Further characterization of interactions between gamete surface antigens of Plasmodium falciparum

Target antigens of malaria transmission blocking immunity include a complex of 3 gamete surface proteins of 230-kDa and 48/45-kDa glycoproteins. Previous studies have shown that epitopes recognized by blocking antibodies are conformational (reduction sensitive) in nature. Studies were conducted to characterize the interactions between the target antigens and role of disulfide groups in the formation of the complex. Treatment of detergent extracts of gametes with chaotropic agents and extremes of pH resulted in dissociation of the complex. The interaction between the 3 proteins was also perturbed when the extract was incubated in the presence of antibodies against the 230-kDa protein but not against the 48/45-kDa doublet. Chemical modifications of disulfide and sulfhydryl groups in the target antigens, otherwise inaccessible either in the total extract or after phase separation in Triton X-114, required prior denaturation of antigens.