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Miner Electrolyte Metab. 1993;19(4-5):266-76.

Molecular aspects of Mg2+ transport systems.

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  • 1Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4965.


The gram-negative bacterium Salmonella typhimurium possesses three distinct Mg2+ transport systems, encoded by the CorA, MgtA, and MgtB loci. The CorA transport system is the constitutive Mg2+ influx system but can also mediate efflux at high extracellular Mg2+ concentrations. The CorA protein lacks homology to any known protein, is an integral membrane protein containing 28% percent-charged amino acids, and has three carboxyl terminal membrane-spanning segments. Its properties indicate that it is a new class of membrane transport protein, likely found in all gram-negative bacteria and possibly other organisms. In contrast, the MgtA and MgtB Mg2+ transport systems are normally expressed only at low extracellular Mg2+ concentrations and can mediate only the influx of Mg2+. Both MgtA and MgtB system are P-type ATPases; they have relatively poor homology to other known prokaryotic P-type ATPases but are highly homologous to mammalian P-type ATPases, particularly reticular Ca(2+)-ATPases. Expression of both MgtA and MgtB is highly regulated by the concentration of extracellular Mg2+. Transcription of MgtB is increased about 1,000-fold by lowering Mg2+ from 1 mM to 1 microM, and, under growth conditions of limiting Mg2+, MgtB becomes the dominant Mg2+ influx system. However, it is unclear why the cells require the use of ATP to mediate the influx of Mg2+ down its electrochemical gradient. Study of these Mg2+ transport systems should lead to further understanding of cellular Mg2+ homeostasis and eventually to characterization of eukaryotic Mg2+ transport systems.

[PubMed - indexed for MEDLINE]
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