1
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Sinha Roy A, Marohn JA, Freed JH. An analysis of double-quantum coherence ESR in an N-spin system: Analytical expressions and predictions. J Chem Phys 2024; 160:134105. [PMID: 38557852 PMCID: PMC11087869 DOI: 10.1063/5.0200054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2024] [Accepted: 03/12/2024] [Indexed: 04/04/2024] Open
Abstract
Electron spin resonance pulsed dipolar spectroscopy (PDS) has become popular in protein 3D structure analysis. PDS studies yield distance distributions between a pair or multiple pairs of spin probes attached to protein molecules, which can be used directly in structural studies or as constraints in theoretical predictions. Double-quantum coherence (DQC) is a highly sensitive and accurate PDS technique to study protein structures in the solid state and under physiologically relevant conditions. In this work, we have derived analytical expressions for the DQC signal for a system with N-dipolar coupled spin-1/2 particles in the solid state. The expressions are integrated over the relevant spatial parameters to obtain closed form DQC signal expressions. These expressions contain the concentration-dependent "instantaneous diffusion" and the background signal. For micromolar and lower concentrations, these effects are negligible. An approximate analysis is provided for cases of finite pulses. The expressions obtained in this work should improve the analysis of DQC experimental data significantly, and the analytical approach could be extended easily to a wide range of magnetic resonance phenomena.
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Affiliation(s)
| | - John A. Marohn
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, USA
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2
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Wright NJ, Zhang F, Suo Y, Kong L, Yin Y, Fedor JG, Sharma K, Borgnia MJ, Im W, Lee SY. Antiviral drug recognition and elevator-type transport motions of CNT3. Nat Chem Biol 2024:10.1038/s41589-024-01559-8. [PMID: 38418906 DOI: 10.1038/s41589-024-01559-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Accepted: 01/22/2024] [Indexed: 03/02/2024]
Abstract
Nucleoside analogs have broad clinical utility as antiviral drugs. Key to their systemic distribution and cellular entry are human nucleoside transporters. Here, we establish that the human concentrative nucleoside transporter 3 (CNT3) interacts with antiviral drugs used in the treatment of coronavirus infections. We report high-resolution single-particle cryo-electron microscopy structures of bovine CNT3 complexed with antiviral nucleosides N4-hydroxycytidine, PSI-6206, GS-441524 and ribavirin, all in inward-facing states. Notably, we found that the orally bioavailable antiviral molnupiravir arrests CNT3 in four distinct conformations, allowing us to capture cryo-electron microscopy structures of drug-loaded outward-facing and drug-loaded intermediate states. Our studies uncover the conformational trajectory of CNT3 during membrane transport of a nucleoside analog antiviral drug, yield new insights into the role of interactions between the transport and the scaffold domains in elevator-like domain movements during drug translocation, and provide insights into the design of nucleoside analog antiviral prodrugs with improved oral bioavailability.
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Affiliation(s)
- Nicholas J Wright
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Feng Zhang
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Yang Suo
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Lingyang Kong
- Departments of Biological Sciences, Chemistry, and Bioengineering, Lehigh University, Bethlehem, PA, USA
| | - Ying Yin
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Justin G Fedor
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Kedar Sharma
- Department of Health and Human Services, Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, Durham, NC, USA
| | - Mario J Borgnia
- Department of Health and Human Services, Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, Durham, NC, USA
| | - Wonpil Im
- Departments of Biological Sciences, Chemistry, and Bioengineering, Lehigh University, Bethlehem, PA, USA
| | - Seok-Yong Lee
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA.
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3
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Sanders G, Borbat PP, Georgieva ER. A comparative study of influenza A M2 protein conformations in DOPC/DOPS liposomes and in native E. coli membranes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.08.574681. [PMID: 38260371 PMCID: PMC10802500 DOI: 10.1101/2024.01.08.574681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
We compared the conformations of the transmembrane domain (TMD) of influenza A M2 (IAM2) protein reconstituted at pH 7.4 in DOPC/DOPS bilayers to those in isolated E. coli membranes, having preserved its native proteins and lipids. IAM2 is a single-pass transmembrane protein known to assemble into homo-tetrameric proton channel. To represent this channel, we made a construct containing the IAM2's TMD region flanked by the juxtamembrane residues. The single cysteine substitute, L43C, of leucine located in the bilayer polar region was paramagnetically tagged with a methanethiosulfonate nitroxide label for the ESR (electron spin resonance) study. We compared the conformations of the spin-labeled IAM2 residing in DOPC/DOPS and native E. coli membranes using continuous-wave (CW) ESR and double electron-electron resonance (DEER) spectroscopy. The total protein-to-lipid molar ratio spanned the range from 1:230 to 1:10,400⩦ The CW ESR spectra corresponded to a nearly rigid limit spin label dynamics in both environments. In all cases, the DEER data were reconstructed into the distance distributions showing well-resolved peaks at 1.68 nm and 2.37 nm. The peak distance ratio was 1.41±0.2 and the amplitude ratio was 2:1. This is what one expects from four nitroxide spin-labels located at the corners of a square, indicative of an axially symmetric tetramer. Distance modeling of DEER data with molecular modeling software applied to the NMR molecular structures (PDB: 2L0J) confirmed the symmetry and closed state of the C-terminal exit pore of the IAM2 tetramer in agreement with the NMR model. Thus, we can conclude that IAM2 TMD has similar conformations in model and native E. coli membranes of comparable thickness and fluidity, notwithstanding the complexity of the E. coli membranes caused by their lipid diversity and the abundance of integral and peripheral membrane proteins.
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Affiliation(s)
- Griffin Sanders
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX, 79409
| | - Peter P. Borbat
- Department of Chemistry and Chemical Biology and ACERT, Cornell University, Ithaca NY 14853
| | - Elka R. Georgieva
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX, 79409
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4
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Majeed S, Dang L, Islam MM, Ishola O, Borbat PP, Ludtke SJ, Georgieva ER. HIV-1 Vpu protein forms stable oligomers in aqueous solution via its transmembrane domain self-association. Sci Rep 2023; 13:14691. [PMID: 37673923 PMCID: PMC10483038 DOI: 10.1038/s41598-023-41873-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Accepted: 09/01/2023] [Indexed: 09/08/2023] Open
Abstract
We report our findings on the assembly of the HIV-1 protein Vpu into soluble oligomers. Vpu is a key HIV-1 protein. It has been considered exclusively a single-pass membrane protein. Previous observations show that this protein forms stable oligomers in aqueous solution, but details about these oligomers still remain obscure. This is an interesting and rather unique observation, as the number of proteins transitioning between soluble and membrane embedded states is limited. In this study we made use of protein engineering, size exclusion chromatography, cryoEM and electron paramagnetic resonance (EPR) spectroscopy to better elucidate the nature of the soluble oligomers. We found that Vpu oligomerizes via its N-terminal transmembrane domain (TM). CryoEM suggests that the oligomeric state most likely is a hexamer/heptamer equilibrium. Both cryoEM and EPR suggest that, within the oligomer, the distal C-terminal region of Vpu is highly flexible. Our observations are consistent with both the concept of specific interactions among TM helices or the core of the oligomers being stabilized by hydrophobic forces. While this study does not resolve all of the questions about Vpu oligomers or their functional role in HIV-1 it provides new fundamental information about the size and nature of the oligomeric interactions.
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Affiliation(s)
- Saman Majeed
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX, 79409, USA
| | - Lan Dang
- Graduate Program in Quantitative and Computational Biosciences, Graduate School of Biomedical Sciences at Baylor College of Medicine, Houston, TX, USA
| | - Md Majharul Islam
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX, 79409, USA
| | - Olamide Ishola
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX, 79409, USA
| | - Peter P Borbat
- Department of Chemistry and Chemical Biology and ACERT, Cornell University, Ithaca, NY, 14853, USA
| | - Steven J Ludtke
- Department of Biochemistry and Molecular Pharmacology, Baylor College of Medicine, Houston, TX, 77030, USA.
| | - Elka R Georgieva
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX, 79409, USA.
- Center for Membrane Protein Research, TTU Health Science Center, Lubbock, TX, 79430, USA.
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5
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Haysom SF, Machin J, Whitehouse JM, Horne JE, Fenn K, Ma Y, El Mkami H, Böhringer N, Schäberle TF, Ranson NA, Radford SE, Pliotas C. Darobactin B Stabilises a Lateral-Closed Conformation of the BAM Complex in E. coli Cells. ANGEWANDTE CHEMIE (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2023; 135:e202218783. [PMID: 38515502 PMCID: PMC10952338 DOI: 10.1002/ange.202218783] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Indexed: 03/23/2024]
Abstract
The β-barrel assembly machinery (BAM complex) is essential for outer membrane protein (OMP) folding in Gram-negative bacteria, and represents a promising antimicrobial target. Several conformational states of BAM have been reported, but all have been obtained under conditions which lack the unique features and complexity of the outer membrane (OM). Here, we use Pulsed Electron-Electron Double Resonance (PELDOR, or DEER) spectroscopy distance measurements to interrogate the conformational ensemble of the BAM complex in E. coli cells. We show that BAM adopts a broad ensemble of conformations in the OM, while in the presence of the antibiotic darobactin B (DAR-B), BAM's conformational equilibrium shifts to a restricted ensemble consistent with the lateral closed state. Our in-cell PELDOR findings are supported by new cryoEM structures of BAM in the presence and absence of DAR-B. This work demonstrates the utility of PELDOR to map conformational changes in BAM within its native cellular environment.
