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Nastasa V, Stavarache C, Hanganu A, Coroaba A, Nicolescu A, Deleanu C, Sadet A, Vasos PR. Hyperpolarised NMR to follow water proton transport through membrane channels via exchange with biomolecules. Faraday Discuss 2019; 209:67-82. [PMID: 29989626 DOI: 10.1039/c8fd00021b] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Water uptake in vesicles and the subsequent exchange between water protons and amide -NH protons in amino acids can be followed by a new, highly sensitive, type of magnetic resonance spectroscopy: dynamic nuclear polarisation (DNP)-enhanced NMR in the liquid state. Water hydrogen atoms are detected prior to and after their transfer to molecular sites in peptides and proteins featuring highly-accessible proton-exchangeable groups, as is the case for the -NH groups of intrinsically disordered proteins. The detected rates for amide proton-water proton exchange can be modulated by membrane-crossing rates, when a membrane channel is interposed. We hyperpolarised water proton spins via dynamic nuclear polarisation followed by sample dissolution (d-DNP) and transferred the created polarisation to -NH groups with high solvent accessibility in an intrinsically disordered protein domain. This domain is the membrane anchor of c-Src kinase, whose activity controls cell proliferation. The hindrance of effective water proton transfer rate constants observed in free solvent when a membrane-crossing step is involved is discussed. This study aims to assess the feasibility of recently-introduced hyperpolarised (DNP-enhanced) NMR to assess water membrane crossing dynamics.
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Affiliation(s)
- Viorel Nastasa
- Extreme Light Infrastructure - Nuclear Physics (ELI-NP), Horia Hulubei Institute for Nuclear Physics (IFIN-HH), Reactorului Str., 30, Magurele Campus, Bucharest, Romania.
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Ehrl B, Mogusu EO, Kim K, Hofstetter H, Pedersen JA, Elsner M. High Permeation Rates in Liposome Systems Explain Rapid Glyphosate Biodegradation Associated with Strong Isotope Fractionation. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2018; 52:7259-7268. [PMID: 29790342 PMCID: PMC7193547 DOI: 10.1021/acs.est.8b01004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2018] [Revised: 05/17/2018] [Accepted: 05/23/2018] [Indexed: 05/22/2023]
Abstract
Bacterial uptake of charged organic pollutants such as the widely used herbicide glyphosate is typically attributed to active transporters, whereas passive membrane permeation as an uptake pathway is usually neglected. For 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC) liposomes, the pH-dependent apparent membrane permeation coefficients ( Papp) of glyphosate, determined by nuclear magnetic resonance (NMR) spectroscopy, varied from Papp (pH 7.0) = 3.7 (±0.3) × 10-7 m·s-1 to Papp (pH 4.1) = 4.2 (±0.1) × 10-6 m·s-1. The magnitude of this surprisingly rapid membrane permeation depended on glyphosate speciation and was, at circumneutral pH, in the range of polar, noncharged molecules. These findings point to passive membrane permeation as a potential uptake pathway during glyphosate biodegradation. To test this hypothesis, a Gram-negative glyphosate degrader, Ochrobactrum sp. FrEM, was isolated from glyphosate-treated soil and glyphosate permeation rates inferred from the liposome model system were compared to bacterial degradation rates. Estimated maximum permeation rates were, indeed, 2 orders of magnitude higher than degradation rates of glyphosate. In addition, biodegradation of millimolar glyphosate concentrations gave rise to pronounced carbon isotope fractionation with an apparent kinetic isotope effect, AKIEcarbon, of 1.014 ± 0.003. This value lies in the range typical of non-masked enzymatic isotope fractionation demonstrating that glyphosate biodegradation was not subject to mass transfer limitations and glyphosate exchange across the cell membrane was rapid relative to enzymatic turnover.
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Affiliation(s)
- Benno
N. Ehrl
- Institute
of Groundwater Ecology, Helmholtz Zentrum
München, Ingolstädter
Landstrasse 1, 85764 Neuherberg, Germany
| | - Emmanuel O. Mogusu
- Institute
of Groundwater Ecology, Helmholtz Zentrum
München, Ingolstädter
Landstrasse 1, 85764 Neuherberg, Germany
- Department
of Chemistry, Mwenge Catholic University, P.O. Box 1226, Moshi, Tanzania
| | - Kyoungtea Kim
- Molecular
and Environmental Toxicology Center, University
of Wisconsin, Madison, Wisconsin 53706, United States
| | - Heike Hofstetter
- Department
of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
| | - Joel A. Pedersen
- Molecular
and Environmental Toxicology Center, University
of Wisconsin, Madison, Wisconsin 53706, United States
- Department
of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
- Departments
of Soil Science and Civil & Environmental Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
| | - Martin Elsner
- Institute
of Groundwater Ecology, Helmholtz Zentrum
München, Ingolstädter
Landstrasse 1, 85764 Neuherberg, Germany
- Institute
of Hydrochemistry, Chair for Analytical Chemistry and Water Chemistry, Technical University of Munich, Marchioninistrasse 17, 81377 Munich, Germany
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