infrared spectral region and the study of protein reactions by reaction-induced infrared difference spectroscopy.
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Affiliation(s)
- Andreas Barth
- Department of Biochemistry and Biophysics, The Arrhenius Laboratories for Natural Sciences, Stockholm University, S-106 91 Stockholm, Sweden.
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47
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Holyoake J, Sansom MSP. Conformational Change in an MFS Protein: MD Simulations of LacY. Structure 2007; 15:873-84. [PMID: 17637346 DOI: 10.1016/j.str.2007.06.004] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2007] [Revised: 06/07/2007] [Accepted: 06/07/2007] [Indexed: 11/30/2022]
Abstract
Molecular dynamics simulations of lactose permease (LacY) in a phospholipid bilayer reveal the conformational dynamics of the protein. In inhibitor-bound simulations (i.e., those closest to the X-ray structure) the protein was stable, showing little conformational change over a 50 ns timescale. Movement of the bound inhibitor, TDG, to an alternative binding mode was observed, so that it interacted predominantly with the N-terminal domain and with residue E269 from the C-terminal domain. In multiple ligand-free simulations, a degree of domain closure occurred. This switched LacY to a state with a central cavity closed at both the intracellular and periplasmic ends. This may resemble a possible intermediate in the transport mechanism. Domain closure occurs by a combination of rigid-body movements of domains and of intradomain motions of helices, especially TM4, TM5, TM10, and TM11. A degree of intrahelix flexibility appears to be important in the conformational change.
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Affiliation(s)
- John Holyoake
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
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48
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Nie Y, Smirnova I, Kasho V, Kaback HR. Energetics of ligand-induced conformational flexibility in the lactose permease of Escherichia coli. J Biol Chem 2006; 281:35779-84. [PMID: 17003033 PMCID: PMC2793331 DOI: 10.1074/jbc.m607232200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Isothermal titration calorimetry has been applied to characterize the thermodynamics of ligand binding to wild-type lactose permease (LacY) and a mutant (C154G) that strongly favors an inward facing conformation. The affinity of wild-type or mutant LacY for ligand and the change in free energy (DeltaG) upon binding are similar. However, with the wild type, the change in free energy upon binding is due primarily to an increase in the entropic free energy component (TDeltaS), whereas in marked contrast, an increase in enthalpy (DeltaH) is responsible for DeltaG in the mutant. Thus, wild-type LacY behaves as if there are multiple ligand-bound conformational states, whereas the mutant is severely restricted. The findings also indicate that the structure of the mutant represents a conformational intermediate in the overall transport cycle.
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Affiliation(s)
| | | | | | - H. Ronald Kaback
- To whom correspondence should be addressed: MacDonald Research Laboratories (Rm. 6720), 675 Charles E. Young Dr. South, UCLA, Los Angeles, CA 90095-1662. Tel.: 310-206-5053; Fax: 310-206-8623;
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49
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Lomize AL, Pogozheva ID, Lomize MA, Mosberg HI. Positioning of proteins in membranes: a computational approach. Protein Sci 2006; 15:1318-33. [PMID: 16731967 PMCID: PMC2242528 DOI: 10.1110/ps.062126106] [Citation(s) in RCA: 158] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
A new computational approach has been developed to determine the spatial arrangement of proteins in membranes by minimizing their transfer energies from water to the lipid bilayer. The membrane hydrocarbon core was approximated as a planar slab of adjustable thickness with decadiene-like interior and interfacial polarity profiles derived from published EPR studies. Applicability and accuracy of the method was verified for a set of 24 transmembrane proteins whose orientations in membranes have been studied by spin-labeling, chemical modification, fluorescence, ATR FTIR, NMR, cryo-microscopy, and neutron diffraction. Subsequently, the optimal rotational and translational positions were calculated for 109 transmembrane, five integral monotopic and 27 peripheral protein complexes with known 3D structures. This method can reliably distinguish transmembrane and integral monotopic proteins from water-soluble proteins based on their transfer energies and membrane penetration depths. The accuracies of calculated hydrophobic thicknesses and tilt angles were approximately 1 A and 2 degrees, respectively, judging from their deviations in different crystal forms of the same proteins. The hydrophobic thicknesses of transmembrane proteins ranged from 21.1 to 43.8 A depending on the type of biological membrane, while their tilt angles with respect to the bilayer normal varied from zero in symmetric complexes to 26 degrees in asymmetric structures. Calculated hydrophobic boundaries of proteins are located approximately 5 A lower than lipid phosphates and correspond to the zero membrane depth parameter of spin-labeled residues. Coordinates of all studied proteins with their membrane boundaries can be found in the Orientations of Proteins in Membranes (OPM) database:http://opm.phar.umich.edu/.
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Affiliation(s)
- Andrei L Lomize
- College of Pharmacy, University of Michigan, Ann Arbor, Michigan 48109-1065, USA.
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50
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Abstract
An X-ray structure of the lactose permease of Escherichia coli (LacY) in an inward-facing conformation has been solved. LacY contains N- and C-terminal domains, each with six transmembrane helices, positioned pseudosymmetrically. Ligand is bound at the apex of a hydrophilic cavity in the approximate middle of the molecule. Residues involved in substrate binding and H+ translocation are aligned parallel to the membrane at the same level and may be exposed to a water-filled cavity in both the inward- and outward-facing conformations, thereby allowing both sugar and H+ release directly into either cavity. These structural features may explain why LacY catalyzes galactoside/H+ symport in both directions utilizing the same residues. A working model for the mechanism is presented that involves alternating access of both the sugar- and H+-binding sites to either side of the membrane.
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Affiliation(s)
- Lan Guan
- Department of Physiology, University of California, Los Angeles, California 90095-1662
| | - H. Ronald Kaback
- Department of Physiology, University of California, Los Angeles, California 90095-1662
- Department of Microbiology, Immunology & Molecular Genetics, University of California, Los Angeles, California 90095-1662
- Department of Molecular Biology Institute, University of California, Los Angeles, California 90095-1662
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