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Affiliation(s)
- Samuel F. Haysom
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - Jonathan Machin
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - James M. Whitehouse
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - Jim E. Horne
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - Katherine Fenn
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - Yue Ma
- Astbury Centre for Structural Molecular BiologySchool of Biomedical SciencesUniversity of LeedsLeedsLS2 9JTUK
- School of Biological Sciences, Faculty of Biology, Medicine and HealthManchester Academic and Health Science CentreThe University of ManchesterManchesterM13 9PTUK
- Manchester Institute of BiotechnologyThe University of ManchesterManchesterM1 7DNUK
| | - Hassane El Mkami
- School of Physics and AstronomyUniversity of St. AndrewsSt. AndrewsKY16 9SSUK
| | - Nils Böhringer
- Institute for Insect BiotechnologyNatural Product ResearchJustus-Liebig-University GiessenOhlebergsweg 1235392GiessenGermany
- German Center for Infection Research (DZIF)Partner Site Giessen-Marburg-LangenOhlebergsweg 1235392GiessenGermany
| | - Till F. Schäberle
- Institute for Insect BiotechnologyNatural Product ResearchJustus-Liebig-University GiessenOhlebergsweg 1235392GiessenGermany
- German Center for Infection Research (DZIF)Partner Site Giessen-Marburg-LangenOhlebergsweg 1235392GiessenGermany
- Natural Product DepartmentFraunhofer-Institute for Molecular Biology and Applied Ecology (IME)Ohlebergsweg 1235392GiessenGermany
| | - Neil A. Ranson
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - Sheena E. Radford
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - Christos Pliotas
- Astbury Centre for Structural Molecular BiologySchool of Biomedical SciencesUniversity of LeedsLeedsLS2 9JTUK
- School of Biological Sciences, Faculty of Biology, Medicine and HealthManchester Academic and Health Science CentreThe University of ManchesterManchesterM13 9PTUK
- Manchester Institute of BiotechnologyThe University of ManchesterManchesterM1 7DNUK
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6
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Haysom SF, Machin J, Whitehouse JM, Horne JE, Fenn K, Ma Y, El Mkami H, Böhringer N, Schäberle TF, Ranson NA, Radford SE, Pliotas C. Darobactin B Stabilises a Lateral-Closed Conformation of the BAM Complex in E. coli Cells. Angew Chem Int Ed Engl 2023; 62:e202218783. [PMID: 37162386 PMCID: PMC10952311 DOI: 10.1002/anie.202218783] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Revised: 04/26/2023] [Accepted: 05/09/2023] [Indexed: 05/11/2023]
Abstract
The β-barrel assembly machinery (BAM complex) is essential for outer membrane protein (OMP) folding in Gram-negative bacteria, and represents a promising antimicrobial target. Several conformational states of BAM have been reported, but all have been obtained under conditions which lack the unique features and complexity of the outer membrane (OM). Here, we use Pulsed Electron-Electron Double Resonance (PELDOR, or DEER) spectroscopy distance measurements to interrogate the conformational ensemble of the BAM complex in E. coli cells. We show that BAM adopts a broad ensemble of conformations in the OM, while in the presence of the antibiotic darobactin B (DAR-B), BAM's conformational equilibrium shifts to a restricted ensemble consistent with the lateral closed state. Our in-cell PELDOR findings are supported by new cryoEM structures of BAM in the presence and absence of DAR-B. This work demonstrates the utility of PELDOR to map conformational changes in BAM within its native cellular environment.
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Affiliation(s)
- Samuel F. Haysom
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - Jonathan Machin
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - James M. Whitehouse
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - Jim E. Horne
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - Katherine Fenn
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - Yue Ma
- Astbury Centre for Structural Molecular BiologySchool of Biomedical SciencesUniversity of LeedsLeedsLS2 9JTUK
- School of Biological Sciences, Faculty of Biology, Medicine and HealthManchester Academic and Health Science CentreThe University of ManchesterManchesterM13 9PTUK
- Manchester Institute of BiotechnologyThe University of ManchesterManchesterM1 7DNUK
| | - Hassane El Mkami
- School of Physics and AstronomyUniversity of St. AndrewsSt. AndrewsKY16 9SSUK
| | - Nils Böhringer
- Institute for Insect BiotechnologyNatural Product ResearchJustus-Liebig-University GiessenOhlebergsweg 1235392GiessenGermany
- German Center for Infection Research (DZIF)Partner Site Giessen-Marburg-LangenOhlebergsweg 1235392GiessenGermany
| | - Till F. Schäberle
- Institute for Insect BiotechnologyNatural Product ResearchJustus-Liebig-University GiessenOhlebergsweg 1235392GiessenGermany
- German Center for Infection Research (DZIF)Partner Site Giessen-Marburg-LangenOhlebergsweg 1235392GiessenGermany
- Natural Product DepartmentFraunhofer-Institute for Molecular Biology and Applied Ecology (IME)Ohlebergsweg 1235392GiessenGermany
| | - Neil A. Ranson
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - Sheena E. Radford
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - Christos Pliotas
- Astbury Centre for Structural Molecular BiologySchool of Biomedical SciencesUniversity of LeedsLeedsLS2 9JTUK
- School of Biological Sciences, Faculty of Biology, Medicine and HealthManchester Academic and Health Science CentreThe University of ManchesterManchesterM13 9PTUK
- Manchester Institute of BiotechnologyThe University of ManchesterManchesterM1 7DNUK
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7
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Majeed S, Dang L, Islam MM, Ishola O, Borbat PP, Ludtke SJ, Georgieva ER. HIV-1 Vpu protein forms stable oligomers in aqueous solution via its transmembrane domain self-association. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.08.539839. [PMID: 37214796 PMCID: PMC10197565 DOI: 10.1101/2023.05.08.539839] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We report our findings on the assembly of the HIV-1 protein Vpu into soluble oligomers. Vpu is a key to HIV-1 protein. It has been considered exclusively a single-pass membrane protein. However, we revealed that this protein forms stable oligomers in aqueous solution, which is an interesting and rather unique observation, as the number of proteins transitioning between soluble and membrane embedded states is limited. Therefore, we undertook a study to characterize these oligomers by utilizing protein engineering, size exclusion chromatography, cryoEM and electron paramagnetic resonance (EPR) spectroscopy. We found that Vpu oligomerizes via its N-terminal transmembrane domain (TM). CryoEM analyses suggest that the oligomeric state most likely is a hexamer or hexamer-to-heptamer equilibrium. Both cryoEM and EPR suggest that, within the oligomer, the distant C-terminal region of Vpu is highly flexible. To the best of our knowledge, this is the first comprehensive study on soluble Vpu. We propose that these oligomers are stabilized via possibly hydrophobic interactions between Vpu TMs. Our findings contribute valuable information about this protein properties and about protein supramolecular complexes formation. The acquired knowledge could be further used in protein engineering, and could also help to uncover possible physiological function of these Vpu oligomers.
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Affiliation(s)
- Saman Majeed
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| | - Lan Dang
- Graduate Program in Quantitative and Computational Biosciences, Graduate School of Biomedical Sciences at Baylor College of Medicine, Houston, Texas, USA
| | - Md Majharul Islam
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| | - Olamide Ishola
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| | - Peter P. Borbat
- Department of Chemistry and Chemical Biology and ACERT, Cornell University, Ithaca, NY 14853, USA
| | - Steven J. Ludtke
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Elka R. Georgieva
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
- Center for Membrane Protein Research, TTU Health Science Center, Lubbock, TX 79430, USA
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8
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Majeed S, Adetuyi O, Borbat PP, Majharul Islam M, Ishola O, Zhao B, Georgieva ER. Insights into the oligomeric structure of the HIV-1 Vpu protein. J Struct Biol 2023; 215:107943. [PMID: 36796461 PMCID: PMC10257199 DOI: 10.1016/j.jsb.2023.107943] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2022] [Revised: 02/10/2023] [Accepted: 02/11/2023] [Indexed: 02/16/2023]
Abstract
The HIV-1-encoded protein Vpu forms an oligomeric ion channel/pore in membranes and interacts with host proteins to support the virus lifecycle. However, Vpu molecular mechanisms are currently not well understood. Here, we report on the Vpu oligomeric organization under membrane and aqueous conditions and provide insights into how the Vpu environment affects the oligomer formation. For these studies, we designed a maltose-binding protein (MBP)-Vpu chimera protein and produced it in E. coli in soluble form. We analyzed this protein using analytical size-exclusion chromatography (SEC), negative staining electron microscopy (nsEM), and electron paramagnetic resonance (EPR) spectroscopy. Surprisingly, we found that MBP-Vpu formed stable oligomers in solution, seemingly driven by Vpu transmembrane domain self-association. A coarse modeling of nsEM data as well as SEC and EPR data suggests that these oligomers most likely are pentamers, similar to what was reported regarding membrane-bound Vpu. We also noticed reduced MBP-Vpu oligomer stability upon reconstitution of the protein in β-DDM detergent and mixtures of lyso-PC/PG or DHPC/DHPG. In these cases, we observed greater oligomer heterogeneity, with MBP-Vpu oligomeric order generally lower than in solution; however, larger oligomers were also present. Notably, we found that in lyso-PC/PG, above a certain protein concentration, MBP-Vpu assembles into extended structures, which had not been reported for Vpu. Therefore, we captured various Vpu oligomeric forms, which can shed light on Vpu quaternary organization. Our findings could be useful in understanding Vpu organization and function in cellular membranes and could provide information regarding the biophysical properties of single-pass transmembrane proteins.
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Affiliation(s)
- Saman Majeed
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, United States
| | - Oluwatosin Adetuyi
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, United States
| | - Peter P Borbat
- Department of Chemistry and Chemical Biology and ACERT, Cornell University, Ithaca, NY 14853, United States
| | - Md Majharul Islam
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, United States
| | - Olamide Ishola
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, United States
| | - Bo Zhao
- College of Arts & Sciences Microscopy (CASM), Texas Tech University, Lubbock, TX 79409, United States
| | - Elka R Georgieva
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, United States.
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9
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Lane BJ, Wang B, Ma Y, Calabrese AN, El Mkami H, Pliotas C. HDX-guided EPR spectroscopy to interrogate membrane protein dynamics. STAR Protoc 2022; 3:101562. [PMID: 35874470 PMCID: PMC9304679 DOI: 10.1016/j.xpro.2022.101562] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Solvent accessibilities of and distances between protein residues measured by pulsed-EPR approaches provide high-resolution information on dynamic protein motions. We describe protocols for the purification and site-directed spin labeling of integral membrane proteins. In our protocol, peptide-level HDX-MS is used as a precursor to guide single-residue resolution ESEEM accessibility measurements and spin labeling strategies for EPR applications. Exploiting the pentameric MscL channel as a model, we discuss the use of cwEPR, DEER/PELDOR, and ESEEM spectroscopies to interrogate membrane protein dynamics. For complete details on the use and execution of this protocol, please refer to Wang et al. (2022). Protocols for an integrated EPR-based approach to study membrane protein dynamics Instructions for the sample preparation of spin-labeled membrane proteins Used HDX-MS as a precursor to guide spin labeling strategies for EPR methods Probed solvent accessibility at the single-residue level by ESEEM
Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.
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10
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Sauer DB, Marden JJ, Sudar JC, Song J, Mulligan C, Wang DN. Structural basis of ion - substrate coupling in the Na +-dependent dicarboxylate transporter VcINDY. Nat Commun 2022; 13:2644. [PMID: 35551191 PMCID: PMC9098524 DOI: 10.1038/s41467-022-30406-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Accepted: 04/28/2022] [Indexed: 11/21/2022] Open
Abstract
The Na+-dependent dicarboxylate transporter from Vibrio cholerae (VcINDY) is a prototype for the divalent anion sodium symporter (DASS) family. While the utilization of an electrochemical Na+ gradient to power substrate transport is well established for VcINDY, the structural basis of this coupling between sodium and substrate binding is not currently understood. Here, using a combination of cryo-EM structure determination, succinate binding and site-directed cysteine alkylation assays, we demonstrate that the VcINDY protein couples sodium- and substrate-binding via a previously unseen cooperative mechanism by conformational selection. In the absence of sodium, substrate binding is abolished, with the succinate binding regions exhibiting increased flexibility, including HPinb, TM10b and the substrate clamshell motifs. Upon sodium binding, these regions become structurally ordered and create a proper binding site for the substrate. Taken together, these results provide strong evidence that VcINDY's conformational selection mechanism is a result of the sodium-dependent formation of the substrate binding site.
