Phosphorylation of infected erythrocyte membrane proteins in Plasmodium chabaudi

We identify phosphoproteins that are associated to the infected erythrocyte membrane of Plasmodium chabaudi. The specific antibodies that recognize the erythrocyte membrane-associated antigens, namely PcEMA1 and PcLEMA, are studied. According to sequencing analysis, neither the gene structure nor the predicted properties of these two antigens are completely distinct. The PcEMA1 is a 50 kDa acidic protein, with a pI of about 4.4, that contains 25 phosphorylation sites principally located in the repetitive sequence. Almost all of this molecule is hydrophilic. The predicted (predictment ability) of this protein is, hence, associated to the host's erythrocyte cytoskeleton and it is synthesized through an entire erythrocyte cycle. PcLEMA, instead, is a 74 kDa basic protein, with a pI of about 9.8, that contains 11 possible phosphorylation sites. This gene contains two exons: exon 1 shows transmembrane characteristics while exon 2 contains part of the hydrophilic repetitive sequences. Thus this protein is predicted as a transmembrane-associated protein and is synthesized only at the last stages of the erythrocytic cycle. In in-vitro phosphorylation experiments, both PcEMA1 and PcLEMA are phosphorylated by endogenous kinases activities. However, the degree of phosphorylation differs between the two in that PcEMA1 reveals a higher phosphorylation intensity than PcLEMA.