2 MAJOR PHOSPHOPROTEINS OF PLASMODIUM-FALCIPARUM ARE HEAT-SHOCK PROTEINS

Two major phosphoproteins of Plasmodium falciparum could be identified by partial amino acid sequencing as the plasmodial members of the hsp 70 heat shock protein family, Pfhsp and Pfgrp. According to phosphoamino acid analyses of Pfhsp and Pfgrp isolated from [P-32]orthophosphate-labeled malarial cultures, both proteins were phosphorylated in Ser and Thr. While Pfhsp contains higher amounts of labeled phosphoserine, Pfgrp contains higher amounts of phosphothreonine. Phosphorylation of both proteins increased throughout the entire erythrocytic growth cycle. At the trophozoite and schizont stages Pfhsp and Pfgrp are the most prominant phosphoproteins of Plasmodium falciparum. Using multiply redundant oligonucleotides directed against the N-terminus of Pfgrp we cloned and sequenced the entire Pfgrp gene. The gene encodes a product with a predicted length of 652 amino acids. The deduced amino acid sequence has identities of 65.5% and 65.0% to the human and rat grp78 proteins, respectively. Pfgrp possesses a classical N-terminal leader sequence. The published grp78 related gene sequences of Plasmodium falciparum are all fragments of the same plasmodial gene.