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Affiliation(s)
- David B Sauer
- Department of Cell Biology, New York University School of Medicine, New York, NY, 10016, USA
- Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY, 10016, USA
- Centre for Medicines Discovery, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Jennifer J Marden
- Department of Cell Biology, New York University School of Medicine, New York, NY, 10016, USA
- Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY, 10016, USA
| | - Joseph C Sudar
- Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY, 10016, USA
| | - Jinmei Song
- Department of Cell Biology, New York University School of Medicine, New York, NY, 10016, USA
- Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY, 10016, USA
| | | | - Da-Neng Wang
- Department of Cell Biology, New York University School of Medicine, New York, NY, 10016, USA.
- Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY, 10016, USA.
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11
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Distinct roles of the Na + binding sites in the allosteric coupling mechanism of the glutamate transporter homolog, Glt Ph. Proc Natl Acad Sci U S A 2022; 119:e2121653119. [PMID: 35507872 DOI: 10.1073/pnas.2121653119] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
SignificanceGlutamate transporters harness ionic gradients present across the membrane for the rapid removal of glutamate from the synaptic space. Normal function of glutamate transporters is required for efficient synaptic transmission and preventing excitotoxicity. Central to the transport mechanism is the coupled binding of Na+ and the substrate. While structural studies have identified the Na+ and the substrate binding sites, the mechanism by which Na+ and substrate binding is coupled is not known. In this study, we developed assays to monitor Na+ binding and to track key conformational changes in GltPh, an archaeal homolog of glutamate transporters. We use these assays along with previously developed assays to describe the specific roles of the Na+ sites in the coupling mechanism.
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12
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Reddy KD, Ciftci D, Scopelliti AJ, Boudker O. The archaeal glutamate transporter homologue GltPh shows heterogeneous substrate binding. J Gen Physiol 2022; 154:e202213131. [PMID: 35452090 PMCID: PMC9044058 DOI: 10.1085/jgp.202213131] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Accepted: 03/10/2022] [Indexed: 12/31/2022] Open
Abstract
Integral membrane glutamate transporters couple the concentrative substrate transport to ion gradients. There is a wealth of structural and mechanistic information about this protein family. Recent studies of an archaeal homologue, GltPh, revealed transport rate heterogeneity, which is inconsistent with simple kinetic models; however, its structural and mechanistic determinants remain undefined. Here, we demonstrate that in a mutant GltPh, which exclusively populates the outward-facing state, at least two substates coexist in slow equilibrium, binding the substrate with different apparent affinities. Wild type GltPh shows similar binding properties, and modulation of the substate equilibrium correlates with transport rates. The low-affinity substate of the mutant is transient following substrate binding. Consistently, cryo-EM on samples frozen within seconds after substrate addition reveals the presence of structural classes with perturbed helical packing of the extracellular half of the transport domain in regions adjacent to the binding site. By contrast, an equilibrated structure does not show such classes. The structure at 2.2-Å resolution details a pattern of waters in the intracellular half of the domain and resolves classes with subtle differences in the substrate-binding site. We hypothesize that the rigid cytoplasmic half of the domain mediates substrate and ion recognition and coupling, whereas the extracellular labile half sets the affinity and dynamic properties.
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Affiliation(s)
- Krishna D. Reddy
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY
| | - Didar Ciftci
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY
- Tri-Institutional Training Program in Chemical Biology, New York, NY
| | | | - Olga Boudker
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY
- Howard Hughes Medical Institute, Weill Cornell Medicine, New York, NY
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13
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Puthenveetil R, Christenson ET, Vinogradova O. New Horizons in Structural Biology of Membrane Proteins: Experimental Evaluation of the Role of Conformational Dynamics and Intrinsic Flexibility. MEMBRANES 2022; 12:227. [PMID: 35207148 PMCID: PMC8877495 DOI: 10.3390/membranes12020227] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/01/2022] [Revised: 02/13/2022] [Accepted: 02/14/2022] [Indexed: 02/08/2023]
Abstract
A plethora of membrane proteins are found along the cell surface and on the convoluted labyrinth of membranes surrounding organelles. Since the advent of various structural biology techniques, a sub-population of these proteins has become accessible to investigation at near-atomic resolutions. The predominant bona fide methods for structure solution, X-ray crystallography and cryo-EM, provide high resolution in three-dimensional space at the cost of neglecting protein motions through time. Though structures provide various rigid snapshots, only an amorphous mechanistic understanding can be inferred from interpolations between these different static states. In this review, we discuss various techniques that have been utilized in observing dynamic conformational intermediaries that remain elusive from rigid structures. More specifically we discuss the application of structural techniques such as NMR, cryo-EM and X-ray crystallography in studying protein dynamics along with complementation by conformational trapping by specific binders such as antibodies. We finally showcase the strength of various biophysical techniques including FRET, EPR and computational approaches using a multitude of succinct examples from GPCRs, transporters and ion channels.
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Affiliation(s)
- Robbins Puthenveetil
- Section on Structural and Chemical Biology of Membrane Proteins, Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, 35A Convent Dr., Bethesda, MD 20892, USA
| | | | - Olga Vinogradova
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Connecticut, Storrs, CT 06269, USA
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14
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Hustedt EJ, Stein RA, Mchaourab HS. Protein functional dynamics from the rigorous global analysis of DEER data: Conditions, components, and conformations. J Gen Physiol 2021; 153:212643. [PMID: 34529007 PMCID: PMC8449309 DOI: 10.1085/jgp.201711954] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Accepted: 08/30/2021] [Indexed: 01/03/2023] Open
Abstract
The potential of spin labeling to reveal the dynamic dimension of macromolecules has been recognized since the dawn of the methodology in the 1960s. However, it was the development of pulsed electron paramagnetic resonance spectroscopy to detect dipolar coupling between spin labels and the availability of turnkey instrumentation in the 21st century that realized the full promise of spin labeling. Double electron-electron resonance (DEER) spectroscopy has seen widespread applications to channels, transporters, and receptors. In these studies, distance distributions between pairs of spin labels obtained under different biochemical conditions report the conformational states of macromolecules, illuminating the key movements underlying biological function. These experimental studies have spurred the development of methods for the rigorous analysis of DEER spectroscopic data along with methods for integrating these distributions into structural models. In this tutorial, we describe a model-based approach to obtaining a minimum set of components of the distance distribution that correspond to functionally relevant protein conformations with a set of fractional amplitudes that define the equilibrium between these conformations. Importantly, we review and elaborate on the error analysis reflecting the uncertainty in the various parameters, a critical step in rigorous structural interpretation of the spectroscopic data.
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Affiliation(s)
- Eric J Hustedt
- Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
| | - Richard A Stein
- Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
| | - Hassane S Mchaourab
- Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
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15
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Majeed S, Ahmad AB, Sehar U, Georgieva ER. Lipid Membrane Mimetics in Functional and Structural Studies of Integral Membrane Proteins. MEMBRANES 2021; 11:685. [PMID: 34564502 PMCID: PMC8470526 DOI: 10.3390/membranes11090685] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Revised: 08/18/2021] [Accepted: 08/30/2021] [Indexed: 12/12/2022]
Abstract
Integral membrane proteins (IMPs) fulfill important physiological functions by providing cell-environment, cell-cell and virus-host communication; nutrients intake; export of toxic compounds out of cells; and more. However, some IMPs have obliterated functions due to polypeptide mutations, modifications in membrane properties and/or other environmental factors-resulting in damaged binding to ligands and the adoption of non-physiological conformations that prevent the protein from returning to its physiological state. Thus, elucidating IMPs' mechanisms of function and malfunction at the molecular level is important for enhancing our understanding of cell and organism physiology. This understanding also helps pharmaceutical developments for restoring or inhibiting protein activity. To this end, in vitro studies provide invaluable information about IMPs' structure and the relation between structural dynamics and function. Typically, these studies are conducted on transferred from native membranes to membrane-mimicking nano-platforms (membrane mimetics) purified IMPs. Here, we review the most widely used membrane mimetics in structural and functional studies of IMPs. These membrane mimetics are detergents, liposomes, bicelles, nanodiscs/Lipodisqs, amphipols, and lipidic cubic phases. We also discuss the protocols for IMPs reconstitution in membrane mimetics as well as the applicability of these membrane mimetic-IMP complexes in studies via a variety of biochemical, biophysical, and structural biology techniques.
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Affiliation(s)
- Saman Majeed
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| | - Akram Bani Ahmad
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| | - Ujala Sehar
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| | - Elka R Georgieva
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
- Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Science Center, Lubbock, TX 79409, USA
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16
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Kinetic mechanism of Na +-coupled aspartate transport catalyzed by Glt Tk. Commun Biol 2021; 4:751. [PMID: 34140623 PMCID: PMC8211817 DOI: 10.1038/s42003-021-02267-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Accepted: 05/26/2021] [Indexed: 12/18/2022] Open
Abstract
It is well-established that the secondary active transporters GltTk and GltPh catalyze coupled uptake of aspartate and three sodium ions, but insight in the kinetic mechanism of transport is fragmentary. Here, we systematically measured aspartate uptake rates in proteoliposomes containing purified GltTk, and derived the rate equation for a mechanism in which two sodium ions bind before and another after aspartate. Re-analysis of existing data on GltPh using this equation allowed for determination of the turnover number (0.14 s−1), without the need for error-prone protein quantification. To overcome the complication that purified transporters may adopt right-side-out or inside-out membrane orientations upon reconstitution, thereby confounding the kinetic analysis, we employed a rapid method using synthetic nanobodies to inactivate one population. Oppositely oriented GltTk proteins showed the same transport kinetics, consistent with the use of an identical gating element on both sides of the membrane. Our work underlines the value of bona fide transport experiments to reveal mechanistic features of Na+-aspartate symport that cannot be observed in detergent solution. Combined with previous pre-equilibrium binding studies, a full kinetic mechanism of structurally characterized aspartate transporters of the SLC1A family is now emerging. Trinco et al. measure aspartate uptake rates in proteoliposomes containing purified prokaryotic Na+-coupled aspartate transporter GltTk. To overcome limitation of protein orientation, they use synthetic nanobody that blocks transporters from outside and reveal mechanistic features of Na+-aspartate symport that cannot be observed in detergent solution.
