Identification and characterisation of an FK506-binding protein from Plasmodium falciparum
Citation:
Paul Monaghan, 'Identification and characterisation of an FK506-binding protein from Plasmodium falciparum', [thesis], Trinity College (Dublin, Ireland). Department of Microbiology, 2004, pp 207Abstract:
Malaria remains one of the most significant diseases worldwide. The most common and severe form of the disease is caused by Plasmodium falciparum. The need for new anti-malarial compounds has intensified in recent years as parasites continue to develop resistance to currently used drugs. It was previously shown that FK506 and rapamycin, drugs commonly used for their potent immunosuppressive activities, have activity against P. falciparum in culture. The pathway by which these drugs induce immunosuppression in humans is known to involve an FK506-binding protein (FKBP). Homologues of FKBPs have been identified in a wide variety of organisms and the fact that P. falciparum is susceptible to FK506 suggested that this organism possesses at least one member of the FKBP family. This project was undertaken to identify homologues of FKBPs in P. falciparum in an attempt to understand the mechanism by which FK506 and rapamycin exert their anti-malarial effects. The immunosuppressive properties of these compounds exclude them from consideration as anti-malarials, but such studies may facilitate the design of non-immunosuppressive analogues that retain their activity against P. falciparum. The first member of the FKBP family identified in P. falciparum was identified here by a genome sequence data-mining approach. Analysis of the derived amino acid sequence of this putative FKBP gene showed this 35-kDa protein, PfFKBP35, to be comprised of a single, N-terminal, FKBP domain and a C-terminal tripartite tetratricopeptide repeat domain. This is a strikingly similar modular structure to certain other FKBPs. However, PfFKBP35 differs from human FKBP12 at a number of key residues implicated in FK506- and rapamycin-induced immunosuppression. Analysis of the P. falciparum genome database suggested this to be the only FKBP present in the parasite. A recombinant form of PfFKBP35, like most other FKBPs, displayed peptidyl- prolyl cis-trans isomerase activity that was inhibitable by FK506 and rapamycin. Unusually, the phosphatase activity of calcineurin, the target of the FK506-FKBP12 complex in T-lymphocytes, was inhibited by PfFKBP35 independently of FK506 binding. PfFKBP35 also inhibited the thermal aggregation in vitro of two model substrates, suggesting that it has general chaperone properties. A number of non-immunosuppressive analogues of FK506 were shown to be inhibitors of parasite growth. While all compounds inhibited the chaperone activity of PfFKBP35, only some inhibited the PPIase activity, suggesting that the anti-malarial effects of this class of drug may be mediated via inhibition of the chaperone activity rather than the enzymatic activity of PfFKBP35. The potential for this class of drugs as anti-malarials was further suggested by the finding that two of the non-immunosuppressive compounds tested appear to inhibit the parasite protein while having no measurable affinity for homologous host proteins. The function of PfFKBP35 remains unknown but it may play a role in protein folding or modulation of protein function, as suggested by the observed peptidyl-prolyl cis-trans isomerase and chaperone activities. The presence of tetratricopeptide repeat motifs is suggestive of a role in intracellular protein transport. The results reported here suggest that PfFKBP35 could serve as a novel anti-malarial drug target and that compounds based on FK506 or rapamycin may have potential as anti-malarial drugs.
Author: Monaghan, Paul
Qualification name:
Doctor of Philosophy (Ph.D.)Publisher:
Trinity College (Dublin, Ireland). Department of MicrobiologyNote:
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Microbiology, Ph.D., Ph.D. Trinity College DublinMetadata
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