Dr Megan Maher
Position: ARC Postdoctoral Fellow
Affiliation: School of Molecular and Microbial Biosciences, University of Sydney
School of Molecular and Microbial Biosciences
University of Sydney
Phone: +61 (2) 9351 3907
Fax: +61 (2) 9351 4726
My research focuses on the structural biology of metal-containing proteins, with particular emphasis on the techniques of X-ray crystallography and X-ray absorption spectroscopy.
Molybdenum-containing enzymes: Molybdenum is the only second-row transition metal that is required by most living organisms. The few species that do not require molybdenum use tungsten, which lies immediately below molybdenum on the periodic table. Because of its unique chemical versatility and unusually high bioavailability molybdenum has been incorporated into the active sites of enzymes over the course of evolution. These enzymes are found in all domains of life, participating in fundamental biological processes.
Interestingly, microbes which respire with an incredibly diverse range of substrates (such as nitrate (or nitrite), S-oxides, N-oxides, (per)chlorate, selenate, arsenate (or arsenite), dimethylsulfide and formate) all use molybdenum-containing enzymes as terminal reductases/dehydrogenases. We are particularly interested in issues of structural-based substrate specificity for this group of enzymes. To this end we are working on three molybdoenzymes: the selenate reductase from Thauera selenatis, the arsenite oxidase from the bacterium termed NT-14 and the DMS dehydrogenase from Rhodovulum sulfidophilum. Based on sequence comparisons, all three enzymes belong to the DMSO reductase family of molybdoenzymes.
We aim to solve the structure of all three enzymes by X-ray crystallography and examine the structures of their active sites in detail using X-ray absorption spectroscopy. This information will assist in understanding the structural basis of their substrate specificities and reaction mechanisms. Engineering of the selenate- and arsenite-utilizing enzymes may lead to applications in bioremediation.
Inhibition of pyrimidine synthesis (dihydroorotase): The enzyme dihydroorotase catalyses the third reaction in the pyrimidine synthesis pathway for eventual DNA and RNA production. Blockage of the pyrimidine synthesis pathway by the administration of dihydoorotase inhibitors has applications in the treatment of malaria. The malarial infection is constituted by four different Plasmodium species (P. vivax, P.ovale, P. malariae, P. falciparum), transmitted to humans through the bite of the Anopheles mosquito. The de novo pyrimidine synthesis pathway is found in both mammals and malarial parasites, but mammals are also able to produce pyrimidine nucleotides via an alternative salvage pathway. Thus, an inhibitor which blocks the de novo pathway is selectively fatal to the malarial parasite.
We are currently working on dihyhdroorotases from four sources: E. coli (the structure of which was reported by Thoden et al., 2001), B. caldolyticus, golden hamster and P. falciparum. We aim to compare the structures of these dihydroorotases in order to design inhibitors with greater specificity. To this end, we have expressed and purified the hamster and B. caldolyticus enzymes and made some progress with their crystallization. We have determined the structure of the E. coli dyhydroorotase in the presence of product, dihydroorotate and three different inhibitors. In addition, we have characterized the active site structures of these three dihydroorotases by X-ray absorption spectroscopy in the presence and absence of a transition-state analogue. The P. falciparum enzyme has been cloned and expression on the enzyme in E. coli is underway.
- Maher M. J., Santini J. M., Pickering I. J., Prince R. C., Macy J. M. and George G. N. (accepted for publication, Nov 2003)
X-ray Absorption Spectroscopy of Selenate Reductase. Inorg. Chem.
- Maher M. J., Ghosh M., Grunden A. M., Menon A. L., Adams M. W. W., Freeman H. C. and Guss J. M. (accepted for publication, Dec 2003)
Structure of the Prolidase from Pyrococcus furiosus. Biochemistry
- Maher M. J., Huang D. T. C., Guss J. M., Collyer C. A. and Christopherson R. I. (2003)
Crystallization of Hamster Dihydroorotase: Involvement of a Disulfide-Linked, Tetrameric Form. Acta Cryst., D59, 1484-1486.
- Maher M. J. and Macy J. M. (2002) Crystallization and Preliminary X-ray Analysis of the Selenate Reductase from Thauera selenatis. Acta Cryst., D58, 706-708.
- Xiao Z., Maher M. J., Cross M., Bond C. S., Guss J. M. and Wedd A. G. (2000) Mutation of the Surface Valine Residues 8 and 44 in the Rubredoxin from Clostridium pasteurianum. Solvent Access Versus Structural Changes as Determinants of Reversible Potential. J. Bioinorg. Chem., 5, 75-84.
Please see submission by Mitchell Guss
Graham George (University of Saskatchewan, Canada)