Histidine-rich protein 2 of the malaria parasite, Plasmodium falciparum, is involved in detoxification of the by-products of haemoglobin degradation

The histidine-rich protein 2 (PrHRP2) of Plasmodium falciparum has been imp licated in the detoxification of ferriprotoporphyrin IX (FP) moieties that are produced as by-products of the digestion of haemoglobin. In this work, we have used a spectroscopic analysis to confirm that recombinant PfHRP2 bi nds FP. A monoclonal antibody that recognises both recombinant and authenti c PfHRP2 was used in immunofluorescence microscopy studies. We found that P fHRP2 is mainly located in the erythrocyte cytosol of infected erythrocytes , however, dual labelling studies suggest that the location of a sub-popula tion of the PfHRP2 molecules overlaps with that of the food vacuole-associa ted protein. P-glycoprotein homologue (Pgh-1), A semi-quantitative analysis of the level of PfHRP2 in infected erythrocytes suggests a concentration o f a few micromolar in the food vacuole. Under conditions designed to mimic the parasite food vacuole, we found that 1.2 muM PfHRP2 is sufficient to ca talyse the conversion of about 30%. of a 100 muM sample of FP to beta -haem atin within 24 h. Moreover, PfHRP2 is capable of promoting the H2O2-induced degradation of FP at pH 5.2. PfHRP2 also efficiently enhances the ability of FP to catalyse the H2O2-mediated oxidation of the model co-factor, ortho -phenylene diamine (OPD), These data suggest that PfHRP2 may promote the de toxification of FP and reactive oxygen species within the food vacuole. By contrast, PfHRP2 inhibits the destruction of FP by glutathione (GSH) at pH 7.4. This suggests that PfHRP2 is not a catalyst of FP degradation outside the food vacuole. (C) 2001 Elsevier Science B.V. All rights reserved.