Mechanistic and structural diversity between cytochrome isoforms of .

The treatment of infectious diseases caused by multidrug-resistant pathogens is a major clinical challenge of the 21st century. The membrane-embedded respiratory cytochrome -type oxygen reductase is a critical survival factor utilized by pathogenic bacteria during infection, proliferation and the transition from acute to chronic states. encodes for two cytochrome isoforms that are both involved in respiration under oxygen limited conditions. Mechanistic and structural differences between () and () operon encoded cytochrome variants have remained elusive in the past. Here, we demonstrate that cytochrome - catalyzes oxidation of benzoquinols while possessing additional specificity for naphthoquinones. Our data show that although menaquinol-1 (MK1) is not able to directly transfer electrons onto cytochrome from , it has a stimulatory effect on its oxygen reduction rate in the presence of ubiquinol-1. We further determined cryo-EM structures of cytochrome - to high resolution of 2.1 Å. Our structural insights confirm that the general architecture and substrate accessible pathways are conserved between the two oxidase isoforms, but two notable differences are apparent upon inspection: (i) does not contain a CydH-like subunit, thereby exposing heme to the membrane environment and (ii) the AppB subunit harbors a structural demethylmenaquinone-8 molecule instead of ubiquinone-8 as found in CydB of Our work completes the structural landscape of terminal respiratory oxygen reductases of and suggests that structural and functional properties of the respective oxidases are linked to quinol-pool dependent metabolic adaptations in .