Membrane-associated phosphoproteins in Plasmodium berghei-infected murine erythrocytes

Normal and Plasmodium berghei (NYU-2 strain)-infected murine erythrocytes display substantially different patterns of plasma membrane phosphoproteins phosphorylation. Intact erythrocytes (normal and parasite infected) incubated with 32Pi and isolated washed erythrocyte plasma membranes incubated with gamma-32P-ATP were analyzed for phosphoproteins by SDS PAGE and autoradiography. Two new phosphoproteins of molecular weight 45,000 (pp45) and 68,000 (pp68), which are absent in normal erythrocyte membranes, are associated with the membranes of infected erythrocytes subjected to both intact-cell and isolated-membrane phosphorylation conditions. Two-dimensional gel electrophoresis indicates that pp45 and pp68 are of parasite origin. Partial or complete proteolytic digestion reveals that pp45 is phosphorylated at similar amino acid residues both in intact cells and in isolated membranes. The pp45 phosphoprotein can be detected at as low as 3% parasitemia and its phosphorylation is not affected by 10 microM cAMP, 1 mM Ca2+, or 5 mM EGTA. Extraction of isolated washed plasma membranes with 0.5% Triton X-100 or 0.1 M NaOH indicates that pp45 is detergent insoluble and only partially extractable with NaOH, suggesting that pp45 is closely associated with the host erythrocyte plasma membrane.