department of pharmacology

Maguire Laboratory Research

The research in the Maguire lab is focused on the multiple roles of Mg2+ and Mn2+ in bacterial metabolism and pathogenesis using primarily Salmonella enterica serovar Typhimurium (S. Typhimurium) as a model system.

  1. The CorA Mg2+ transporter is the primary Mg2+ uptake system of most Bacteria and Archaea. It has no homology to any other protein. We have identified features of its oligomeric structure and intramembrane residues that form an apparent Mg2+-permeable pore. Uniquely, CorA transports the charge dense Mg2+ cation without electrostatic interactions within the membrane. CorA is also a virulence factor for Salmonella typhimurium, affecting macrophage invasion and expression of a number of other genes important for virulence. Surprisingly, although S. Typhimurium has two additional Mg2+ transport systems, mutation of corA has profound metabolic defects including an inability to respire on numerous substrates including pyruvate. We are studying the role of CorA in virulence and investigation structure-function relationship of the transporter.
  2. CorA

     

  3. The MgtA/MgtB Mg2+ transporters are regulated by Mg2+, the ligand for the phoP/phoQ signal transduction system, a system essential for virulence in Salmonella and other bacteria. The MgtC protein is also regulated by phoP/phoQ. Mutations in mgtC alter S. Typhimurium virulence. Cell biology studies and expression of mgtC in frog oocytes suggests that MgtC is injected into the macrophage cell's membrane upon S. typhimurium invasion where is interacts with and constitutively activates the macrophage Na+,K+-ATPase. This results in marked alteration of macrophage membrane potential, presumably to the bacterium's benefit. Future studies will focus on transcriptional and translational regulation of mgtC to gain insight into its function.

  4. MgtA

     

  5. The MntH Mn2+ transporter is a homolog of mammalian NRAMP proteins which confer resistance to several pathogens. Most bacterial NRAMPs (MntH) are highly se¬lective Mn2+ influx systems involved in bacterial response to reactive oxygen species and pathogenesis. The SitABCD Mn2+ transporter is and ABC class protein, operative only at alkaline pH and highly selective for Mn2+. Mutation of both MntH and SitABCD renders S. Typhimurium avirulent if and only if the host organism expresses a functional NRAMP1 transporter in macrophages. We are investigating the few known Mn2+-de¬pendent enzymes for their importance in pathogenesis. One of these enzymes is GpmM, a Mn2+-dependent phosphoglyceromutase, which catalyzes an essential step in glycolysis. S. Typhimurium, like many bacteria, possesses an additional phosphogly¬ceromutase, GpmA, that is neither homologous to GpmM nor metal dependent. The capacity of these enzymes is identical, yet their mutation has profound and distinct metabolic consequences. Mutation of GpmA has no effect on the ability to grow or respire on any carbon source, but cells lacking GpmA cannot survive in stationary phase and are very sensitive to reactive oxygen species. In contrast, cells lacking GpmM has severely impaired growth on most carbon sources but are equivalent to wild type cells for stationary phase survival.

  6. MntH

     

  7. S. Typhimurium also expresses several hundred phosphoproteins. In virtually all cases, the role of phosphorylation is unknown. We have begun a proteomics project to catalog the "phosphoproteome" of S. Typhimurium, focusing (initially) on soluble phosphoproteins of the bacterium. In addition, the S. Typhimurium genome encodes 2 protein kinases and 2 protein phosphatases that are clear paralogs of eukaryotic kinases and phosphatases involved in signal transduction networks. We have cloned and partially characterized all 4 both enzymatically and phenotypically. All 4 are Mn2+ dependent and cannot use Mg2+. As part of the phosphoproteome project, we are identifying substrates of these enzymes and investigating the physiological role of phosphorylation.