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Measurement of (15)N longitudinal relaxation rates in (15)NH4(+) spin systems to characterise rotational correlation times and chemical exchange.

Hansen, DF; (2017) Measurement of (15)N longitudinal relaxation rates in (15)NH4(+) spin systems to characterise rotational correlation times and chemical exchange. Journal of Magnetic Resonance , 279 pp. 91-98. 10.1016/j.jmr.2017.01.015. Green open access

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Abstract

Many chemical and biological processes rely on the movement of monovalent cations and an understanding of such processes can therefore only be achieved by characterising the dynamics of the involved ions. It has recently been shown that (15)N-ammonium can be used as a proxy for potassium to probe potassium binding in bio-molecules such as DNA quadruplexes and enzymes. Moreover, equations have been derived to describe the time-evolution of (15)N-based spin density operator elements of (15)NH4(+) spin systems. Herein NMR pulse sequences are derived to select specific spin density matrix elements of the (15)NH4(+) spin system and to measure their longitudinal relaxation in order to characterise the rotational correlation time of the (15)NH4(+) ion as well as report on chemical exchange events of the (15)NH4(+) ion. Applications to (15)NH4(+) in acidic aqueous solutions are used to cross-validate the developed pulse sequence while measurements of spin-relaxation rates of (15)NH4(+) bound to a 41kDa domain of the bacterial Hsp70 homologue DnaK are presented to show the general applicability of the derived pulse sequence. The rotational correlation time obtained for (15)N-ammonium bound to DnaK is similar to the correlation time that describes the rotation about the threefold axis of a methyl group. The methodology presented here provides, together with the previous theoretical framework, an important step towards characterising the motional properties of cations in macromolecular systems.

Type: Article
Title: Measurement of (15)N longitudinal relaxation rates in (15)NH4(+) spin systems to characterise rotational correlation times and chemical exchange.
Location: United States
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.jmr.2017.01.015
Publisher version: http://dx.doi.org/10.1016/j.jmr.2017.01.015
Language: English
Additional information: © 2017 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Keywords: AX(4) spin systems, Ammonium, Chemical exchange, NMR, Nuclear spin relaxation
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences > Structural and Molecular Biology
URI: https://discovery.ucl.ac.uk/id/eprint/1559192
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