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Journal of Bacteriology, August 2006, p. 5586-5594, Vol. 188, No. 15
0021-9193/06/$08.00+0     doi:10.1128/JB.00296-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

The MgtC Virulence Factor of Salmonella enterica Serovar Typhimurium Activates Na+,K+-ATPase

Dorothee Günzel,1,2 Lisa M. Kucharski,2 David G. Kehres,2 Michael F. Romero,3 and Michael E. Maguire2*

Institut für klinische Physiologie, Charité-Universitätsmedizin Berlin, D-12200 Berlin, Germany,1 Department of Pharmacology,2 Department of Physiology and Biophysics, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-49653

Received 28 February 2006/ Accepted 17 May 2006

The mgtC gene of Salmonella enterica serovar Typhimurium encodes a membrane protein of unknown function that is important for full virulence in the mouse. Since mgtC is part of an operon with mgtB which encodes a Mg2+-transporting P-type ATPase, MgtC was hypothesized to function in ion transport, possibly in Mg2+ transport. Consequently, MgtC was expressed in Xenopus laevis oocytes, and its effect on ion transport was evaluated using ion selective electrodes. Oocytes expressing MgtC did not exhibit altered currents or membrane potentials in response to changes in extracellular H+, Mg2+, or Ca2+, thus ruling out a previously postulated function as a Mg2+/H+ antiporter. However, addition of extracellular K+ markedly hyperpolarized membrane potential instead of the expected depolarization. Addition of ouabain to block the oocyte Na+,K+-ATPase completely prevented hyperpolarization and restored the normal K+-induced depolarization response. These results suggested that the Na+,K+-ATPase was constitutively activated in the presence of MgtC resulting in a membrane potential largely dependent on Na+,K+-ATPase. Consistent with the involvement of Na+,K+-ATPase, oocytes expressing MgtC exhibited an increased rate of 86Rb+ uptake and had increased intracellular free [K+] and decreased free [Na+] and ATP. The free concentrations of Mg2+ and Ca2+ and cytosolic pH were unchanged, although the total intracellular Ca2+ content was slightly elevated. These results suggest that the serovar Typhimurium MgtC protein may be involved in regulating membrane potential but does not directly transport Mg2+ or another ion.

* Corresponding author. Mailing address: Department of Pharmacology, Case School of Medicine, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106-4965. Phone: (216) 368-6186. Fax: (216) 368-3395. E-mail: mem6{at}po.cwru.edu.

Journal of Bacteriology, August 2006, p. 5586-5594, Vol. 188, No. 15
0021-9193/06/$08.00+0     doi:10.1128/JB.00296-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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