Structure-Based Functional Modification Study of a Cyanobacterial Chloride Pump for Transporting Multiple Anions.

Ji-Hye Yun, Jae-Hyun Park, Zeyu Jin, Mio Ohki, Yang Wang, Cecylia Severin Lupala, Haiguang Liu, Sam-Yong Park, Weontae Lee

Journal of molecular biology 2020 Sep 04

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Understanding the structure and functional mechanisms of cyanobacterial halorhodopsin has become increasingly important, given the report that Synechocystis halorhodopsin (SyHR), a homolog of the cyanobacterial halorhodopsin from Mastigocladopsis repens (MrHR), can take up divalent ions, such as SO42-, as well as chloride ions. Here, the crystal structure of MrHR, containing a unique "TSD" chloride ion conduction motif, was determined as a homotrimer at a resolution of 1.9 Å. The detailed structure of MrHR revealed a unique trimeric topology of the light-driven chloride pump, with peculiar coordination of two water molecules and hydrogen-mediated bonds near the TSD motif, as well as a short B-C loop. Structural and functional analyses of MrHR revealed key residues responsible for the anion selectivity of cyanobacterial halorhodopsin and the involvement of two chloride ion-binding sites in the ion conduction pathway. Alanine mutant of Asn63, Pro118, and Glu182 locating in the anion inlet induce multifunctional uptake of chloride, nitrate, and sulfate ions. Moreover, the structure of N63A/P118A provides information on how SyHR promotes divalent ion transport. Our findings significantly advance the structural understanding of microbial rhodopsins with different motifs. They also provide insight into the general structural framework underlying the molecular mechanisms of the cyanobacterial chloride pump containing SyHR, the only molecule known to transport both sulfate and chloride ions. Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.

Citation

Ji-Hye Yun, Jae-Hyun Park, Zeyu Jin, Mio Ohki, Yang Wang, Cecylia Severin Lupala, Haiguang Liu, Sam-Yong Park, Weontae Lee. Structure-Based Functional Modification Study of a Cyanobacterial Chloride Pump for Transporting Multiple Anions. Journal of molecular biology. 2020 Sep 04;432(19):5273-5286