The most abundant intracellular divalent cation, intracellular Mg concentration is tightly controlled. Work from this and other laboratories suggests Mg2+ plays a fundamental regulatory role in cellular metabolism and growth. Thus, all cells likely possess interesting mechanisms for sensing Mg2+ and for controlling its passage through the cell membrane. Moreover, Mg2+ is unique among biological cations in possessing the largest hydrated radius and the smallest atomic radius. As a consequence, in an aqueous environment, its volume change from atomic to hydrated cation is almost 400-fold, 20 times larger than that of any other common biological cation. Since it is the atomic cation that traverses the bilayer, the unique chemical properties of aqueous Mg2+ may be mirrored by unique molecular properties of Mg2+ transporters. The CorA transporter of Salmonella typhimurium represents a new family of transporters lacking significant similarity to other known proteins, yet widespread among Gram-negative bacteria. While unambiguously an integral membrane protein, 29% of CorA's 316 amino acids bear frank charge. The membrane topology of CorA shows that the protein consists of two essentially independent domains: an N-terminal periplasmic domain of about 230 amino acids and an 80 amino acid C-terminal domain comprised of only three transmembrane segments. Further, we have recently cloned a second new and again, highly unusual class of Mg2+ transporter present in both Gram-negative and Gram-positive bacteria.
Aim I will use both molecular and chemical crosslinking methods to determine if CorA functions as a homo-oligomer.
Aims II and III treat the periplasmic and membrane domains of CorA as independent structures. A model of the membrane domain will be constructed from cysteine substitution and crosslinking experiments and from site-directed mutagenesis studies to determine residues important for cation binding. The structure of the periplasmic domain will be investigated by genetic selection for mutants and by limited site-directed mutagenesis. The domain will be purified for preliminary NMR and crystallization studies. Together, data in Aims II and III will enable construction of a complete three-dimensional model of the unique CorA Mg2+ transport protein.
Aim I V will identify further new classes of Mg2+ transporters, characterize their properties and determine their phylogenetic distribution. Overall this project should lead to a greater understanding of the basis of Mg2+ transport and cellular Mg2+ homeostasis.
| Wan, Qun; Ahmad, Md Faiz; Fairman, James et al. (2011) X-ray crystallography and isothermal titration calorimetry studies of the Salmonella zinc transporter ZntB. Structure 19:700-10 |
| Moomaw, Andrea S; Maguire, Michael E (2010) Cation selectivity by the CorA Mg2+ channel requires a fully hydrated cation. Biochemistry 49:5998-6008 |
| Moomaw, Andrea S; Maguire, Michael E (2008) The unique nature of mg2+ channels. Physiology (Bethesda) 23:275-85 |
| Papp-Wallace, Krisztina M; Nartea, Margaret; Kehres, David G et al. (2008) The CorA Mg2+ channel is required for the virulence of Salmonella enterica serovar typhimurium. J Bacteriol 190:6517-23 |
| Papp-Wallace, Krisztina M; Maguire, Michael E (2008) Regulation of CorA Mg2+ channel function affects the virulence of Salmonella enterica serovar typhimurium. J Bacteriol 190:6509-16 |
| Gunzel, Dorothee; Kucharski, Lisa M; Kehres, David G et al. (2006) The MgtC virulence factor of Salmonella enterica serovar Typhimurium activates Na(+),K(+)-ATPase. J Bacteriol 188:5586-94 |
| Maguire, Michael E (2006) Magnesium transporters: properties, regulation and structure. Front Biosci 11:3149-63 |
| Maguire, Michael E (2006) The structure of CorA: a Mg(2+)-selective channel. Curr Opin Struct Biol 16:432-8 |
| Papp, Krisztina M; Maguire, Michael E (2004) The CorA Mg2+ transporter does not transport Fe2+. J Bacteriol 186:7653-8 |
| Warren, Mary Ann; Kucharski, Lisa M; Veenstra, Alexander et al. (2004) The CorA Mg2+ transporter is a homotetramer. J Bacteriol 186:4605-12 |
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