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The CorA Mg²⁺ Transporter Does Not Transport Fe²⁺

Department of Pharmacology, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio

Received 8 June 2004/ Accepted 13 August 2004

corA encodes the constitutively expressed primary Mg²⁺ uptake system of most eubacteria and many archaea. Recently, a mutation in corA was reported to make Salmonella enterica serovar Typhimurium markedly resistant to Fe²⁺-mediated toxicity. Mechanistically, this was hypothesized to be from an ability of CorA to mediate the influx of Fe²⁺. Consequently, we directly examined Fe²⁺ transport and toxicity in wild-type versus corA cells. As determined by direct transport assay, CorA cannot transport Fe²⁺ and Fe²⁺ does not potently inhibit CorA transport of ⁶³Ni²⁺. Mg²⁺ can, relatively weakly, inhibit Fe²⁺ uptake, but inhibition is not dependent on the presence of a functional corA allele. Although excess Fe²⁺ was slightly toxic to S. enterica serovar Typhimurium, we were unable to elicit a significant differential sensitivity in a wild-type versus a corA strain. We conclude that CorA does not transport Fe²⁺ and that the relationship, if any, between iron toxicity and corA is indirect.

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