26ème Congrès Général de la SFP

Microhydration of Mg2+(CH3COO–) ion pairs followed by IR laser spectroscopy: insights into the water-mediated ionic interactions in the magnesium transport channel

4 juil. 2023, 09:30

15m

Amphi Gaston Berger

Contribution orale MC13 Effets d’environnement et de solvatation sur les processus moléculaires Mini-colloques: MC13 Effets d’environnement et de solvatation sur les processus moléculaires

Orateur

Jean-Xavier BARDAUD (CNRS - ISMO)

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 ${{\mathrm{Mg}}^{2+}({\mathrm{CH}}_3{\mathrm{COO}}^{–})({\mathrm{H}}_2\mathrm{O})}_n$ 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.

Documents de présentation

Slide-SFP-Bardaud_1.pptx