Design and evaluation of antimalarial peptides derived from prediction of short linear motifs in proteins related to erythrocyte invasion

Abstract

The purpose of this study was to investigate the blood stage of the malaria causing parasite, Plasmodium falciparum, to predict potential protein interactions between the parasite merozoite and the host erythrocyte and design peptides that could interrupt these predicted interactions. We screened the P. falciparum and human proteomes for computationally predicted short linear motifs (SLiMs) in cytoplasmic portions of transmembrane proteins that could play roles in the invasion of the erythrocyte by the merozoite, an essential step in malarial pathogenesis. We tested thirteen peptides predicted to contain SLiMs, twelve of them palmitoylated to enhance membrane targeting, and found three that blocked parasite growth in culture by inhibiting the initiation of new infections in erythrocytes. Scrambled peptides for two of the most promising peptides suggested that their activity may be reflective of amino acid properties, in particular, positive charge. However, one peptide showed effects which were stronger than those of scrambled peptides. This was derived from human red blood cell glycophorin-B. We concluded that proteome-wide computational screening of the intracellular regions of both host and pathogen adhesion proteins provides potential lead peptides for the development of anti-malarial compounds.

Fig 1. Growth inhibition assay.

Peptides were tested at 100 μM. Data were collected at 48 hours (a) and at 72 hours (b). Data are means of three experiments in duplicate and vertical bars indicate standard errors.

Fig 2. Dose-response curves for selected peptides.

Peptides 5, 7, 10, 11, 12, 13 and DMSO were evaluated at 48 hours (a) and at 72 hours (b). Data are means of three experiments in duplicate and vertical bars indicate standard errors.

Fig 3. Effect of peptides on merozoite invasion.

Vehicle only control (DMSO) and peptides 5, 10 and 12 (100 μM concentration) were incubated for 2 hours with schizonts purified by magnetic selection which were subsequently introduced to fresh erythrocytes. The parasitaemia 14–16 hours later was assessed by counting rings in Giemsa stained blood smears microscopically and expressed as a percentage of the control culture (shown as % of control, y axis). Data are means of two experiments in triplicate and vertical bars indicate standard errors.

Fig 4. Growth inhibition by scrambled peptides.

Peptides 5, 10 and 12 and their scrambled peptides were tested in three concentrations, 100 μM (left bar), 10 μM (middle bar) and 1 μM (right bar) at 48 hours (a) and at 72 hours (b). Data are means of three experiments in duplicate and vertical bars indicate standard errors.