Structural basis for ion selectivity revealed by high-resolution crystal structure of Mg2+ channel MgtE

Hironori Takeda, Motoyuki Hattori, Tomohiro Nishizawa, Keitaro Yamashita, Syed T. A. Shah, Martin Caffrey, Andrés D. Maturana, Ryuichiro Ishitani () and Osamu Nureki ()
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Hironori Takeda: Graduate School of Science, University of Tokyo
Motoyuki Hattori: Graduate School of Science, University of Tokyo
Tomohiro Nishizawa: Graduate School of Science, University of Tokyo
Keitaro Yamashita: SR Life Science Instrumentation Unit, RIKEN SPring-8 Center
Syed T. A. Shah: Membrane Structural and Functional Biology Group, School of Medicine, and School of Biochemistry and Immunology, Trinity College Dublin
Martin Caffrey: Membrane Structural and Functional Biology Group, School of Medicine, and School of Biochemistry and Immunology, Trinity College Dublin
Andrés D. Maturana: Graduate School of Bioagricultural Sciences, Nagoya University
Ryuichiro Ishitani: Graduate School of Science, University of Tokyo
Osamu Nureki: Graduate School of Science, University of Tokyo

Nature Communications, 2014, vol. 5, issue 1, 1-10

Abstract: Abstract Magnesium is the most abundant divalent cation in living cells and is crucial to several biological processes. MgtE is a Mg2+ channel distributed in all domains of life that contributes to the maintenance of cellular Mg2+ homeostasis. Here we report the high-resolution crystal structures of the transmembrane domain of MgtE, bound to Mg2+, Mn2+ and Ca2+. The high-resolution Mg2+-bound crystal structure clearly visualized the hydrated Mg2+ ion within its selectivity filter. Based on those structures and biochemical analyses, we propose a cation selectivity mechanism for MgtE in which the geometry of the hydration shell of the fully hydrated Mg2+ ion is recognized by the side-chain carboxylate groups in the selectivity filter. This is in contrast to the K+-selective filter of KcsA, which recognizes a dehydrated K+ ion. Our results further revealed a cation-binding site on the periplasmic side, which regulate channel opening and prevents conduction of near-cognate cations.

Date: 2014
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DOI: 10.1038/ncomms6374

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