Abstract
Magnesium is one of the most abundant metal ions in living cells. Very specific and devoted transporters have evolved for transporting Mg2+ ions across the membrane and maintain magnesium homeostasis. Using genetic screens, we were able to identify the main players in magnesium homeostasis in the opportunistic pathogen Staphylococcus aureus. Here, we show that import of magnesium relies on the redundant activity of either CorA2 or MgtE since in absence of these two importers, bacteria require increased amounts of magnesium in the medium. A third CorA-like importer seems to play a minor role, at least under laboratory conditions. For export of magnesium, we identified two proteins, MpfA and MpfB. MpfA, is the main actor since it is essential for growth in high magnesium concentrations. We show that gain of function mutations or overexpression of the minor factor, MpfB, which is part of a sigmaB controlled stress response regulon, can compensate for the absence of MpfA.
Highlights
Magnesium is ubiquitous in living cells, as it is a cofactor for hundreds of enzymes, essential for ribosome function, and interacts very strongly with nucleic acids (RNA, DNA and (d) NTPs) [1]
Magnesium is the most abundant metal ion in cells, yet to grow they still need to maintain its concentration within acceptable parameters relying on transporters capable of importing or exporting magnesium
This is essential to allow cells to strive in varying conditions, whether the environment is rich in magnesium, such as bones or kidneys, or poor in magnesium
Summary
Magnesium is ubiquitous in living cells, as it is a cofactor for hundreds of enzymes, essential for ribosome function, and interacts very strongly with nucleic acids (RNA, DNA and (d) NTPs) [1]. Magnesium is a particular ion because its radius changes drastically whether it is hydrated or not: the hydrated radius is ~400 times larger than its dehydrated one [4]. Due to this hydration, it cannot diffuse freely through the membranes meaning that magnesium transporters must be able to recognize the hydrated magnesium, remove the hydration shell and let the dehydrated magnesium enter the cell. It cannot diffuse freely through the membranes meaning that magnesium transporters must be able to recognize the hydrated magnesium, remove the hydration shell and let the dehydrated magnesium enter the cell In other words, they have to be specific for magnesium [3,5]. Genetic screens have revealed CorB and CorC in Salmonella Typhimurium, which have been described as accessory proteins to CorA [8]
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