Subunit CydX of Escherichia coli cytochrome bd ubiquinol oxidase is essential for assembly and stability of the di-heme active site

Cytochrome bd ubiquinol oxidase uses the electron transport from ubiquinol to oxygen to establish a proton gradient across the membrane. The enzyme complex consists of subunits CydA and B and contains two b- and one d-type hemes as cofactors. Recently, it was proposed that a third subunit named CydX is essential for the function of the complex. Here, we show that CydX is indeed a subunit of purified Escherichia coli cytochrome bd oxidase and that the small protein is needed either for the assembly or the stability of the active site di-heme center and, thus, is essential for oxidase activity. Structured summary of protein interactions: cydA physically interacts with cydB by affinity technology (View interaction) cydA physically interacts with cydB by molecular sieving (View interaction) cydB, cydA and cydX physically interact by molecular sieving (View interaction) cydB, cydA, and cydX physically interacts by affinity technology (1, 2) (C) 2014 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.