Developmental modulation of protein synthetic patterns by the human malarial parasite Plasmodium falciparum

Abstract

Under conditions of in vitro culture, Plasmodium falciparum incorporated amino acids into particulate (membrane) and soluble proteins in a pattern which changed sequentially and which was dependent upon the stage of parasite maturation. Synchronized cultures pulse labeled with a mixture of 15 14C-labeled amino acids or [14C]histidine alone displayed stage-related patterns of polypeptide biosynthesis. Certain plasmodial proteins were associated with both particulate (membrane) and soluble fractions, whereas others appeared to be specific to a given fraction. Proteolysis of intact infected cells with pronase under conditions which removed 97 ± 2.2% of the endogenous red cell acetylcholinesterase activity did not cause the apparent removal of any radiolabeled proteins; this suggests the absence of externally exposed, parasite-synthesized proteins in the infected red cell membrane. Such a result was consistent whether the radiolabel was [14C]histidine or the 14C-labeled amino acid mixture. These results indicate that specific modulation of parasite biosynthetic patterns occurs during the asexual reproductive cycle and is probably one mechanism whereby parasite differentiation occurs. Despite the formation of surface excrescences on infected red cells containing mature parasites, results of surface digestion experiments failed to demonstrate the presence of surface-exposed plasmodial proteins.