Plasmodium falciparum acid basic repeat antigen (ABRA) peptides: Erythrocyte binding and biological activity

Non overlapping 20-mer peptides, covering the complete sequence of acid basic repeat antigen (ABRA) of Plasmodium falciparum, were synthesised and tested in binding assays to erythrocytes. Five peptides localised in the N-terminal region coded 2148 (¹²¹LQSHKKLIKALKKNIESYQN¹⁴⁰), 2149 (¹⁴¹KKHLIYKNKSYNPLLLSCVK¹⁶⁰), 2150 (¹⁶¹KMNMLKENVDYIQKNQNLFK¹⁸⁰), 2152 (²⁰¹YKSQGHKKETSQNQNENNDN²²⁰) and 2153 (²²¹QKYQEVNDEDDVNDEEDTND²⁴⁰) specifically bind to erythrocytes. These peptides bind independently of the peptide and erythrocyte charge, with high affinity (Kd between 70 and 180 nM) and the hydrophobic interaction is important for this binding (∼30% hydrophobic critical residues). These results allow us define a specific erythrocyte binding region (residues 121-240), which may bound to at least three different binding sites on erythrocytes. Peptide 2153 shares the underlined sequence ²²¹QKYQEVNDEDDVNDEEDTND²⁴⁰ with an earlier 18-mer peptide recognised by human exposed sera. Peptides number 2148 and 2149 in vitro inhibit erythrocyte invasion by merozoites. We found that 2149 peptide and some of its glycine analogues show specific haemolytic and/or antimicrobial activity. We discuss a possible role of ABRA or its regions in the merozoite invasion of erythrocyte.