An Essential Factor for High Mg2+ Tolerance of Staphylococcus aureus

Abstract

Internal bacterial concentration of Mg2+, the most abundant divalent cation in living cells, is estimated to be in the single millimolar range. However, many bacteria will thrive in media with only micromolars of Mg2+, by using a range of intensely studied and highly efficient import mechanisms, as well as in media with very high magnesium concentration, presumably mediated by currently unknown export mechanisms. Staphylococcus aureus has a particularly high Mg2+ tolerance for a pathogen, growing unimpaired in up to 770 mM Mg2+, and we here identify SA0657, a key factor in this tolerance. The predicted domain structure of SA0657 is shared with a large number of proteins in bacteria, archaea and even eukarya, for example CorB from Salmonella and the human CNNM protein family. One of the shared domains, a CBS pair potentially involved in Mg2+ sensing, contains the conserved Glycine326 which we establish to be a key residue for SA0657 function. In light of our findings, we propose the name MpfA, Magnesium Protection Factor A, for SA0657.

Sensitivity to the two peptide bacteriocin plantaricin EF is dependent on CorC, a membrane‐bound, magnesium/cobalt efflux protein

“…Heterologous expression of the LP965 and EF.A CorC proteins in L. casei also confirmed the importance of the single G334V point mutation in conferring PlnEF resistance. Because we did not find other mutants and because we were unable to construct a CorC deletion mutant in either LP965 or LP8826, our results indicate that similar to S. aureus MpfA (Armitano et al, 2016), CorC is essential for maintaining magnesium metal homeostasis in L. plantarum.…”

“…In eukaryotes, the cyclin M (CNNM) family of proteins mediate Mg 2+ transport and share some structural similarities to bacterial CorC and CorB including the C-terminal CBS pairs (Hirata, Funato, Takano, & Miki, 2014). The CBS domains of magnesium transporters are reported to be important for magnesium and ATP binding (Armitano, Redder, Guimarães, & Linder, 2016;Baykov et al, 2011). Recently, a Staphylococcus aureus protein with a domain structure similar to Salmonella CorB (magnesium protection factor A (MpfA); SA00657) was found to be essential for S. aureus growth in magnesium concentrations as low as 10 mM (Armitano et al, 2016) (Zhang et al, 2010).…”

“…The CBS domains of magnesium transporters are reported to be important for magnesium and ATP binding (Armitano, Redder, Guimarães, & Linder, 2016;Baykov et al, 2011). Recently, a Staphylococcus aureus protein with a domain structure similar to Salmonella CorB (magnesium protection factor A (MpfA); SA00657) was found to be essential for S. aureus growth in magnesium concentrations as low as 10 mM (Armitano et al, 2016) (Zhang et al, 2010). The magnesium import protein CorA has also been shown to change conformational states in response to magnesium binding (Matthies et al, 2016), thereby indicating a dynamic process.…”

CrossTalk proposal: CNNM proteins are Na+/Mg2+ exchangers playing a central role in transepithelial Mg2+ (re)absorption

“…Besides these direct measurements of [Mg 2+ ] i or total Mg levels, it was recently reported that Staphylococcus aureus with mutations in the Cnnm orthologue, MpfA , were intolerant to high levels of Mg 2+ in the culture medium (Armitano et al . ), suggesting that [Mg 2+ ] i is increased in the MpfA mutants. Taken together with the observations described in the previous paragraph, all these results support the concept that CNNM reduces intracellular Mg 2+ levels.…”

Structural Insights into the Intracellular Region of the Human Magnesium Transport Mediator CNNM4

“…There, an ATP bound Mg 2+ cation reduces the electrostatic repulsion between its polyphosphate chain and the acidic cluster. Interestingly, this acidic cluster not only appears in the CNNMs but also in other CBS-containing proteins related with Mg 2+ extrusion such as the Mg 2+ tolerance factor SA0657 found in Staphylococcus aureus [43], or bacterial proteins CorB and CorC which have been proposed to mediate Mg 2+ extrusion through bacterial Mg 2+ channel CorA [44] (Supplementary Figure S1). In other CBS-containing proteins such as the bacterial Mg 2+ channel MgtE [45,46] or the chloride channels CLCs [47], this acidic cluster is substituted by positively charged residues, which favor the interaction with the triphosphate chain of ATP.…”