Department of Pharmacology

Michael Maguire, Ph.D.

Maguire

Professor Emeritus, Pharmacology

Phone: (216) 368-6186
Fax: 216-368-1300
E-mail: michael.maguire@case.edu
W317A Wood Building

Research

The research in the Maguire lab is focused primarily on the structure and function of Mg²⁺ channels and transporters in bacterial metabolism and pathogenesis using primarily Salmonella enterica serovar Typhimurium (S. Typhimurium) as a model system.

CorA Mg²⁺channel, initially cloned in this laboratory, is the primary Mg²⁺ uptake system of about half of all Bacteria and Archaea. Its eukaryotic homolog is the mitochondrial Mg²⁺ channel Mrs2. CorA has no homology to any other known protein or transport system. Our recent crystal structure of CorA confirms the unique nature of CorA. This is the first crystal structure of a divalent cation channel. CorA is a homopentamer with 2 transmembrane segments per monomer. Previous data indicates that Mg²⁺ binds to CorA as a fully hydrated ion, unlike any other ion channel or transporter. We are currently using site directed mutagenesis and hydroxyl radical mapping to identify residues involved in initial binding of Mg²⁺ to CorA. Although Salmonella has two additional Mg²⁺ transporters, mutation of CorA impairs epithelial cell invasion and expression of a number of other genes important for virulence. Studies of CorA activity as a function of growth in various media strongly suggests that CorA is functionally regulated at the protein level, likely by interaction with another protein(s).The mechanism of this regulation is currently being investigated.
ZntB is a distant CorA homolog in Salmonella that mediates the efflux of Zn2+ rather than the influx of Mg²⁺. ZntB homologs are also widespread in Bacteria. We have purified ZntB and reconstituted it into liposomes to study the mechanism of transport. Preliminary data indicates that ZntB is a Zn²⁺/H⁺ antiporter. The structure of the soluble domain of ZntB has also been determined by x-ray crystallography. The overall ZntB structure is very similar to CorA. A primary question therefore is how the pathway of ion flow differs in CorA and ZntB, a question being approached by site directed mutagenesis and additional structural work.
MgtE is a Mg²⁺ channel discovered in this laboratory. It is the primary Mg²⁺ influx system for about half of the Bacteria and Archaea. A few species have both CorA and MgtE. Its eukaryotic homolog is the SLC41 family off solute carriers. The crystal structure of MgtE was recently determined by Hattori and Nureki. We are currently collaborating with them to study the sites of Mg²⁺ binding and mechanism of transport.
There are currently at least 12 identified eukaryotic Mg2+ transport systems. Mutations have been found in several of these systems that cause a variety of human disorders including electrolyte disturbances, a form of Parkinsonian dementia, spastic paraplegia and urofacial syndrome. Complete knockout of 2 systems results in early embryonic lethality. Unfortunately, there is no vertebrate model of Mg2+ homeostasis. In collaboration with Dr. Johannes von Lintig, we are developing a comprehensive vertebrate model of Mg²⁺ homeostasis. Initial work seeks to identify transcripts for each of the presumed Mg2+ systems, determine the developmental time course of their expression, and elucidate which systems are expressed in various tissues. Ultimately, we will use siRNA or gene knockout approaches to examine the phenotype(s) arising from loss of each individual system.

Current Research Directions:

Structure of CorA, ZntB and MgtE including x-ray crystallographic analysis of the full length proteins and their soluble domains. (In collaboration with Dr. Chris Dealwis and Dr. Osamu Nureki)

Regulation of CorA and ZntB ion flux by putative cytoplasmic binding proteins.

Development of the zebrafish as a model of Mg2+ homeostasis. (In collaboration with Dr. Johannes von Lintig)

Key Recent Publications:

Papp, K. and M.E. Maguire (2004) “The CorA Mg²⁺ Transporter Does Not Transport Fe²⁺,” J. Bacteriology 186:7653-7658.

Zaharik, M.L. V. L. Cullen, A. M. Fung, S. J. Libby, S. Kujat-Choy, B. Coburn, D. G. Kehres, M. E. Maguire, F. C. Fang, and B. B. Finlay (2004) The Salmonella enterica serovar Typhimurium divalent cation transport systems MntH and SitABCD are essential for virulence in an Nramp1^G169 murine typhoid model, Infection and Immunity 72:5522-5.

Lunin, V.L., E. Dobrovetsky, G. Khutoreskaya, R. Zhang, A. Joachimiak, A. Bochkarev, M.E. Maguire, A.M. Edwards, C.M. Koth (2006) “Crystal Structure of the CorA Mg²⁺ Transporter from Thermotoga maritima,” Nature 440:833-837.

Papp-Wallace, K. and M.E. Maguire (2006) “Manganese Transport and the Role of Manganese in Virulence,” Ann. Rev. Microbiol.60:187-209

Maguire, M.E. (2006) “Magnesium Transporters: Properties, Regulation and Structure”, Frontiers in Bioscience, 11:3149-3163.

Günzel, D., D.G. Kehres, L. Kucharski, M.F. Romero and M.E. Maguire (2006) “The MgtC Virulence Factor of Salmonella enterica serovar Typhimurium Activates Na⁺,K⁺-ATPase”, J. Bacteriology 188:5586-5594.

Maguire, M.E. (2006) “The Structure of CorA:A Mg²⁺-Selective Channel,” Curr. Opin. Structural Biol 16:432-438.

Papp-Wallace, K.M. and M.E. Maguire (2008) “Magnesium transport and Magnesium Homeostasis,” in EcoSal: online version of “Escherichia coli and Salmonella: Cellular and Molecular Biology,” ASM Press, Washington, D.C., http://www.ecosal.org/ecosal/index.jsp

Papp-Wallace, K.M., M. Nartea,D.G. Kehres, S. Porwollik, M. McClelland, S.J. Libby, F.C. Fang, and M.E. Maguire (2008) “The CorA Mg²⁺ channel is required for the virulence of Salmonella enterica serovar Typhimurium”, J. Bacteriology, 190:6517-6523.

Papp-Wallace, K.M. and M.E. Maguire (2008) “Regulation of the CorA Mg²⁺ channel affects the virulence of Salmonella enterica serovar Typhimurium,” J. Bacteriology, 190:6509-6516.

Moomaw, A.S. and M.E. Maguiire (2008) “The Unique Nature of Mg²⁺ Channels,” Physiology, 23:275-285.