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Maruyama T, Imai S, Kusakizako T, Hattori M, Ishitani R, Nureki O, Ito K, Maturana AD, Shimada I, Osawa M. Functional roles of Mg 2+ binding sites in ion-dependent gating of a Mg 2+ channel, MgtE, revealed by solution NMR. eLife 2018; 7:31596. [PMID: 29611805 PMCID: PMC5882242 DOI: 10.7554/elife.31596] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2017] [Accepted: 03/25/2018] [Indexed: 01/30/2023] Open
Abstract
Magnesium ions (Mg2+) are divalent cations essential for various cellular functions. Mg2+ homeostasis is maintained through Mg2+ channels such as MgtE, a prokaryotic Mg2+ channel whose gating is regulated by intracellular Mg2+ levels. Our previous crystal structure of MgtE in the Mg2+-bound, closed state revealed the existence of seven crystallographically-independent Mg2+-binding sites, Mg1-Mg7. The role of Mg2+-binding to each site in channel closure remains unknown. Here, we investigated Mg2+-dependent changes in the structure and dynamics of MgtE using nuclear magnetic resonance spectroscopy. Mg2+-titration experiments, using wild-type and mutant forms of MgtE, revealed that the Mg2+ binding sites Mg1, Mg2, Mg3, and Mg6, exhibited cooperativity and a higher affinity for Mg2+, enabling the remaining Mg2+ binding sites, Mg4, Mg5, and Mg7, to play important roles in channel closure. This study revealed the role of each Mg2+-binding site in MgtE gating, underlying the mechanism of cellular Mg2+ homeostasis.
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Affiliation(s)
- Tatsuro Maruyama
- Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
| | - Shunsuke Imai
- Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
| | - Tsukasa Kusakizako
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan
| | - Motoyuki Hattori
- State Key Laboratory of Genetic Engineering, School of Life Sciences, Fudan University, Shanghai, China.,Collaborative Innovation Center of Genetics and Development, School of Life Sciences, Fudan University, Shanghai, China.,Department of Physiology and Biophysics, School of Life Sciences, Fudan University, Shanghai, China
| | - Ryuichiro Ishitani
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan
| | - Osamu Nureki
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan
| | - Koichi Ito
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Chiba, Japan
| | - Andrès D Maturana
- Department of Bioengineering Sciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
| | - Ichio Shimada
- Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
| | - Masanori Osawa
- Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan.,Division of Physics for Life Functions, Faculty of Pharmacy, Keio University, Tokyo, Japan
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Jeong BC, Park SH, Yoo KS, Shin JS, Song HK. Change in single cystathionine β-synthase domain-containing protein from a bent to flat conformation upon adenosine monophosphate binding. J Struct Biol 2013; 183:40-6. [PMID: 23664870 DOI: 10.1016/j.jsb.2013.04.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Revised: 04/25/2013] [Accepted: 04/28/2013] [Indexed: 12/25/2022]
Abstract
Cystathionine β-synthase (CBS) domains are small intracellular modules that can act as binding domains for adenosine derivatives, and they may regulate the activity of associated enzymes or other functional domains. Among these, the single CBS domain-containing proteins, CBSXs, from Arabidopsis thaliana, have recently been identified as redox regulators of the thioredoxin system. Here, the crystal structure of CBSX2 in complex with adenosine monophosphate (AMP) is reported at 2.2Å resolution. The structure of dimeric CBSX2 with bound-AMP is shown to be approximately flat, which is in stark contrast to the bent form of apo-CBSXs. This conformational change in quaternary structure is triggered by a local structural change of the unique α5 helix, and by moving each loop P into an open conformation to accommodate incoming ligands. Furthermore, subtle rearrangement of the dimer interface triggers movement of all subunits, and consequently, the bent structure of the CBSX2 dimer becomes a flat structure. This reshaping of the structure upon complex formation with adenosine-containing ligand provides evidence that ligand-induced conformational reorganization of antiparallel CBS domains is an important regulatory mechanism.