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17
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Hung CL, Chang HH, Lee SW, Chiang YW. Stepwise activation of the pro-apoptotic protein Bid at mitochondrial membranes. Cell Death Differ 2021; 28:1910-1925. [PMID: 33462413 PMCID: PMC8184993 DOI: 10.1038/s41418-020-00716-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 12/01/2020] [Accepted: 12/16/2020] [Indexed: 01/30/2023] Open
Abstract
Caspase-8-cleaved Bid (cBid) associates with mitochondria and promotes the activation of BAX, leading to mitochondria outer membrane permeabilization (MOMP) and apoptosis. However, current structural models of cBid are largely based on studies using membrane vesicles and detergent micelles. Here we employ spin-label ESR and site-directed PEGylation methods to identify conformations of cBid at real mitochondrial membranes, revealing stepwise mechanisms in the activation process. Upon the binding of cBid to mitochondria, its structure is reorganized to expose the BH3 domain while leaving the structural integrity only slightly altered. The mitochondria-bound cBid is in association with Mtch2 and it remains in the primed state until interacting with BAX. The interaction subsequently triggers the fragmentation of cBid, causes large conformational changes, and promotes BAX-mediated MOMP. Our results reveal structural differences of cBid between mitochondria and other lipid-like environments and, moreover, highlight the role of the membrane binding in modifying cBid structure and assisting the inactive-to-active transition in function.
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Affiliation(s)
- Chien-Lun Hung
- Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan
| | - Hsin-Ho Chang
- Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan
| | - Su Wei Lee
- Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan
| | - Yun-Wei Chiang
- Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan.
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18
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Probing Structural Dynamics of Membrane Proteins Using Electron Paramagnetic Resonance Spectroscopic Techniques. BIOPHYSICA 2021. [DOI: 10.3390/biophysica1020009] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Membrane proteins are essential for the survival of living organisms. They are involved in important biological functions including transportation of ions and molecules across the cell membrane and triggering the signaling pathways. They are targets of more than half of the modern medical drugs. Despite their biological significance, information about the structural dynamics of membrane proteins is lagging when compared to that of globular proteins. The major challenges with these systems are low expression yields and lack of appropriate solubilizing medium required for biophysical techniques. Electron paramagnetic resonance (EPR) spectroscopy coupled with site directed spin labeling (SDSL) is a rapidly growing powerful biophysical technique that can be used to obtain pertinent structural and dynamic information on membrane proteins. In this brief review, we will focus on the overview of the widely used EPR approaches and their emerging applications to answer structural and conformational dynamics related questions on important membrane protein systems.
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19
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Claxton DP, Jagessar KL, Mchaourab HS. Principles of Alternating Access in Multidrug and Toxin Extrusion (MATE) Transporters. J Mol Biol 2021; 433:166959. [PMID: 33774036 DOI: 10.1016/j.jmb.2021.166959] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2021] [Revised: 03/15/2021] [Accepted: 03/18/2021] [Indexed: 12/18/2022]
Abstract
The multidrug and toxin extrusion (MATE) transporters catalyze active efflux of a broad range of chemically- and structurally-diverse compounds including antimicrobials and chemotherapeutics, thus contributing to multidrug resistance in pathogenic bacteria and cancers. Multiple methodological approaches have been taken to investigate the structural basis of energy transduction and substrate translocation in MATE transporters. Crystal structures representing members from all three MATE subfamilies have been interpreted within the context of an alternating access mechanism that postulates occupation of distinct structural intermediates in a conformational cycle powered by electrochemical ion gradients. Here we review the structural biology of MATE transporters, integrating the crystallographic models with biophysical and computational studies to define the molecular determinants that shape the transport energy landscape. This holistic analysis highlights both shared and disparate structural and functional features within the MATE family, which underpin an emerging theme of mechanistic diversity within the framework of a conserved structural scaffold.
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Affiliation(s)
- Derek P Claxton
- Department of Molecular Physiology and Biophysics, Vanderbilt University, 747 Light Hall, 2215 Garland Avenue, Nashville, TN 37232, USA
| | - Kevin L Jagessar
- Department of Molecular Physiology and Biophysics, Vanderbilt University, 747 Light Hall, 2215 Garland Avenue, Nashville, TN 37232, USA
| | - Hassane S Mchaourab
- Department of Molecular Physiology and Biophysics, Vanderbilt University, 747 Light Hall, 2215 Garland Avenue, Nashville, TN 37232, USA.
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20
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Huysmans GHM, Ciftci D, Wang X, Blanchard SC, Boudker O. The high-energy transition state of the glutamate transporter homologue GltPh. EMBO J 2021; 40:e105415. [PMID: 33185289 PMCID: PMC7780239 DOI: 10.15252/embj.2020105415] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Revised: 09/16/2020] [Accepted: 09/18/2020] [Indexed: 01/03/2023] Open
Abstract
Membrane transporters mediate cellular uptake of nutrients, signaling molecules, and drugs. Their overall mechanisms are often well understood, but the structural features setting their rates are mostly unknown. Earlier single-molecule fluorescence imaging of the archaeal model glutamate transporter homologue GltPh from Pyrococcus horikoshii suggested that the slow conformational transition from the outward- to the inward-facing state, when the bound substrate is translocated from the extracellular to the cytoplasmic side of the membrane, is rate limiting to transport. Here, we provide insight into the structure of the high-energy transition state of GltPh that limits the rate of the substrate translocation process. Using bioinformatics, we identified GltPh gain-of-function mutations in the flexible helical hairpin domain HP2 and applied linear free energy relationship analysis to infer that the transition state structurally resembles the inward-facing conformation. Based on these analyses, we propose an approach to search for allosteric modulators for transporters.
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Affiliation(s)
- Gerard H M Huysmans
- Department of Physiology and BiophysicsWeill Cornell MedicineNew YorkNYUSA
- Mass Spectrometry for Biology Unit, USR 2000CNRSInstitut PasteurParisFrance
| | - Didar Ciftci
- Department of Physiology and BiophysicsWeill Cornell MedicineNew YorkNYUSA
- Tri‐Institutional Training Program in Chemical BiologyNew YorkNYUSA
| | - Xiaoyu Wang
- Department of Physiology and BiophysicsWeill Cornell MedicineNew YorkNYUSA
| | - Scott C Blanchard
- Department of Physiology and BiophysicsWeill Cornell MedicineNew YorkNYUSA
- Tri‐Institutional Training Program in Chemical BiologyNew YorkNYUSA
- St. Jude Children’s Research HospitalMemphisTNUSA
| | - Olga Boudker
- Department of Physiology and BiophysicsWeill Cornell MedicineNew YorkNYUSA
- Tri‐Institutional Training Program in Chemical BiologyNew YorkNYUSA
- Howard Hughes Medical InstituteChevy ChaseMDUSA
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21
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Sampson CDD, Stewart MJ, Mindell JA, Mulligan C. Solvent accessibility changes in a Na +-dependent C 4-dicarboxylate transporter suggest differential substrate effects in a multistep mechanism. J Biol Chem 2020; 295:18524-18538. [PMID: 33087444 PMCID: PMC7939474 DOI: 10.1074/jbc.ra120.013894] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 10/06/2020] [Indexed: 11/06/2022] Open
Abstract
The divalent anion sodium symporter (DASS) family (SLC13) plays critical roles in metabolic homeostasis, influencing many processes, including fatty acid synthesis, insulin resistance, and adiposity. DASS transporters catalyze the Na+-driven concentrative uptake of Krebs cycle intermediates and sulfate into cells; disrupting their function can protect against age-related metabolic diseases and can extend lifespan. An inward-facing crystal structure and an outward-facing model of a bacterial DASS family member, VcINDY from Vibrio cholerae, predict an elevator-like transport mechanism involving a large rigid body movement of the substrate-binding site. How substrate binding influences the conformational state of VcINDY is currently unknown. Here, we probe the interaction between substrate binding and protein conformation by monitoring substrate-induced solvent accessibility changes of broadly distributed positions in VcINDY using a site-specific alkylation strategy. Our findings reveal that accessibility to all positions tested is modulated by the presence of substrates, with the majority becoming less accessible in the presence of saturating concentrations of both Na+ and succinate. We also observe separable effects of Na+ and succinate binding at several positions suggesting distinct effects of the two substrates. Furthermore, accessibility changes to a solely succinate-sensitive position suggests that substrate binding is a low-affinity, ordered process. Mapping these accessibility changes onto the structures of VcINDY suggests that Na+ binding drives the transporter into an as-yet-unidentified conformational state, involving rearrangement of the substrate-binding site-associated re-entrant hairpin loops. These findings provide insight into the mechanism of VcINDY, which is currently the only structurally characterized representative of the entire DASS family.
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Affiliation(s)
- Connor D D Sampson
- School of Biosciences, University of Kent, Canterbury, Kent, United Kingdom
| | - Matthew J Stewart
- School of Biosciences, University of Kent, Canterbury, Kent, United Kingdom
| | - Joseph A Mindell
- Membrane Transport Biophysics Section, Porter Neuroscience Research Center, NINDS, National Institutes of Health, Bethesda, Maryland, USA
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22
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Viewing rare conformations of the β 2 adrenergic receptor with pressure-resolved DEER spectroscopy. Proc Natl Acad Sci U S A 2020; 117:31824-31831. [PMID: 33257561 DOI: 10.1073/pnas.2013904117] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The β2 adrenergic receptor (β2AR) is an archetypal G protein coupled receptor (GPCR). One structural signature of GPCR activation is a large-scale movement (ca. 6 to 14 Å) of transmembrane helix 6 (TM6) to a conformation which binds and activates a cognate G protein. The β2AR exhibits a low level of agonist-independent G protein activation. The structural origin of this basal activity and its suppression by inverse agonists is unknown but could involve a unique receptor conformation that promotes G protein activation. Alternatively, a conformational selection model proposes that a minor population of the canonical active receptor conformation exists in equilibrium with inactive forms, thus giving rise to basal activity of the ligand-free receptor. Previous spin-labeling and fluorescence resonance energy transfer experiments designed to monitor the positional distribution of TM6 did not detect the presence of the active conformation of ligand-free β2AR. Here we employ spin-labeling and pressure-resolved double electron-electron resonance spectroscopy to reveal the presence of a minor population of unliganded receptor, with the signature outward TM6 displacement, in equilibrium with inactive conformations. Binding of inverse agonists suppresses this population. These results provide direct structural evidence in favor of a conformational selection model for basal activity in β2AR and provide a mechanism for inverse agonism. In addition, they emphasize 1) the importance of minor populations in GPCR catalytic function; 2) the use of spin-labeling and variable-pressure electron paramagnetic resonance to reveal them in a membrane protein; and 3) the quantitative evaluation of their thermodynamic properties relative to the inactive forms, including free energy, partial molar volume, and compressibility.
