Functional Characterization of Plasmodium Falciparum Pf10_0351 Protein

Abstract

Inadequate understanding of the biology of Plasmodium falciparum and the aetiology of malaria is a hindrance to the development of effective drugs and vaccines against the backdrop of resistance to Anopheles insecticides and antimalarial drugs, including artemisinin-based combination therapies (ACTs). About 60% of proteins of the P. falciparum genome has not been characterized. Since clinical symptoms of malaria are manifested at the blood stage, parasite proteins involved in erythrocyte invasion are of major research interest in vaccine development. This study aimed to functionally characterize a probable P. falciparum PF10_0351 protein, and establish its role during invasion. To achieve this, bioinformatic and immunoinformatic analyses were used to map out three highly antigenic epitopes for synthesis and antibody production. ELISA was performed to test whether the peptides will react with natural human plasma from malaria-endemic areas in Ghana with varying transmission intensities (Kintampo>Navrongo>Accra). Invasion inhibition assays were also performed to assess the ability of the peptide-specific antibodies to block invasion, using flow cytometry. Immunolocalization experiments were also performed in schizont, merozoite and gametocyte stages by immunofluorescence assay (IFA) and fluorescent microscopy. The peptides, particularly PF10_0351-2 and -3, could be recognized by naturally-induced antibodies in human plasma. However, there was no significant association between plasma antibody levels and age or parasite density by Spearman’s correlation. Peptide-specific antibodies inhibited parasite invasion of erythrocytes in a dose-dependent manner with significant differences in their invasion inhibitory effects (Tukey’s range test, p<0.0001). PF10_0351 appears to co-localize with Pfs48/45 on the surface of gametocyte stages, and also partially co-localize with MSP-1 on the surface of schizonts. Taken together, these findings suggest that the PF10_0351 protein may be localized to the surface of schizont, merozoite and gametocyte, and that it may be considered for further studies to explore its role in invasion.