Stage-specific protein synthesis by asexual blood stage parasites of Plasmodium knowlesi

Abstract

P. knowlesi parasites with a maximum age distribution of 3 h were metabolically labelled with [ 35S]methionine during 9 sequential non-overlapping intervals, from young rings to mature segmented schizonts. The proteins synthesised at the different stages were compared using sodium dodecyl sulphate-polyacrylamide gel electrophoresis; more than 40 polypeptides ( M r 20 000 to over 200 000) were identified in the different parasite preparations. The major polypeptides synthesised by rings and trophozoites of different ages were similar, but differences in minor polypeptides could always be recognised. At the onset of schizogony ring and trophozoite specific proteins ceased to be synthesised and proteins specific to schizogony emerged. In general, schizont-specific proteins were of higher molecular weight than ring stage proteins. Details of the morphological changes which occurred during the metabolic labelling episode permits correlation between parasite structure and synthesis of particular polypeptides. Comparison of parasite components metabolically labelled with [ 3H]glucosamine during defined periods of development also revealed stage-specific synthesis of glycoproteins. The extent to which proteins are altered after synthesis has been investigated by pulse-chase experiments.