Nonheme iron proteins as an alternative system of antioxidant defense in the cells of strictly anaerobic microorganisms: A review

Enzymatic systems accounting for the relative oxygen resistance of multiple strict anaerobes are reviewed, with emphasis on molecular-biological properties and action mechanisms of nonheme iron proteins (neelaredoxins, desulfoferrodoxins, and rubrerythrins). These unique proteins, which are widespread in anaerobes, comprise a system of antioxidant defense against toxic effects of oxygen and products of its incomplete reduction (an alternative to the classic antioxidant system involving superoxide dismutase and catalase). The role of the superoxide reductase-mediated elimination of endogenous superoxide radicals is discussed. This extremely efficient means of rapid superoxide radical detoxification underlies the preferred mechanism for maintaining the optimum balance between oxidized and reduced forms of some proteins in the cells of strict anaerobes.