4.8 Article

pH-dependence of the Plasmodium falciparum chloroquine resistance transporter is linked to the transport cycle

Journal

NATURE COMMUNICATIONS
Volume 14, Issue 1, Pages -

Publisher

NATURE PORTFOLIO
DOI: 10.1038/s41467-023-39969-2

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The chloroquine resistance transporter, PfCRT, of the human malaria parasite Plasmodium falciparum is sensitive to acidic pH. Consequently, PfCRT operates at 60% of its maximal drug transport activity at the pH of 5.2 of the digestive vacuole, a proteolytic organelle from which PfCRT expels drugs interfering with heme detoxification. Here we show by alanine-scanning mutagenesis that E207 is critical for pH sensing. The E207A mutation abrogates pH-sensitivity, while preserving drug substrate specificity. Substituting E207 with Asp or His, but not other amino acids, restores pH-sensitivity. Molecular dynamics simulations and kinetics analyses suggest an allosteric binding model in which PfCRT can accept both protons and chloroquine in a partial noncompetitive manner, with increased proton concentrations decreasing drug transport. Further simulations reveal that E207 relocates from a peripheral to an engaged location during the transport cycle, forming a salt bridge with residue K80. We propose that the ionized carboxyl group of E207 acts as a hydrogen acceptor, facilitating transport cycle progression, with pH sensing as a by-product. PfCRT is a chloroquine resistance transporter from malaria parasite Plasmodium falciparum, which is sensitive to acidic pH. Here, the authors show that residue E207 is critical for pH sensing by PfCRT, using alanine-scanning mutagenesis, MD simulations and drug uptake assays.

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