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Ubiquinol Binding Site of Cytochrome bo3 from Escherichia coli
Structural highlights
FunctionCYOB_ECOLI Cytochrome bo(3) ubiquinol terminal oxidase is the component of the aerobic respiratory chain of E.coli that predominates when cells are grown at high aeration. Has proton pump activity across the membrane in addition to electron transfer, pumping 2 protons/electron. Protons are probably pumped via D- and K- channels found in this subunit (PubMed:11017202).[1] [2] [3] Publication Abstract from PubMedTwo independent structures of the proton-pumping, respiratory cytochrome bo(3) ubiquinol oxidase (cyt bo(3) ) have been determined by cryogenic electron microscopy (cryo-EM) in styrene-maleic acid (SMA) copolymer nanodiscs and in membrane scaffold protein (MSP) nanodiscs to 2.55- and 2.19-A resolution, respectively. The structures include the metal redox centers (heme b, heme o(3) , and Cu(B)), the redox-active cross-linked histidine-tyrosine cofactor, and the internal water molecules in the proton-conducting D channel. Each structure also contains one equivalent of ubiquinone-8 (UQ8) in the substrate binding site as well as several phospholipid molecules. The isoprene side chain of UQ8 is clamped within a hydrophobic groove in subunit I by transmembrane helix TM0, which is only present in quinol oxidases and not in the closely related cytochrome c oxidases. Both structures show carbonyl O1 of the UQ8 headgroup hydrogen bonded to D75(I) and R71(I) In both structures, residue H98(I) occupies two conformations. In conformation 1, H98(I) forms a hydrogen bond with carbonyl O4 of the UQ8 headgroup, but in conformation 2, the imidazole side chain of H98(I) has flipped to form a hydrogen bond with E14(I) at the N-terminal end of TM0. We propose that H98(I) dynamics facilitate proton transfer from ubiquinol to the periplasmic aqueous phase during oxidation of the substrate. Computational studies show that TM0 creates a channel, allowing access of water to the ubiquinol headgroup and to H98(I). Cryo-EM structures of Escherichia coli cytochrome bo(3) reveal bound phospholipids and ubiquinone-8 in a dynamic substrate binding site.,Li J, Han L, Vallese F, Ding Z, Choi SK, Hong S, Luo Y, Liu B, Chan CK, Tajkhorshid E, Zhu J, Clarke O, Zhang K, Gennis R Proc Natl Acad Sci U S A. 2021 Aug 24;118(34):e2106750118. doi: , 10.1073/pnas.2106750118. PMID:34417297[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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