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Cryo-EM structure of the MgtE Mg2+ channel pore domain in Mg2+-free conditions reveals cytoplasmic pore opening

By Fei Jin, Minxuan Sun, Takashi Fujii, Yurika Yamada, Jin Wang, Andres Maturana, Miki Wada, Sichen Su, Jinbiao Ma, Hironori Takeda, Tsukasa Kusakizako, Atsuhiro Tomita, Yoshiko Nakada Nakura, Kehong Liu, Tomoko Uemura, Yayoi Nomura, Norimichi Nomura, Koichi Ito, Osamu Nureki, Keiichi Namba, So Iwata, Ye Yu, Motoyuki Hattori

Posted 28 Aug 2020
bioRxiv DOI: 10.1101/2020.08.27.270991

MgtE is a Mg2+ channel conserved in organisms ranging from prokaryotes to eukaryotes, including humans, and plays an important role in Mg2+ homeostasis. The previously determined MgtE structures in the Mg2+-bound, closed state and structure-based functional analyses of MgtE revealed that the binding of Mg2+ ions to the MgtE cytoplasmic domain induces channel inactivation to maintain Mg2+ homeostasis. However, due to the lack of a structure of the MgtE channel, including its transmembrane domain in Mg2+-free conditions, the pore-opening mechanism of MgtE has remained unclear. Here, we determined the cryoelectron microscopy (cryo-EM) structure of the MgtE-Fab complex in the absence of Mg2+ ions. The Mg2+-free MgtE transmembrane domain structure and its comparison with the Mg2+-bound, closed-state structure, together with functional analyses, showed the Mg2+-dependent pore opening of MgtE on the cytoplasmic side and revealed the kink motions of the TM2 and TM5 helices at the glycine residues, which are important for channel activity. Overall, our work provides structure-based mechanistic insights into the channel gating of MgtE. ### Competing Interest Statement The authors have declared no competing interest.

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