Induction of the proteolytic activity of a membrane protein in Plasmodium falciparum by phosphatidyl inositol-specific phospholipase C

Membrane anchoring of proteins by a covalently attached glycosyl-phosphatidylinositol moiety has been reported in many different eukaryotic cells including parasite protozoa^1-5. The diversity of proteins in which this phospholipid attachment is found suggests that it is functionally important and perhaps also functionally pleiotropic. Studies on the Thy-1 antigen of murine lymphocytes⁶ indicate that it can facilitate the lateral mobility of membrane proteins. It can also permit the rapid and specific release of the anchored proteins from the membrane following cleavage by a phosphatidyl inositol-specific phospholipase C (PI-PLC)^7,8. Here we show that this type of anchoring may be involved in the regulation of an enzymatic activity. PI-PLC releases a Plasmodium falciparum membrane protein of relative molecular mass (M_r) 76K (p76) from intact merozoites or isolated schizont membranes and induces a proteolytic activity associated with its soluble form. Endogenous activation of the proteolytic activity of p76 appears to occur at the end of the schizogony and could initiate a cascade of biochemical events associated with merozoite maturation.