Orateur
Description
Ionic interactions play a crucial role in ion transport and selectivity to maintain cellular ion homeostasis. For example, the $\mathrm{Mg^{2+}}$ channel is a membrane protein that regulates $\mathrm{Mg^{2+}}$ cation concentration on both sides of the cell membrane. Crystal structure of the Magnesium Transport E channel suggests a transport mechanism for $\mathrm{Mg^{2+}}$ ions involving the motion of hexa-hydrated $\mathrm{Mg^{2+}}$ cations recognized through water-mediated ionic interactions between the $\mathrm{Mg^{2+}}$ cation and the carboxylate groups of the channel interior.$^a$
In order to characterize these water-mediated ionic interactions, we investigated $\mathrm{Mg^{2+}(CH_3COO^–)(H_2O)}_n$ clusters. We probed their structures from $n = 4$ to $17$ by measuring cryogenic gas phase infrared spectra, further interpreted by high level quantum chemistry DFT-D calculations of vibrational frequencies. This comparison allowed us to investigate size-selected micro-hydrated $\mathrm{Mg^{2+}}$ ion pairs.
In accordance with previous findings obtained on hydrated calcium$^b$ and barium$^c$ acetate clusters, hydration by 6 water molecules is insufficient to induce the ion separation. Nonetheless, partially-separated or separated ion pairs are formed from at least 10 water molecules, and more significantly with 14 water molecules. These results highlight the necessity of a second water-mediated ionic interaction for the transport of $\mathrm{Mg^{2+}}$ within the channel and possibly in cooperation with weaker secondary interactions, such as involving carbonyl groups, as suggested by the crystal structure.
$^a$Takeda, H.; Hattori, M.; Nishizawa, T.; Yamashita, K.; Shah, S. ; Caffrey, M.; Maturana, A. D.; Ishitani, R.; Nureki, O. Nat. Commun. 2014, 5374.
$^b$Denton, J. K.; Kelleher, P. J.; Johnson, M. A.; Baer, M. D.; Kathmann, S. M.; Mundy, C. J.; Wellen, R. B. A.; Allen, H. C.; Choi, T. H.; Jordan, K. D. Proc. Natl. Acad. Sci. U.S.A. 2019, 116, 14874-14880.
$^c$Donon, J.; Bardaud, J.-X.; Brenner, V.; Ishiuchi, S.; Fujii, M.; Gloaguen, E. Phys. Chem. Chem. Phys. 2022, 24, 12121-12125.
| Affiliation de l'auteur principal | CNRS ISMO |
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