Abstract
BackgroundBased on resistance of currently used anti-malarials, a new anti-malarial drug target against Plasmodium falciparum is urgently needed. Damaged DNA cannot be transcribed without prior DNA repair; therefore, uracil-DNA glycosylase, playing an important role in base excision repair, may act as a candidate for a new anti-malarial drug target.MethodsInitially, the native PfUDG from parasite crude extract was partially purified using two columns, and the glycosylase activity was monitored. The existence of malarial UDG activity prompted the recombinant expression of PfUDG for further characterization. The PfUDG from chloroquine and pyrimethamine resistant P. falciparum strain K1 was amplified, cloned into the expression vector, and expressed in Escherichia coli. The recombinant PfUDG was analysed by SDS-PAGE and identified by LC-MS/MS. The three dimensional structure was modelled. Biochemical properties were characterized. Inhibitory effects of 12 uracil-derivatives on PfUDG activity were investigated. Inhibition of parasite growth was determined in vitro using SYBR Green I and compared with results from human cytotoxicity tests.ResultsThe native PfUDG was partially purified with a specific activity of 1,811.7 units/mg (113.2 fold purification). After cloning of 966-bp PCR product, the 40-kDa hexa-histidine tagged PfUDG was expressed and identified. The amino acid sequence of PfUDG showed only 24.8% similarity compared with the human enzyme. The biochemical characteristics of PfUDGs were quite similar. They were inhibited by uracil glycosylase inhibitor protein as found in other organisms. Interestingly, recombinant PfUDG was inhibited by two uracil-derived compounds; 1-methoxyethyl-6-(p-n-octylanilino)uracil (IC50 of 16.75 μM) and 6-(phenylhydrazino)uracil (IC50 of 77.5 μM). Both compounds also inhibited parasite growth with IC50s of 15.6 and 12.8 μM, respectively. Moreover, 1-methoxyethyl-6-(p-n-octylanilino)uracil was not toxic to HepG2 cells, with IC50 of > 160 μM while 6-(phenylhydrazino)uracil exhibited cytoxicity, with IC50 of 27.5 μM.ConclusionsThe recombinant PfUDG was expressed, characterized and compared to partially purified native PfUDG. Their characteristics were not significantly different. PfUDG differs from human enzyme in its size and predicted amino acid sequence. Two uracil derivatives inhibited PfUDG and parasite growth; however, only one non-cytotoxic compound was found. Therefore, this selective compound can act as a lead compound for anti-malarial development in the future.
Highlights
Based on resistance of currently used anti-malarials, a new anti-malarial drug target against Plasmodium falciparum is urgently needed
Partial purification of P. falciparum UDG (PfUDG) from parasite crude extract The presence of annotated PfUDG in the Plasmodium genome suggests that P. falciparum would have DNA repair systems similar to those found in other organisms [21,22,23,24,25,26]
To address its existence and activity in P. falciparum, the native PfUDG was partially purified from parasite extract using anion exchange and Heparin Sepharose chromatography
Summary
Based on resistance of currently used anti-malarials, a new anti-malarial drug target against Plasmodium falciparum is urgently needed. Damaged DNA cannot be transcribed without prior DNA repair; uracil-DNA glycosylase, playing an important role in base excision repair, may act as a candidate for a new anti-malarial drug target. Malaria is an important infectious disease caused by Plasmodium parasites, for which Plasmodium falciparum is found prevalently and causes virulent symptoms. The most serious problem for malaria treatment is the development of resistance of the parasites to existing anti-malarial drugs including the most effective drug, artemisinin, which has been used as first-line treatment in many countries [1,2,3,4,5,6]. The discovery of new drug targets would be an effective strategy for combating multidrug resistant malaria. Very little is known about malarial DNA repair system and its significance
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