Mapping of two overlapping linear epitopes in Pfg27 recognized by Plasmodium falciparum transmission-blocking monoclonal antibodies

We have reported previously the production of Plasmodium falciparum transmission-blocking monoclonal antibodies (mAb) recognizing a reduction-insensitive cross-reacting epitope in the gametocyte antigen Pfg27 and the gamete surface antigens Pfs230 and Pfs48 45. In this study, the amino acid sequence of this epitope in Pfg27 was determined. First, the epitope was localized near the N terminus of the protein by probing recombinant overlapping fragments spanning Pfg27 with transmission-blocking mAb in immunoblot experiments. The amino acid sequence of the epitope was then determined by using overlapping synthetic peptides spanning the smallest immunoreactive recombinant fragment in an ELISA. The sequence KPLDKFGNIYDYHYEH (amino acids 10-25 in the Pfg27 sequence) was shown to contain two overlapping epitopes recognized by transmission-blocking mAb. Comparison of the sequence of the gene encoding Pfg27 in seven different P. falciparum strains demonstrated that these sequential epitopes are totally conserved. Immunization of mice with synthetic peptides derived from Pfg27, conjugated with keyhole limpet hemocyanin (KLH) and formulated in Freund's adjuvant or alum, resulted in the production of antibodies capable of recognizing the peptides as well as the native Pfg27.