Structural modifications to a high-activity binding peptide located within the PfEMP1 NTS domain induce protection against P. falciparum malaria in Aotus monkeys

Binding of P. falciparum-infected erythrocytes to vascular enclothelium and to uninfected erythrocytes is mediated by the parasite-derived variant erythrocyte membrane protein PfEMP-1 and various receptors, both on the vascular endothelium and on the erythrocyte surface. Consecutive, non-overlapping peptides spanning the N-terminal segment (NTS) and Duffy-binding-like Pf-EMP1 sequence a-domain (DBL alpha) of this protein were tested in erythrocyte and C32 cell binding assays. Eight peptides specifically bound to C32 cells, and were named high-activity binding peptides (HABPs). No erythrocyte binding HABPs were found in this region. Strikingly, three HABPs [6504 ((1)MVELA KMGPK EAAGG DDIED20) 6505 ((21)ESAKH MFDRI GKDVY DKVKE40) and 6506 ((41)YRAKE RGKGL QGRLS EAKFEK(60))] are located within the NTS, for which no specific function has yet been described. HABP 6505 is neither immunogenic nor protection-inducing; therefore, based on our previous reports, critical amino acids (shown in bold) in HABP-C32 cell binding were identified and replaced to modify HABP immunogenicity and protectivity. Analogue peptide 12722 (ESAKH KFIDRI GKDVY DMVKE) produced high antibody titres and completely protected three out of 12 vaccinated Aotus monkeys and 23410 (KHKFD FIGKI VYDMV KER) also produced high protection-inducing titres and completely protected one out of eight monkeys. H-1 NMR studies showed that all peptides were helical. Binding of these peptides to isolated HLADR beta 1 molecules did not reveal any preference, suggesting that they could bind to molecules not studied here.