The knock-down of the chloroquine resistance transporter PfCRT is linked to oligopeptide handling in Plasmodium falciparum

<p class="MsoNormal">The chloroquine resistance transporter, PfCRT, is an essential factor during intraerythrocytic development of the human malaria parasite <em>Plasmodium falciparum</em>. PfCRT resides at the digestive vacuole of the parasite, where hemoglobin taken up by the parasite from its host cell is degraded. PfCRT can acquire several mutations that render PfCRT a drug transporting system expelling compounds targeting hemoglobin degradation from the digestive vacuole. The non-drug related function of PfCRT is less clear, although a recent study has suggested a role in oligopeptide transport based on studies conducted in a heterologous expression system. The uncertainty about the natural function of PfCRT is partly due to a lack of a null mutant and a dearth of functional assays in the parasite. Here, we report on the generation of a conditional PfCRT<em> </em>knock-down mutant in <em>P. falciparum</em>. The mutant accumulated oligopeptides 2 to at least 8 residues in length under knock-down conditions, as shown by comparative global metabolomics. The accumulated oligopeptides were structurally diverse, had an isoelectric point between 4.0 and 5.4 and were electrically neutral or carried a single charge at the digestive vacuolar pH of 5.2. Fluorescently-labeled dipeptides and live cell imaging identified the digestive vacuole as the compartment where oligopeptides accumulated. Our findings suggest a function of PfCRT in oligopeptide transport across the digestive vacuolar membrane in <em>P. falciparum</em> and associated with it a role in nutrient acquisition and the maintenance of the colloid osmotic balance.</p>