Developmentally regulated oligomerization of Plasmodium P2 protein 1 Erythrocytic stage dependent regulation of oligomerization of Plasmodium ribosomal protein P2

The eukaryotic 60S-ribosomal stalk is composed of three P ribosomal proteins (P0, P1 and P2) which associate in a pentameric structure [2P1, 2P2, P0] in the ribosome. The Plasmodium falciparum protein P2 (PfP2) appears to play non-ribosomal roles. It gets exported to the infected erythrocyte (IE) surface at 30 hrs post merozoite invasion (PMI), concomitant with extensive oligomerization. Here we present certain biophysical properties of PfP2. Recombinant P2 (rPfP2) protein showed SDS-resistant oligomerization, which could be significantly abolished under reducing conditions. However, the protein continued to oligomerize even when both the cysteine residues were mutated, and with up to 40 amino-acids (aa) deleted from the C terminal end. Gel filtration profiles of rPfP2 and mutant proteins showed anomalous migration and this anomaly was removed through the C-terminal 40 aa but not 20 aa deletion. CD analysis of rPfP2 showed largely α-helical and random coil domains. The SDS and DTT resistant oligomerization was studied further as it occurred in a development specific manner in Plasmodium. In a synchronized erythrocytic culture of P. falciparum, the PfP2 protein was detected as part of the ribosomal complex (~96 kDa) at 18 and 30 hrs PMI, and was SDS-sensitive. However, at 30 hrs, large amount of SDS-sensitive aggregates of > 600 kDa were also seen. At 30 hrs PMI, each of the parasite, IE-cytosol and IE-ghost contained 6080 kDa PfP2 complexes, which resolved to a single 65 kDa species on SDS-PAGE. Tetramethyl-rhodamine labeled rPfP2 protein exhibited DTT and SDS resistant oligomerization when treated with P. falciparum parasite extracts only from 24-36 hrs PMI, and multiple proteins seem to be required for this oligomerization. Understanding the developmental regulation of the oligomerization of PfP2 protein may help in the elucidation of the novel structure-function relationship in the export of PfP2 to the red cell surface.