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23
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Georgieva ER. Protein Conformational Dynamics upon Association with the Surfaces of Lipid Membranes and Engineered Nanoparticles: Insights from Electron Paramagnetic Resonance Spectroscopy. Molecules 2020; 25:E5393. [PMID: 33218036 PMCID: PMC7698768 DOI: 10.3390/molecules25225393] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Revised: 11/15/2020] [Accepted: 11/16/2020] [Indexed: 11/16/2022] Open
Abstract
Detailed study of conformational rearrangements and dynamics of proteins is central to our understanding of their physiological functions and the loss of function. This review outlines the applications of the electron paramagnetic resonance (EPR) technique to study the structural aspects of proteins transitioning from a solution environment to the states in which they are associated with the surfaces of biological membranes or engineered nanoobjects. In the former case these structural transitions generally underlie functional protein states. The latter case is mostly relevant to the application of protein immobilization in biotechnological industries, developing methods for protein purification, etc. Therefore, evaluating the stability of the protein functional state is particularly important. EPR spectroscopy in the form of continuous-wave EPR or pulse EPR distance measurements in conjunction with protein spin labeling provides highly versatile and sensitive tools to characterize the changes in protein local dynamics as well as large conformational rearrangements. The technique can be widely utilized in studies of both protein-membrane and engineered nanoobject-protein complexes.
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Affiliation(s)
- Elka R Georgieva
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
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24
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Gamble Jarvi A, Casto J, Saxena S. Buffer effects on site directed Cu 2+-labeling using the double histidine motif. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 320:106848. [PMID: 33164758 DOI: 10.1016/j.jmr.2020.106848] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Revised: 09/25/2020] [Accepted: 10/07/2020] [Indexed: 05/09/2023]
Abstract
The double histidine, or dHis, motif has emerged as a powerful spin labeling tool to determine the conformations and dynamics, subunit orientation, native metal binding site location, and other physical characteristics of proteins by Cu2+-based electron paramagnetic resonance. Here, we investigate the efficacy of this technique in five common buffer systems, and show that buffer choice can impact the loading of Cu2+-NTA into dHis sites, and more generally, the sensitivity of the overall technique. We also present a standardized and optimized examination of labeling of the dHis motif with Cu2+-NTA for EPR based distance measurements. We provide optimal loading procedures, using representative EPR and UV/Vis data for each step in the process. From this data, we find that maximal dHis loading can be achieved in under 30 min with low temperature sample incubation. Using only these optimal procedures, we see up to a 28% increase in fully labeled proteins compared to previously published results in N-ethylmorpholine. Using both this optimized procedure as well as a more optimal buffer, we can achieve up to 80% fully loaded proteins, which corresponds to a 64% increase compared to the prior data. These results provide insight and deeper understanding of the dHis Cu2+-NTA system, the variables that impact its efficacy, and present a method by which these issues may be mitigated for the most efficient labeling.
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Affiliation(s)
- Austin Gamble Jarvi
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Joshua Casto
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Sunil Saxena
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA.
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25
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Matin TR, Heath GR, Huysmans GHM, Boudker O, Scheuring S. Millisecond dynamics of an unlabeled amino acid transporter. Nat Commun 2020; 11:5016. [PMID: 33024106 PMCID: PMC7538599 DOI: 10.1038/s41467-020-18811-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Accepted: 09/16/2020] [Indexed: 12/14/2022] Open
Abstract
Excitatory amino acid transporters (EAATs) are important in many physiological processes and crucial for the removal of excitatory amino acids from the synaptic cleft. Here, we develop and apply high-speed atomic force microscopy line-scanning (HS-AFM-LS) combined with automated state assignment and transition analysis for the determination of transport dynamics of unlabeled membrane-reconstituted GltPh, a prokaryotic EAAT homologue, with millisecond temporal resolution. We find that GltPh transporters can operate much faster than previously reported, with state dwell-times in the 50 ms range, and report the kinetics of an intermediate transport state with height between the outward- and inward-facing states. Transport domains stochastically probe transmembrane motion, and reversible unsuccessful excursions to the intermediate state occur. The presented approach and analysis methodology are generally applicable to study transporter kinetics at system-relevant temporal resolution. Excitatory amino acid transporters (EAATs) are crucial for the removal of excitatory amino acids from the synaptic cleft. Here authors combined high-speed atomic force microscopy line-scanning with automated state assignment for the determination of transport dynamics of GltPh, a prokaryotic EAAT homologue, with millisecond temporal resolution.
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Affiliation(s)
- Tina R Matin
- Department of Anesthesiology, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA.,Department of Physiology and Biophysics, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA
| | - George R Heath
- Department of Anesthesiology, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA.,Department of Physiology and Biophysics, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA
| | - Gerard H M Huysmans
- Department of Physiology and Biophysics, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA
| | - Olga Boudker
- Department of Physiology and Biophysics, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA.,Howard Hughes Medical Institute, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Simon Scheuring
- Department of Anesthesiology, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA. .,Department of Physiology and Biophysics, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA.
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26
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Huang Y, Wang X, Lv G, Razavi AM, Huysmans GHM, Weinstein H, Bracken C, Eliezer D, Boudker O. Use of paramagnetic 19F NMR to monitor domain movement in a glutamate transporter homolog. Nat Chem Biol 2020; 16:1006-1012. [PMID: 32514183 PMCID: PMC7442671 DOI: 10.1038/s41589-020-0561-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Accepted: 05/07/2020] [Indexed: 12/17/2022]
Abstract
In proteins where conformational changes are functionally important, the number of accessible states and their dynamics are often difficult to establish. Here we describe a novel 19F-NMR spectroscopy approach to probe dynamics of large membrane proteins. We labeled a glutamate transporter homolog with a 19F probe via cysteine chemistry and with a Ni2+ ion via chelation by a di-histidine motif. We used distance-dependent enhancement of the longitudinal relaxation of 19F nuclei by the paramagnetic metal to assign the observed resonances. We identified one inward- and two outward-facing states of the transporter, in which the substrate-binding site is near the extracellular and intracellular solutions, respectively. We then resolved the structure of the unanticipated second outward-facing state by cryo-EM. Finally, we showed that the rates of the conformational exchange are accessible from measurements of the metal-enhanced longitudinal relaxation of 19F nuclei.
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Affiliation(s)
- Yun Huang
- Department of Physiology & Biophysics, Weill Cornell Medicine, New York, NY, USA
- Howard Hughes Medical Institute, Chevy Chase, MD, USA
| | - Xiaoyu Wang
- Department of Physiology & Biophysics, Weill Cornell Medicine, New York, NY, USA
| | - Guohua Lv
- Department of Biochemistry, Weill Cornell Medicine, New York, NY, USA
- Division of Histology & Embryology, Medical College, Jinan University, Guangzhou, China
| | - Asghar M Razavi
- Department of Physiology & Biophysics, Weill Cornell Medicine, New York, NY, USA
| | - Gerard H M Huysmans
- Department of Physiology & Biophysics, Weill Cornell Medicine, New York, NY, USA
| | - Harel Weinstein
- Department of Physiology & Biophysics, Weill Cornell Medicine, New York, NY, USA
| | - Clay Bracken
- Department of Biochemistry, Weill Cornell Medicine, New York, NY, USA
| | - David Eliezer
- Department of Biochemistry, Weill Cornell Medicine, New York, NY, USA.
| | - Olga Boudker
- Department of Physiology & Biophysics, Weill Cornell Medicine, New York, NY, USA.
- Howard Hughes Medical Institute, Chevy Chase, MD, USA.
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27
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Transport rate of EAAT2 is regulated by amino acid located at the interface between the scaffolding and substrate transport domains. Neurochem Int 2020; 139:104792. [PMID: 32668264 DOI: 10.1016/j.neuint.2020.104792] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Revised: 05/19/2020] [Accepted: 06/21/2020] [Indexed: 01/24/2023]
Abstract
Excitatory Amino Acid Transporters (EAATs) are plasma membrane proteins responsible for maintenance of low extracellular concentrations of glutamate in the CNS. Dysfunction in their activity is implicated in various neurological disorders. Glutamate transport by EAATs occurs through the movement of the central transport domain relative to the scaffold domain in the EAAT membrane protein. Previous studies suggested that residues located within the interface of these two domains in EAAT2, the main subtype of glutamate transporter in the brain, are involved in regulating transport rates. We used mutagenesis, structure-function relationship, surface protein expression and electrophysiology studies, in transfected COS-7 cells and oocytes, to examine residue glycine at position 298, which is located within this interface. Mutation G298A results in increased transport rate without changes in surface expression, suggesting a more hydrophobic and larger alanine results in facilitated transport movement. The increased transport rate does not involve changes in sodium affinity. Electrophysiological currents show that G298A increase both transport and anion currents, suggesting faster transitions through the transport cycle. This work identifies a region critically involved in setting the glutamate transport rate.
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28
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Functional (un)cooperativity in elevator transport proteins. Biochem Soc Trans 2020; 48:1047-1055. [PMID: 32573703 DOI: 10.1042/bst20190970] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2020] [Revised: 05/26/2020] [Accepted: 05/28/2020] [Indexed: 11/17/2022]
Abstract
The activity of enzymes is subject to regulation at multiple levels. Cooperativity, the interconnected behavior of active sites within a protein complex, directly affects protein activity. Cooperativity is a mode of regulation that requires neither extrinsic factors nor protein modifications. Instead, it allows enzymes themselves to modulate reaction rates. Cooperativity is an important regulatory mechanism in soluble proteins, but also examples of cooperative membrane proteins have been described. In this review, we summarize the current knowledge on interprotomer cooperativity in elevator-type proteins, a class of membrane transporters characterized by large rigid-body movements perpendicular to the membrane, and highlight well-studied examples and experimental approaches.
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29
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Sahu ID, Lorigan GA. Electron Paramagnetic Resonance as a Tool for Studying Membrane Proteins. Biomolecules 2020; 10:E763. [PMID: 32414134 PMCID: PMC7278021 DOI: 10.3390/biom10050763] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Revised: 04/24/2020] [Accepted: 04/24/2020] [Indexed: 12/13/2022] Open
Abstract
Membrane proteins possess a variety of functions essential to the survival of organisms. However, due to their inherent hydrophobic nature, it is extremely difficult to probe the structure and dynamic properties of membrane proteins using traditional biophysical techniques, particularly in their native environments. Electron paramagnetic resonance (EPR) spectroscopy in combination with site-directed spin labeling (SDSL) is a very powerful and rapidly growing biophysical technique to study pertinent structural and dynamic properties of membrane proteins with no size restrictions. In this review, we will briefly discuss the most commonly used EPR techniques and their recent applications for answering structure and conformational dynamics related questions of important membrane protein systems.
