Pyrimidine biosynthesis represents an attractive target for chemotherapeutic intervention in the treatment of a number of diseases. The enzyme dihydroorotate dehydrogenase (DHODH), which catalyses the fourth reaction in the de novo pyrimidine .biosvnthesis pathway, has for many years received particular attention as a drug target. Human DHODH is the target of the antirheumatic drug leflunomide, and other inhibitors of this enzyme, such as brequinar, have been extensively investigated for their anticancer properties. Furthermore, the malaria parasite Plasmodium falciparum lacks the ability to salvage pyrimidines, meaning that the de novo synthesis pathway represents a potential target for the development of novel anttmalarials. Recent studies have shown that inhibitors of P. falciparum DHODH are able to suppress parasite growth in mice, validating this approach as a means of combating malaria. In this study, X-ray crystallography has been used to rationalise the inhibition patterns observed in two series of compounds that inhibit human and P. falciparum DHODHs, as well as aiding the design of inhibitors with increased potency. The best compounds from a set of human DHODH inhibitors were co-crystallised with their target enzyme, and were found to induce a small conformational change in the N-terminal helix of the enzyme that has not been observed previously. A new crystal form of PfDHODH has been discovered, leading to the determination of a 'number of eo-crystal structures at higher resolution than has been achieved by other groups. These structures reveal a subtle change in the rotamer adopted by a key arginine residue, allowing these compounds to form an additional hydrogen bond to the enzyme, relative to what has previously been reported with similar inhibitors. Virtual high-throughput screening has also been used to discover novel inhibitors of human and P. falciparum DHODHs. Biochemical assays showed a number of naphthoquinone-based compounds to be inhibitors of DHODH, and in silico docking has been used to try and explain their activity.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:578681 |
| Date | January 2011 |
| Creators | Acklam, Paul |
| Publisher | University of Leeds |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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