Microbial Detoxification of Superoxide: The Non-Heme Iron Reductive Paradigm for Combating Oxidative Stress

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Abstract
A reductive paradigm has emerged in recent years for detoxification of superoxide and other redox active diatomic molecules in air-sensitive bacteria and archaea. Adventitiously generated superoxide in many anaerobic or microaerophilic bacteria and archaea is scavenged by superoxide reductase (SOR) rather than the classical superoxide dismutases characteristic of aerobic microbes. SORs contain a novel five-coordinate, square-pyramidal [Fe(His)4(Cys)] ferrous active site, which adds a sixth glutamate ligand upon oxidation. This Account summarizes the recently elucidated structural and mechanistic features of SORs. The non-heme iron reductive scavenging paradigm in these air-sensitive microbes also extends to recently characterized enzymes that scavenge hydrogen peroxide and nitric oxide and to oxygen sensing proteins.