Sialic acid-dependent binding of baculovirus-expressed recombinant antigens from Plasmodium falciparum EBA-175 to Glycophorin A

The Plasmodium falciparum Erythrocyte Binding Antigen-175. EBA-175, is a so luble merozoite stage parasite protein which binds to glycophorin A surface receptors on human erythrocytes. We have expressed two conserved cysteine- rich regions. region II and region VI, of this protein as soluble His-tagge d polypeptides in insect cell culture, and have tested their function in er ythrocyte and glycophorin A binding assays. Recombinant region II polypepti des comprised of the F2 sub-domain or the entire region II (F1 and F2 sub-d omains together) bound to erythrocytes and to purified glycophorin A in a m anner similar to the binding of native P. falciparum EBA-175 to human red c ells. Removal of sialic acid residues from the red cell surface totally abo lished recombinant region II binding, while trypsin treatment of the erythr ocyte surface reduced but did not eliminate recombinant region II binding. Synthetic peptides from three discontinuous regions of the F2 sub-domain of legion II inhibited human erythrocyte cell binding and glycophorin A recep tor recognition. Immune sera raised against EBA-175 recombinant proteins re cognized native P. falciparum-derived EBA-175. and sera from malaria-immune adults recognized recombinant antigens attesting to both the antigenicity and immunogenicity of proteins. These results: suggest that the functionall y-active recombinant region II domain of EBA-175 may be an attractive candi date for inclusion in multi-component asexual blood stage vaccines. (C) 200 1 Elsevier Science B.V.