A 22 KDA PROTEIN ASSOCIATED WITH THE PLASMODIUM-FALCIPARUM MEROZOITE SURFACE PROTEIN-1 COMPLEX

The Plasmodium falciparum merozoite surface protein-1 (MSP-1) is sythe sized as a precursor of similar to 195 kDa and is processed to form a complex of polypeptides on the surface of free merozoites. As a result of a second processing event, the entire MSP-1 complex is shed from t he surface, apart from a C-terminal fragment that remains anchored to the merozoite membrane. We have identified a 22 kDa protein (p22) on t he surface of merozoites by cell surface radioiodination and indirect immunofluorescence assay on unfixed free merozoites. p22 is also a com ponent of the shed MSP-1 complex where it is present in part as a 19 k Da form (p22(19)) as shown by immunochemical and peptide mapping analy ses, The soluble complex contains MSP-1-derived polypeptides and p22 i n approximately stoichiometrically equal amounts. N-terminal amino aci d sequence analyses of p22/p22(19) showed that the protein is not deri ved from the MSP-1 precursor.