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Affiliation(s)
- Indra D. Sahu
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Gary A. Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
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30
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Georgieva ER, Borbat PP, Fanouraki C, Freed JH. High-yield production in E. coli and characterization of full-length functional p13 II protein from human T-cell leukemia virus type 1. Protein Expr Purif 2020; 173:105659. [PMID: 32360379 DOI: 10.1016/j.pep.2020.105659] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2019] [Revised: 04/20/2020] [Accepted: 04/26/2020] [Indexed: 10/24/2022]
Abstract
Human T-cell leukemia virus type 1 is an oncovirus that causes aggressive adult T-cell leukemia but is also responsible for severe neurodegenerative and endocrine disorders. Combatting HTLV-1 infections requires a detailed understanding of the viral mechanisms in the host. Therefore, in vitro studies of important virus-encoded proteins would be critical. Our focus herein is on the HTLV-1-encoded regulatory protein p13II, which interacts with the inner mitochondrial membrane, increasing its permeability to cations (predominantly potassium, K+). Thereby, this protein affects mitochondrial homeostasis. We report on our progress in developing specific protocols for heterologous expression of p13II in E. coli, and methods for its purification and characterization. We succeeded in producing large quantities of highly-pure full-length p13II, deemed to be its fully functional form. Importantly, our particular approach based on the fusion of ubiquitin to the p13II C-terminus was instrumental in increasing the persistently low expression of soluble p13II in its native form. We subsequently developed approaches for protein spin labeling and a conformation study using double electron-electron resonance (DEER) spectroscopy and a fluorescence-based cation uptake assay for p13II in liposomes. Our DEER results point to large protein conformation changes occurring upon transition from the soluble to the membrane-bound state. The functional assay on p13II-assisted transport of thallium (Tl+) through the membrane, wherein Tl+ substituted for K+, suggests transmembrane potential involvement in p13II function. Our study lays the foundation for expansion of in vitro functional and structural investigations on p13II and would aid in the development of structure-based protein inhibitors and markers.
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Affiliation(s)
- Elka R Georgieva
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY, 14853, USA.
| | - Peter P Borbat
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY, 14853, USA; ACERT Center for Advanced ESR Technology, Cornell University, Ithaca, NY, 14853, USA
| | - Christina Fanouraki
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY, 14853, USA
| | - Jack H Freed
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY, 14853, USA; ACERT Center for Advanced ESR Technology, Cornell University, Ithaca, NY, 14853, USA
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31
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Wang X, Boudker O. Large domain movements through the lipid bilayer mediate substrate release and inhibition of glutamate transporters. eLife 2020; 9:58417. [PMID: 33155546 PMCID: PMC7682989 DOI: 10.7554/elife.58417] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Accepted: 11/05/2020] [Indexed: 01/21/2023] Open
Abstract
Glutamate transporters are essential players in glutamatergic neurotransmission in the brain, where they maintain extracellular glutamate below cytotoxic levels and allow for rounds of transmission. The structural bases of their function are well established, particularly within a model archaeal homolog, sodium, and aspartate symporter GltPh. However, the mechanism of gating on the cytoplasmic side of the membrane remains ambiguous. We report Cryo-EM structures of GltPh reconstituted into nanodiscs, including those structurally constrained in the cytoplasm-facing state and either apo, bound to sodium ions only, substrate, or blockers. The structures show that both substrate translocation and release involve movements of the bulky transport domain through the lipid bilayer. They further reveal a novel mode of inhibitor binding and show how solutes release is coupled to protein conformational changes. Finally, we describe how domain movements are associated with the displacement of bound lipids and significant membrane deformations, highlighting the potential regulatory role of the bilayer.
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Affiliation(s)
- Xiaoyu Wang
- Department of Physiology and Biophysics, Weill Cornell MedicineNew YorkUnited States
| | - Olga Boudker
- Department of Physiology and Biophysics, Weill Cornell MedicineNew YorkUnited States,Howard Hughes Medical InstituteChevy ChaseUnited States
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32
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Zhou W, Fiorin G, Anselmi C, Karimi-Varzaneh HA, Poblete H, Forrest LR, Faraldo-Gómez JD. Large-scale state-dependent membrane remodeling by a transporter protein. eLife 2019; 8:50576. [PMID: 31855177 PMCID: PMC6957315 DOI: 10.7554/elife.50576] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Accepted: 12/17/2019] [Indexed: 12/22/2022] Open
Abstract
That channels and transporters can influence the membrane morphology is increasingly recognized. Less appreciated is that the extent and free-energy cost of these deformations likely varies among different functional states of a protein, and thus, that they might contribute significantly to defining its mechanism. We consider the trimeric Na+-aspartate symporter GltPh, a homolog of an important class of neurotransmitter transporters, whose mechanism entails one of the most drastic structural changes known. Molecular simulations indicate that when the protomers become inward-facing, they cause deep, long-ranged, and yet mutually-independent membrane deformations. Using a novel simulation methodology, we estimate that the free-energy cost of this membrane perturbation is in the order of 6–7 kcal/mol per protomer. Compensating free-energy contributions within the protein or its environment must thus stabilize this inward-facing conformation for the transporter to function. We discuss these striking results in the context of existing experimental observations for this and other transporters.
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Affiliation(s)
- Wenchang Zhou
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States
| | - Giacomo Fiorin
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States
| | - Claudio Anselmi
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States
| | - Hossein Ali Karimi-Varzaneh
- Computational Structural Biology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Horacio Poblete
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States.,Computational Structural Biology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Lucy R Forrest
- Computational Structural Biology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - José D Faraldo-Gómez
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States
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33
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Allosteric activation of an ion channel triggered by modification of mechanosensitive nano-pockets. Nat Commun 2019; 10:4619. [PMID: 31601809 PMCID: PMC6787021 DOI: 10.1038/s41467-019-12591-x] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Accepted: 09/17/2019] [Indexed: 11/08/2022] Open
Abstract
Lipid availability within transmembrane nano-pockets of ion channels is linked with mechanosensation. However, the effect of hindering lipid-chain penetration into nano-pockets on channel structure has not been demonstrated. Here we identify nano-pockets on the large conductance mechanosensitive channel MscL, the high-pressure threshold channel. We restrict lipid-chain access to the nano-pockets by mutagenesis and sulfhydryl modification, and monitor channel conformation by PELDOR/DEER spectroscopy. For a single site located at the entrance of the nano-pockets and distal to the channel pore we generate an allosteric response in the absence of tension. Single-channel recordings reveal a significant decrease in the pressure activation threshold of the modified channel and a sub-conducting state in the absence of applied tension. Threshold is restored to wild-type levels upon reduction of the sulfhydryl modification. The modification associated with the conformational change restricts lipid access to the nano-pocket, interrupting the contact between the membrane and the channel that mediates mechanosensitivity.
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34
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Yu X, Plotnikova O, Bonin PD, Subashi TA, McLellan TJ, Dumlao D, Che Y, Dong YY, Carpenter EP, West GM, Qiu X, Culp JS, Han S. Cryo-EM structures of the human glutamine transporter SLC1A5 (ASCT2) in the outward-facing conformation. eLife 2019; 8:e48120. [PMID: 31580259 PMCID: PMC6800002 DOI: 10.7554/elife.48120] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Accepted: 10/02/2019] [Indexed: 12/17/2022] Open
Abstract
Alanine-serine-cysteine transporter 2 (ASCT2, SLC1A5) is the primary transporter of glutamine in cancer cells and regulates the mTORC1 signaling pathway. The SLC1A5 function involves finely tuned orchestration of two domain movements that include the substrate-binding transport domain and the scaffold domain. Here, we present cryo-EM structures of human SLC1A5 and its complex with the substrate, L-glutamine in an outward-facing conformation. These structures reveal insights into the conformation of the critical ECL2a loop which connects the two domains, thus allowing rigid body movement of the transport domain throughout the transport cycle. Furthermore, the structures provide new insights into substrate recognition, which involves conformational changes in the HP2 loop. A putative cholesterol binding site was observed near the domain interface in the outward-facing state. Comparison with the previously determined inward-facing structure of SCL1A5 provides a basis for a more integrated understanding of substrate recognition and transport mechanism in the SLC1 family.
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Affiliation(s)
- Xiaodi Yu
- Medicine DesignPfizer IncGrotonUnited States
| | | | | | | | | | | | - Ye Che
- Medicine DesignPfizer IncGrotonUnited States
| | - Yin Yao Dong
- Structural Genomics ConsortiumUniversity of OxfordOxfordUnited Kingdom
| | | | | | - Xiayang Qiu
- Medicine DesignPfizer IncGrotonUnited States
| | | | - Seungil Han
- Medicine DesignPfizer IncGrotonUnited States
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35
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Investigation of the allosteric coupling mechanism in a glutamate transporter homolog via unnatural amino acid mutagenesis. Proc Natl Acad Sci U S A 2019; 116:15939-15946. [PMID: 31332002 DOI: 10.1073/pnas.1907852116] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Glutamate transporters harness the ionic gradients across cell membranes for the concentrative uptake of glutamate. The sodium-coupled Asp symporter, GltPh is an archaeal homolog of glutamate transporters and has been extensively used to understand the transport mechanism. A critical aspect of the transport cycle in GltPh is the coupled binding of sodium and aspartate. Previous studies have suggested a major role for hairpin-2 (HP2), which functions as the extracellular gate for the aspartate binding site, in the coupled binding of sodium and aspartate to GltPh In this study, we develop a fluorescence assay for monitoring HP2 movement by incorporating tryptophan and the unnatural amino acid, p-cyanophenylalanine into GltPh We use the HP2 assays to show that HP2 opening with Na+ follows an induced-fit mechanism. We also determine how residues in the substrate binding site affect the opening and closing of HP2. Our data, combined with previous studies, provide the molecular sequence of events in the coupled binding of sodium and aspartate to GltPh.
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36
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Gamble Jarvi A, Cunningham TF, Saxena S. Efficient localization of a native metal ion within a protein by Cu2+-based EPR distance measurements. Phys Chem Chem Phys 2019; 21:10238-10243. [DOI: 10.1039/c8cp07143h] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
A native paramagnetic metal binding site in a protein is located with less than 2 Å resolution by a combination of double histidine (dHis) based Cu2+ labeling and long range distance measurements by EPR.
