The CorA Mg2+ Transport Protein of Salmonella typhimurium

Abstract

CorA is the archetypal member of the largest family of Mgtransporters of the Bacteria and Archaea. It contains three transmembrane segments. There are no conserved charged residues within these segments indicating electrostatic interactions are not used in Mg transport through CorA. Previous mutagenesis studies of CorA revealed a single face of the third transmembrane segment that is important for Mg transport. In this study, we mutated hydroxyl-bearing and other conserved residues in the second transmembrane segment to identify residues involved in transport. Residues Ser, Thr, and Serappear to be important for transport and are oriented such that they would also line a face of an α-helix. In addition, the sequenceYGMNF, found in virtually all CorA homologues, is critical for CorA function because even conservative mutations are not tolerated at these residues. Finally, mutations of residues in the second transmembrane segment, unlike those in the third transmembrane segment, revealed cooperative behavior for the influx of Mg. We conclude that the second transmembrane segment forms a major part of the Mg pore with the third transmembrane segment of CorA.