Conserved high activity binding peptides from the Plasmodium falciparum Pf34 rhoptry protein inhibit merozoites in vitro invasion of red blood cells

* Conserved Pf34 high activity binding peptides (HABPs) interact with receptors on the RBC. * Specific binding of Pf34 HABPs is affected by enzymatic treatment of RBCs. * HABPs and mixtures of them inhibit merozoite invasion to RBCs in vitro. Rhoptries are specialized secretory organelles found in all members of the genus Plasmodium whose proteins have been considered as promising vaccine candidates due to their involvement in cell invasion and the formation of the parasitophorous vacuole (PV). The Plasmodium falciparum Pf34 protein was recently identified as a rhoptry-neck protein located in detergent-resistant microdomains (DRMs) that is expressed in mature intraerythrocytic parasite stages, but its biological function is still unknown. Receptor–ligand assays carried out in this study found that peptides 36,051 ( 101DKKFSESLKAHMDHLKILNN 120Y), 36,053 ( 141KKYIIKEIQNNKYLNKEKKS 160), 36,055 ( 181WLESVNNIEEKSNILKNIKS 200Y) and 36,056 ( 201QLLNNIASLNHTLSEEIKNI 220Y), located in the central portion of Pf34, were found to establish protease-sensitive interactions of high affinity and specificity with receptors on the surface of red blood cell (RBCs). In vitro assays showed that Pf34 high activity binding peptides (HABPs) inhibit invasion of RBCs by P. falciparum merozoites, therefore suggesting that Pf34 could act as an adhesin during invasion and supporting the inclusion of Pf34 HABPs in further studies to develop antimalarial control methods.