Uptake of proteins and degradation of human serum albumin by Plasmodium falciparum – infected human erythrocytes

Ahmed El Tahir,Pawan Malhotra,Virander S Chauhan

doi:10.1186/1475-2875-2-11

Abstract

BackgroundIntraerythrocytic malaria parasites actively import obligate nutrients from serum and export proteins and lipids to erythrocyte cytoplasm and membrane. The import of macromolecules in the malaria parasite has been the subject of many debates. To understand the import of macromolecules by the parasite, we studied the uptake of proteins by Plasmodium falciparum infected human erythrocyte.MethodsProteins were biotin labelled individually, purified on a gel filtration column and added to uninfected and infected asynchronized culture. The uptake of these proteins by malaria parasites was determined by western blot analysis of parasite pellet and their different fractions using streptavidin-horseradish conjugate. To further confirm this import, we studied the uptake of 125I-labelled proteins by western blot analysis as well as used direct immunofluorescence method.ResultsHere we show that biotin labelled and radio-iodinated polypeptides of molecular sizes in the range of 45 to 206 kDa, when added in the culture medium, get direct access to the parasite membrane through a membrane network by by-passing the erythrocyte cytosol. The import of these polypeptides is ATP-dependent as sodium azide treatment blocks this uptake. We also show that malaria parasites have the ability to take up and degrade biotin labelled human serum albumin, which has been shown to be essential for the parasite growth.ConclusionsThese results can be used, as a basis to explore the role of human serum albumin in the intraerythrocytic development of parasites, and this in turn can be an important adjunct to the development of novel antimalarial drugs.

Highlights

Intraerythrocytic malaria parasites actively import obligate nutrients from serum and export proteins and lipids to erythrocyte cytoplasm and membrane
We show that biotin labelled and radio-labelled proteins of different molecular weights gain access to the parasite, when added in the external medium
We extend our analysis to show that, when biotinylated human serum albumin is taken up by the parasite, it undergoes proteolysis, suggesting that the parasite has the ability to take up human serum albumin which is important for intraerythrocytic growth and differentiation

Summary

Introduction

Intraerythrocytic malaria parasites actively import obligate nutrients from serum and export proteins and lipids to erythrocyte cytoplasm and membrane. It was shown that these molecules do not cross the erythrocyte or parasitophorous vacuole membranes, but rather gain direct access from the external medium to the parasite through a duct Based on their findings, they proposed a parasitophorous duct pathway for the direct access of macromolecules through the formation of aqueous channels. The concept of direct access of macromolecules by the malaria parasite has been refuted by a number of groups who reported the inability of P. falciparum – infected erythrocytes to take up either macromolecules or small latex beads [9,10,11,12] These groups suggested that the manifestation of the duct might be due to experimental artefacts. We extend our analysis to show that, when biotinylated human serum albumin is taken up by the parasite, it undergoes proteolysis, suggesting that the parasite has the ability to take up human serum albumin which is important for intraerythrocytic growth and differentiation

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Conclusion