Structure of a bd oxidase indicates similar mechanisms for membrane integrated oxygen reductases
Peering into a membrance oxidase Microorganisms have evolved a number of enzymes to reduce oxygen and prevent oxidative stress. Cytochrome bd oxidases serve this role and also protect pathogenic bacteria from nitric acid; however, this class of enzymes so far has eluded high resolution crystallography. Safarian et al. were able to resolve the three dimensional structure of cytochrome bd oxidase from a thermophilic bacterium (see the Perspective by Cook and Poole) The overall structure and triangular arrangement of its heme cofactors bear little structural resemblance to those of other membrane spanning oxidases, despite serving a similar function. Science, this issue p. 583; see also p. 518 Structural details reveal how pathogens protect against oxidative stress and nitric oxide. The cytochrome bd oxidases are terminal oxidases that are present in bacteria and archaea. They reduce molecular oxygen (dioxygen) to water, avoiding the production of reactive oxygen species. In addition to their contribution to the proton motive force, they mediate viability under oxygen related stress conditions and confer tolerance to nitric oxide, thus contributing to the virulence of pathogenic bacteria. Here we present the atomic structure of the bd oxidase from Geobacillus thermodenitrificans, revealing a pseudosymmetrical subunit fold. The arrangement and order of the heme cofactors support the conclusions from spectroscopic measurements that the cleavage of the dioxygen bond may be mechanistically similar to that in the heme copper containing oxidases, even though the structures are completely different.
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