Fig. 1: Cryo-EM structure of the bd oxidase from M. tuberculosis.
a Surface representation of the bd oxidase cryo-EM density map at 2.5 Å resolution. The bd oxidase consists of a heterodimeric CydAB core dimer The Q-loop of CydA comprises a mostly disordered QN and an ordered QC segment that are both exposed to the periplasm. b Cyt. bdMtb contains 18 membrane-spanning helices. CydA and CydB form a pseudo-symmetric dimer. All heme cofactors (b558, b595, and heme d) are located within CydA. Dashed red circles indicate the positions of accessory transmembrane helices in other bd oxidase structures. c Redox-minus-oxidized difference UV–vis spectrum of purified cyt. bdMtb. d Oxygen consumption rates from biological replicates (n = 7) of IMVs containing overproduced cytochrome bd oxidase. Control experiments were performed with IMVs from ΔcydAB cells containing an empty expression vector. Control data were obtained from biological triplicates (n = 3). All data are presented as mean values ± SD. e Triangular arrangement of the heme cofactors in CydA. f The oxygen conducting channel emerging from the membrane plane and running towards the active site. g Heme d sits in an amphipathic pocket where the hydrophilic proton channel and hydrophobic oxygen pathway converge at the dioxygen binding site. Distances between water molecules and conserved hydrophilic residues are shown. Color scheme: CydA, yellow; CydB, green; b-type hemes, purple; heme d, coral.