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Affiliation(s)
| | | | - Sunil Saxena
- Department of Chemistry
- University of Pittsburgh
- Pittsburgh
- USA
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37
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Srivastava M, Freed JH. Singular Value Decomposition Method To Determine Distance Distributions in Pulsed Dipolar Electron Spin Resonance: II. Estimating Uncertainty. J Phys Chem A 2018; 123:359-370. [PMID: 30525624 DOI: 10.1021/acs.jpca.8b07673] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
This paper is a continuation of the method introduced by Srivastava and Freed (2017) that is a new method based on truncated singular value decomposition (TSVD) for obtaining physical results from experimental signals without any need for Tikhonov regularization or other similar methods that require a regularization parameter. We show here how to estimate the uncertainty in the SVD-generated solutions. The uncertainty in the solution may be obtained by finding the minimum and maximum values over which the solution remains converged. These are obtained from the optimum range of singular value contributions, where the width of this region depends on the solution point location (e.g., distance) and the signal-to-noise ratio (SNR) of the signal. The uncertainty levels typically found are very small with substantial SNR of the (denoised) signal, emphasizing the reliability of the method. With poorer SNR, the method is still satisfactory but with greater uncertainty, as expected. Pulsed dipolar electron spin resonance spectroscopy experiments are used as an example, but this TSVD approach is general and thus applicable to any similar experimental method wherein singular matrix inversion is needed to obtain the physically relevant result. We show that the Srivastava-Freed TSVD method along with the estimate of uncertainty can be effectively applied to pulsed dipolar electron spin resonance signals with SNR > 30, and even for a weak signal (e.g., SNR ≈ 3) reliable results are obtained by this method, provided the signal is first denoised using wavelet transforms (WavPDS).
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38
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Oh S, Boudker O. Kinetic mechanism of coupled binding in sodium-aspartate symporter GltPh. eLife 2018; 7:37291. [PMID: 30255846 PMCID: PMC6175574 DOI: 10.7554/elife.37291] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Accepted: 09/25/2018] [Indexed: 01/09/2023] Open
Abstract
Many secondary active membrane transporters pump substrates against concentration gradients by coupling their uptake to symport of sodium ions. Symport requires the substrate and ions to be always transported together. Cooperative binding of the solutes is a key mechanism contributing to coupled transport in the sodium and aspartate symporter from Pyrococcus horikoshii GltPh. Here, we describe the kinetic mechanism of coupled binding for GltPh in the inward facing state. The first of the three coupled sodium ions, binds weakly and slowly, enabling the protein to accept the rest of the ions and the substrate. The last ion binds tightly, but is in rapid equilibrium with solution. Its release is required for the complex disassembly. Thus, the first ion serves to ‘open the door’ for the substrate, the last ion ‘locks the door’ once the substrate is in, and one ion contributes to both events.
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Affiliation(s)
- SeCheol Oh
- Department of Physiology & Biophysics, Weill Cornell Medicine, Cornell University, New York, United States
| | - Olga Boudker
- Department of Physiology & Biophysics, Weill Cornell Medicine, Cornell University, New York, United States.,Howard Hughes Medical Institute, Chevy Chase, United States
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39
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Single-molecule fluorescence studies on the conformational change of the ABC transporter MsbA. BIOPHYSICS REPORTS 2018. [DOI: 10.1007/s41048-018-0057-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
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40
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Riederer EA, Focke PJ, Georgieva ER, Akyuz N, Matulef K, Borbat PP, Freed JH, Blanchard SC, Boudker O, Valiyaveetil FI. A facile approach for the in vitro assembly of multimeric membrane transport proteins. eLife 2018; 7:36478. [PMID: 29889023 PMCID: PMC6025958 DOI: 10.7554/elife.36478] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Accepted: 06/08/2018] [Indexed: 11/13/2022] Open
Abstract
Membrane proteins such as ion channels and transporters are frequently homomeric. The homomeric nature raises important questions regarding coupling between subunits and complicates the application of techniques such as FRET or DEER spectroscopy. These challenges can be overcome if the subunits of a homomeric protein can be independently modified for functional or spectroscopic studies. Here, we describe a general approach for in vitro assembly that can be used for the generation of heteromeric variants of homomeric membrane proteins. We establish the approach using GltPh, a glutamate transporter homolog that is trimeric in the native state. We use heteromeric GltPh transporters to directly demonstrate the lack of coupling in substrate binding and demonstrate how heteromeric transporters considerably simplify the application of DEER spectroscopy. Further, we demonstrate the general applicability of this approach by carrying out the in vitro assembly of VcINDY, a Na+-coupled succinate transporter and CLC-ec1, a Cl-/H+ antiporter.
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Affiliation(s)
- Erika A Riederer
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, United States
| | - Paul J Focke
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, United States
| | - Elka R Georgieva
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, Unites States.,National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, United States
| | | | - Kimberly Matulef
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, United States
| | - Peter P Borbat
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, Unites States.,National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, United States
| | - Jack H Freed
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, Unites States.,National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, United States
| | | | - Olga Boudker
- Weill Cornell Medicine, New York, United States.,Howard Hughes Medical Institute, Maryland, United States
| | - Francis I Valiyaveetil
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, United States
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41
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Kortagere S, Mortensen OV, Xia J, Lester W, Fang Y, Srikanth Y, Salvino JM, Fontana ACK. Identification of Novel Allosteric Modulators of Glutamate Transporter EAAT2. ACS Chem Neurosci 2018; 9:522-534. [PMID: 29140675 DOI: 10.1021/acschemneuro.7b00308] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Dysfunction of excitatory amino acid transporters (EAATs) has been implicated in the pathogenesis of various neurological disorders, such as stroke, brain trauma, epilepsy, and neurodegenerative diseases, among others. EAAT2 is the main subtype responsible for glutamate clearance in the brain, having a key role in regulating transmission and preventing excitotoxicity. Therefore, compounds that increase the expression or activity of EAAT2 have therapeutic potential for neuroprotection. Previous studies identified molecular determinants for EAAT2 transport stimulation in a structural domain that lies at the interface of the rigid trimerization domain and the central substrate binding transport domain. In this work, a hybrid structure based approach was applied, based on this molecular domain, to create a high-resolution pharmacophore. Subsequently, virtual screening of a library of small molecules was performed, identifying 10 hit molecules that interact at the proposed domain. Among these, three compounds were determined to be activators, four were inhibitors, and three had no effect on EAAT2-mediated transport in vitro. Further characterization of the two best ranking EAAT2 activators for efficacy, potency, and selectivity for glutamate over monoamine transporters subtypes and NMDA receptors and for efficacy in cultured astrocytes is demonstrated. Mutagenesis studies suggest that the EAAT2 activators interact with residues forming the interface between the trimerization and transport domains. These compounds enhance the glutamate translocation rate, with no effect on substrate interaction, suggesting an allosteric mechanism. The identification of these novel positive allosteric modulators of EAAT2 offers an innovative approach for the development of therapies based on glutamate transport enhancement.
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Affiliation(s)
- Sandhya Kortagere
- Department of Microbiology and Immunology, Centers for Molecular Parasitology, Virology and Translational Neuroscience, Institute for Molecular Medicine, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129, United States
| | - Ole V. Mortensen
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Jingsheng Xia
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - William Lester
- Analytical Chemistry, Division of Pre-Clinical Innovation (DPI), NCATS, National Institutes of Health, Rockville, Maryland 20850, United States
| | - Yuhong Fang
- Analytical Chemistry, Division of Pre-Clinical Innovation (DPI), NCATS, National Institutes of Health, Rockville, Maryland 20850, United States
| | - Yellamelli Srikanth
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Joseph M. Salvino
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Andréia C. K. Fontana
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
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42
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Gmeiner C, Dorn G, Allain FHT, Jeschke G, Yulikov M. Spin labelling for integrative structure modelling: a case study of the polypyrimidine-tract binding protein 1 domains in complexes with short RNAs. Phys Chem Chem Phys 2018; 19:28360-28380. [PMID: 29034946 DOI: 10.1039/c7cp05822e] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
A combined method, employing NMR and EPR spectroscopies, has demonstrated its strength in solving structures of protein/RNA and other types of biomolecular complexes. This method works particularly well when the large biomolecular complex consists of a limited number of rigid building blocks, such as RNA-binding protein domains (RBDs). A variety of spin labels is available for such studies, allowing for conventional as well as spectroscopically orthogonal double electron-electron resonance (DEER) measurements in EPR. In this work, we compare different types of nitroxide-based and Gd(iii)-based spin labels attached to isolated RBDs of the polypyrimidine-tract binding protein 1 (PTBP1) and to short RNA fragments. In particular, we demonstrate experiments on spectroscopically orthogonal labelled RBD/RNA complexes. For all experiments we analyse spin labelling, DEER method performance, resulting distance distributions, and their consistency with the predictions from the spin label rotamers analysis. This work provides a set of intra-domain calibration DEER data, which can serve as a basis to start structure determination of the full length PTBP1 complex with an RNA derived from encephalomycarditis virus (EMCV) internal ribosomal entry site (IRES). For a series of tested labelling sites, we discuss their particular advantages and drawbacks in such a structure determination approach.
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Affiliation(s)
- Christoph Gmeiner
- Laboratory of Physical Chemistry, ETH Zurich, Zurich, 8093, Switzerland.
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43
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The contribution of modern EPR to structural biology. Emerg Top Life Sci 2018; 2:9-18. [PMID: 33525779 PMCID: PMC7288997 DOI: 10.1042/etls20170143] [Citation(s) in RCA: 77] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2017] [Revised: 12/22/2017] [Accepted: 01/02/2018] [Indexed: 02/08/2023]
Abstract
Electron paramagnetic resonance (EPR) spectroscopy combined with site-directed spin labelling is applicable to biomolecules and their complexes irrespective of system size and in a broad range of environments. Neither short-range nor long-range order is required to obtain structural restraints on accessibility of sites to water or oxygen, on secondary structure, and on distances between sites. Many of the experiments characterize a static ensemble obtained by shock-freezing. Compared with characterizing the dynamic ensemble at ambient temperature, analysis is simplified and information loss due to overlapping timescales of measurement and system dynamics is avoided. The necessity for labelling leads to sparse restraint sets that require integration with data from other methodologies for building models. The double electron–electron resonance experiment provides distance distributions in the nanometre range that carry information not only on the mean conformation but also on the width of the native ensemble. The distribution widths are often inconsistent with Anfinsen's concept that a sequence encodes a single native conformation defined at atomic resolution under physiological conditions.
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44
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Affiliation(s)
- Katrin Ackermann
- Biomedical Sciences Research Complex, Centre of Magnetic Resonance and EaStCHEM School of Chemistry, University of St Andrews, St Andrews, KY16 9ST, Scotland
| | - Bela E. Bode
- Biomedical Sciences Research Complex, Centre of Magnetic Resonance and EaStCHEM School of Chemistry, University of St Andrews, St Andrews, KY16 9ST, Scotland
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45
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Wang J, Albers T, Grewer C. Energy Landscape of the Substrate Translocation Equilibrium of Plasma-Membrane Glutamate Transporters. J Phys Chem B 2017; 122:28-39. [PMID: 29218993 DOI: 10.1021/acs.jpcb.7b09059] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Glutamate transporters maintain a large glutamate concentration gradient across synaptic membranes and are, thus, critical for functioning of the excitatory synapse. Mammalian glutamate transporters concentrate glutamate inside cells through energetic coupling of glutamate flux to the transmembrane concentration gradient of Na+. Structural models based on an archeal homologue, GltPh, suggest an elevator-like carrier mechanism. However, the energetic determinants of this carrier-based movement are not well understood. Although electrostatics play an important role in governing these energetics, their implication on transport dynamics has not been studied. Here, we combine a pre-steady-state kinetic analysis of the translocation equilibrium with electrostatic computations to gain insight into the energetics of the translocation process. Our results show the biphasic nature of translocation, consistent with the existence of an intermediate on the translocation pathway. In the absence of voltage, the equilibrium is shifted to the outward-facing configuration. Electrostatic computations confirm the intermediate state and show that the elevator-like movement is energetically feasible in the presence of bound Na+ ions, whereas a substrate-hopping model is energetically prohibitive. Our results highlight the critical contribution of charge compensation to transport and add to results from previous molecular dynamics simulations for improved understanding of the glutamate translocation process.