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Affiliation(s)
- Byung-Cheon Jeong
- School of Life Sciences and Biotechnology, Korea University, Seoul 136-701, South Korea
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3
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Hattori M, Iwase N, Furuya N, Tanaka Y, Tsukazaki T, Ishitani R, Maguire ME, Ito K, Maturana A, Nureki O. Mg(2+)-dependent gating of bacterial MgtE channel underlies Mg(2+) homeostasis. EMBO J 2009; 28:3602-12. [PMID: 19798051 DOI: 10.1038/emboj.2009.288] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2009] [Accepted: 09/04/2009] [Indexed: 11/09/2022] Open
Abstract
The MgtE family of Mg(2+) transporters is ubiquitously distributed in all phylogenetic domains. Recent crystal structures of the full-length MgtE and of its cytosolic domain in the presence and absence of Mg(2+) suggested a Mg(2+)-homeostasis mechanism, in which the MgtE cytosolic domain acts as a 'Mg(2+) sensor' to regulate the gating of the ion-conducting pore in response to the intracellular Mg(2+) concentration. However, complementary functional analyses to confirm the proposed model have been lacking. Moreover, the limited resolution of the full-length structure precluded an unambiguous characterization of these regulatory divalent-cation-binding sites. Here, we showed that MgtE is a highly Mg(2+)-selective channel gated by Mg(2+) and elucidated the Mg(2+)-dependent gating mechanism of MgtE, using X-ray crystallographic, genetic, biochemical, and electrophysiological analyses. These structural and functional results have clarified the control of Mg(2+) homeostasis through cooperative Mg(2+) binding to the MgtE cytosolic domain.
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Affiliation(s)
- Motoyuki Hattori
- Department of Basic Medical Sciences, Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo, Japan
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Abstract
Considering the biological abundance and importance of Mg2+, there is a surprising lack of information regarding the proteins that transport Mg2+, the mechanisms by which they do so, and their physiological roles within the cell. The best characterized Mg2+ channel to date is the bacterial protein CorA, present in a wide range of bacterial species. The CorA homolog Mrs2 forms the mitochondrial Mg2+ channel in all eukaryotes. Physiologically, CorA is involved in bacterial pathogenesis, and the Mrs2 eukaryotic homolog is essential for cell survival. A second Mg2+ channel widespread in bacteria is MgtE. Its eukaryotic homologs are the SLC41 family of carriers. Physiological roles for MgtE and its homologs have not been established. Recently, the crystal structures for the bacterial CorA and MgtE Mg2+ channels were solved, the first structures of any divalent cation channel. As befits the unique biological chemistry of Mg2+, both structures are unique, unlike that of any other channel or transporter. Although structurally quite different, both CorA and MgtE appear to be gated in a similar manner through multiple Mg2+ binding sites in the cytosolic domain of the channels. These sites essentially serve as Mg2+ "sensors" of cytosolic Mg2+ concentration. Many questions about these channels remain, however, including the molecular basis of Mg2+ selectivity and the physiological role(s) of their eukaryotic homologs.
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Affiliation(s)
- Andrea S Moomaw
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
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Hattori M, Tanaka Y, Fukai S, Ishitani R, Nureki O. Crystal structure of the MgtE Mg2+ transporter. Nature 2007; 448:1072-5. [PMID: 17700703 DOI: 10.1038/nature06093] [Citation(s) in RCA: 148] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Accepted: 07/16/2007] [Indexed: 11/09/2022]
Abstract
The magnesium ion Mg2+ is a vital element involved in numerous physiological processes. Mg2+ has the largest hydrated radius among all cations, whereas its ionic radius is the smallest. It remains obscure how Mg2+ transporters selectively recognize and dehydrate the large, fully hydrated Mg2+ cation for transport. Recently the crystal structures of the CorA Mg2+ transporter were reported. The MgtE family of Mg2+ transporters is ubiquitously distributed in all phylogenetic domains, and human homologues have been functionally characterized and suggested to be involved in magnesium homeostasis. However, the MgtE transporters have not been thoroughly characterized. Here we determine the crystal structures of the full-length Thermus thermophilus MgtE at 3.5 A resolution, and of the cytosolic domain in the presence and absence of Mg2+ at 2.3 A and 3.9 A resolutions, respectively. The transporter adopts a homodimeric architecture, consisting of the carboxy-terminal five transmembrane domains and the amino-terminal cytosolic domains, which are composed of the superhelical N domain and tandemly repeated cystathionine-beta-synthase domains. A solvent-accessible pore nearly traverses the transmembrane domains, with one potential Mg2+ bound to the conserved Asp 432 within the pore. The transmembrane (TM)5 helices from both subunits close the pore through interactions with the 'connecting helices', which connect the cystathionine-beta-synthase and transmembrane domains. Four putative Mg2+ ions are bound at the interface between the connecting helices and the other domains, and this may lock the closed conformation of the pore. A structural comparison of the two states of the cytosolic domains showed the Mg2+-dependent movement of the connecting helices, which might reorganize the transmembrane helices to open the pore. These findings suggest a homeostasis mechanism, in which Mg2+ bound between cytosolic domains regulates Mg2+ flux by sensing the intracellular Mg2+ concentration. Whether this presumed regulation controls gating of an ion channel or opening of a secondary active transporter remains to be determined.
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Affiliation(s)
- Motoyuki Hattori
- Department of Biological Information, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama-shi, Kanagawa 226-8501, Japan
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