TCB Publications - Abstract

Jiao Li, Long Han, Francesca Vallese, Ziqiao Ding, Sylvia K. Choi, Sangjin Hong, Yanmei Luo, Bin Liu, Chun Kit Chan, Emad Tajkhorshid, Jiapeng Zhu, Oliver Clarke, Kai Zhang, and Robert Gennis. Cryo-EM structures of Escherichia coli cytochrome bo3 reveal bound phospholipids and ubiquinone-8 in a dynamic substrate binding site. Proceedings of the National Academy of Sciences, USA, 118:e2106750118, 2021. (PMC: PMC8403832)

LI2021-ET Quinol oxidases that are members of the heme–copper superfamily of respiratory oxygen reductases have evolved from cytochrome c oxidases. They directly oxidize quinol and reduce oxygen to water. Here, we describe two high-resolution cryogenic electron microscopy structures of the proton-pumping cytochrome bo$_3$ ubiquinol oxidase in styrene– maleic acid copolymer nanodiscs and in membrane scaffold protein nanodiscs. Each structure contains one equivalent of well-resolved ubiquinone-8 in the substrate binding site as well as several phospholipid molecules. These structures indicate that H98$^I$ has two conformations that allow H98$^I$ hydrogen bonded to carbonyl O4 of the UQ8 or with E14$^I$. We propose that H98$^I$ dynamics serves to shuttle protons from ubiquinol-8 via E14$^I$ to the bulk aqueous phase upon ubiquinol-8 oxidation.

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