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Affiliation(s)
- Jiali Wang
- Department of Chemistry, Binghamton University , Binghamton, New York 13902, United States
| | - Thomas Albers
- Department of Chemistry, Binghamton University , Binghamton, New York 13902, United States
| | - Christof Grewer
- Department of Chemistry, Binghamton University , Binghamton, New York 13902, United States
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Ackermann K, Pliotas C, Valera S, Naismith JH, Bode BE. Sparse Labeling PELDOR Spectroscopy on Multimeric Mechanosensitive Membrane Channels. Biophys J 2017; 113:1968-1978. [PMID: 29117521 PMCID: PMC5685675 DOI: 10.1016/j.bpj.2017.09.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Revised: 08/31/2017] [Accepted: 09/05/2017] [Indexed: 11/17/2022] Open
Abstract
Pulse electron paramagnetic resonance (EPR) is being applied to ever more complex biological systems comprising multiple subunits. Membrane channel proteins are of great interest as pulse EPR reports on functionally significant but distinct conformational states in a native environment without the need for crystallization. Pulse EPR, in the form of pulsed electron-electron double resonance (PELDOR), using site-directed spin labeling, is most commonly employed to accurately determine distances (in the nanometer range) between different regions of the structure. However, PELDOR data analysis is more challenging in systems containing more than two spins (e.g., homomultimers) due to distorting multispin effects. Without suppression of these effects, much of the information contained in PELDOR data cannot be reliably retrieved. Thus, it is of utmost importance for future PELDOR applications in structural biology to develop suitable approaches that can overcome the multispin problem. Here, two different approaches for suppressing multispin effects in PELDOR, sparse labeling of the protein (reducing the labeling efficiency f) and reducing the excitation probability of spins (λ), are compared on two distinct bacterial mechanosensitive channels. For both the pentameric channel of large conductance (MscL) and the heptameric channel of small conductance (MscS) of Escherichia coli, mutants containing a spin label in the cytosolic or the transmembrane region were tested. Data demonstrate that distance distributions can be significantly improved with either approach compared to the standard PELDOR measurement, and confirm that λ < 1/(n−1) is needed to sufficiently suppress multispin effects (with n being the number of spins in the system). A clear advantage of the sparse labeling approach is demonstrated for the cytosolic mutants due to a significantly smaller loss in sensitivity. For the transmembrane mutants, this advantage is less pronounced but still useful for MscS, but performance is inferior for MscL possibly due to structural perturbations by the bulkier diamagnetic spin label analog.
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Affiliation(s)
- Katrin Ackermann
- Centre of Magnetic Resonance, University of St Andrews, North Haugh, St Andrews, Fife, United Kingdom; Biomedical Sciences Research Complex and EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, United Kingdom
| | - Christos Pliotas
- Centre of Magnetic Resonance, University of St Andrews, North Haugh, St Andrews, Fife, United Kingdom; Biomedical Sciences Research Complex and EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, United Kingdom
| | - Silvia Valera
- Centre of Magnetic Resonance, University of St Andrews, North Haugh, St Andrews, Fife, United Kingdom; Biomedical Sciences Research Complex and EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, United Kingdom
| | - James H Naismith
- Biomedical Sciences Research Complex and EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, United Kingdom
| | - Bela E Bode
- Centre of Magnetic Resonance, University of St Andrews, North Haugh, St Andrews, Fife, United Kingdom; Biomedical Sciences Research Complex and EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, United Kingdom.
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Srivastava M, Freed JH. Singular Value Decomposition Method to Determine Distance Distributions in Pulsed Dipolar Electron Spin Resonance. J Phys Chem Lett 2017; 8:5648-5655. [PMID: 29099190 PMCID: PMC5708871 DOI: 10.1021/acs.jpclett.7b02379] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Regularization is often utilized to elicit the desired physical results from experimental data. The recent development of a denoising procedure yielding about 2 orders of magnitude in improvement in SNR obviates the need for regularization, which achieves a compromise between canceling effects of noise and obtaining an estimate of the desired physical results. We show how singular value decomposition (SVD) can be employed directly on the denoised data, using pulse dipolar electron spin resonance experiments as an example. Such experiments are useful in measuring distances and their distributions, P(r) between spin labels on proteins. In noise-free model cases exact results are obtained, but even a small amount of noise (e.g., SNR = 850 after denoising) corrupts the solution. We develop criteria that precisely determine an optimum approximate solution, which can readily be automated. This method is applicable to any signal that is currently processed with regularization of its SVD analysis.
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Affiliation(s)
- Madhur Srivastava
- National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York 14853, United States
- Meinig School of Biomedical Engineering, Cornell University, Ithaca, New York 14853, United States
| | - Jack H. Freed
- National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York 14853, United States
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
- Corresponding Author:
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Arkhipova V, Guskov A, Slotboom DJ. Analysis of the quality of crystallographic data and the limitations of structural models. J Gen Physiol 2017; 149:1091-1103. [PMID: 29089418 PMCID: PMC5715909 DOI: 10.1085/jgp.201711852] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2017] [Accepted: 10/10/2017] [Indexed: 12/22/2022] Open
Abstract
Arkhipova et al. caution that the limitations of structural models be taken into account when interpreting crystallographic data. Crystal structures provide visual models of biological macromolecules, which are widely used to interpret data from functional studies and generate new mechanistic hypotheses. Because the quality of the collected x-ray diffraction data directly affects the reliability of the structural model, it is essential that the limitations of the models are carefully taken into account when making interpretations. Here we use the available crystal structures of members of the glutamate transporter family to illustrate the importance of inspecting the data that underlie the structural models. Crystal structures of glutamate transporters in multiple different conformations have been solved, but most structures were determined at relatively low resolution, with deposited models based on crystallographic data of moderate quality. We use these examples to demonstrate the extent to which mechanistic interpretations can be made safely.
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Affiliation(s)
- Valentina Arkhipova
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, Zernike Institute for Advanced Materials, University of Groningen, Groningen, Netherlands
| | - Albert Guskov
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, Zernike Institute for Advanced Materials, University of Groningen, Groningen, Netherlands
| | - Dirk-Jan Slotboom
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, Zernike Institute for Advanced Materials, University of Groningen, Groningen, Netherlands
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Gmeiner C, Klose D, Mileo E, Belle V, Marque SRA, Dorn G, Allain FHT, Guigliarelli B, Jeschke G, Yulikov M. Orthogonal Tyrosine and Cysteine Site-Directed Spin Labeling for Dipolar Pulse EPR Spectroscopy on Proteins. J Phys Chem Lett 2017; 8:4852-4857. [PMID: 28933855 DOI: 10.1021/acs.jpclett.7b02220] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Site-directed spin labeling of native tyrosine residues in isolated domains of the protein PTBP1, using a Mannich-type reaction, was combined with conventional spin labeling of cysteine residues. Double electron-electron resonance (DEER) EPR measurements were performed for both the nitroxide-nitroxide and Gd(III)-nitroxide label combinations within the same protein molecule. For the prediction of distance distributions from a structure model, rotamer libraries were generated for the two linker forms of the tyrosine-reactive isoindoline-based nitroxide radical Nox. Only moderate differences exist between the spatial spin distributions for the two linker forms of Nox. This strongly simplifies DEER data analysis, in particular, if only mean distances need to be predicted.
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Affiliation(s)
- Christoph Gmeiner
- Laboratory of Physical Chemistry, ETH Zurich , Zurich 8093, Switzerland
| | - Daniel Klose
- Laboratory of Physical Chemistry, ETH Zurich , Zurich 8093, Switzerland
| | - Elisabetta Mileo
- Aix Marseille Univ , CNRS, BIP, Laboratoire de Bioénergétique et Ingénierie des Protéines, Marseille 13402, France
| | - Valérie Belle
- Aix Marseille Univ , CNRS, BIP, Laboratoire de Bioénergétique et Ingénierie des Protéines, Marseille 13402, France
| | - Sylvain R A Marque
- Aix Marseille Univ , CNRS, ICR, Institut de Chimie Radicalaire, Marseille 13397, France
- N. N. Vorozhtsov Novosibirsk Insititute of Organic Chemistry , 630090 Novosibirsk, Russia
| | - Georg Dorn
- Institute of Molecular Biology and Biophysics, ETH Zurich , Zurich 8093, Switzerland
| | - Frédéric H T Allain
- Institute of Molecular Biology and Biophysics, ETH Zurich , Zurich 8093, Switzerland
| | - Bruno Guigliarelli
- Aix Marseille Univ , CNRS, BIP, Laboratoire de Bioénergétique et Ingénierie des Protéines, Marseille 13402, France
| | - Gunnar Jeschke
- Laboratory of Physical Chemistry, ETH Zurich , Zurich 8093, Switzerland
| | - Maxim Yulikov
- Laboratory of Physical Chemistry, ETH Zurich , Zurich 8093, Switzerland
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50
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Carrington B, Myers WK, Horanyi P, Calmiano M, Lawson ADG. Natural Conformational Sampling of Human TNFα Visualized by Double Electron-Electron Resonance. Biophys J 2017; 113:371-380. [PMID: 28746848 PMCID: PMC5529296 DOI: 10.1016/j.bpj.2017.06.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 05/05/2017] [Accepted: 06/06/2017] [Indexed: 12/20/2022] Open
Abstract
Double electron-electron resonance in conjunction with site-directed spin labeling has been used to probe natural conformational sampling of the human tumor necrosis factor α trimer. We suggest a previously unreported, predeoligomerization conformation of the trimer that has been shown to be sampled at low frequency. A model of this trimeric state has been constructed based on crystal structures using the double-electron-electron-resonance distances. The model shows one of the protomers to be rotated and tilted outward at the tip end, leading to a breaking of the trimerous symmetry and distortion at a receptor-binding interface. The new structure offers opportunities to modulate the biological activity of tumor necrosis factor α through stabilization of the distorted trimer with small molecules.
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Affiliation(s)
| | - William K Myers
- Department of Inorganic Chemistry, University of Oxford, Oxford, United Kingdom
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