Parasites of the phylum Apicomplexa, including Toxoplasma gondii and Plasmodium falciparum, are major pathogens of man and domestic animals. Aspartic proteases play fundamental roles in eukaryotic biology, and have been validated as drug targets in several pathogens. The identification of the complete repertoire of seven putative aspartic protease genes in T gondii, called TgASP 1- TgASP7, was therefore undertaken, with the aim of determining the function of these proteases. The bioinformatic and phylogenetic analysis of these genes, as well as that of the putative aspartic proteases identified in the genomes of other sequenced Apicomplexa, was performed. Three of the TgASPs were selected for further study: TgASP 1, TgASP3, and TgASP5. These genes were cloned, and expressed in T gondii and in heterologous systems. The expression profiles, subcellular localizations, and post-translational modifications of these proteases are presented. The function ofTgASPl and TgASP3 was examined using traditional and conditional knock-out strategies. TgASPl localizes to punctate apical compartments in resting cells, but relocalizes dramatically to the nascent inner membrane complex of dividing cells. This protease is proposed to function in parasite replication. TgASP3 and TgASP5 localize to the trans- and cis-Golgi respectively, where they are postulated to act as maturases. Two as yet uncharacterized homologues ofTgASP3 were identified in Plasmodiumfalciparum (PfPMIX and PfPMX) and Plasmodium berghei (PbPMIX and PbPMX). These genes were cloned and expressed in different Plasmodium species. PfPMIX and PfPMX were tentatively localized to the Maurer's clefts, where they are postulated to play a role in merozoite egress from the infected red blood cell. The apparently essential roles played by several of these aspartic proteases make them attractive targets for chemotherapy.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:582543 |
| Date | January 2007 |
| Creators | Shea, Michael William |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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