Protein Phosphatase β, a Putative Type‐2A Protein Phosphatase from the Human Malaria Parasite <i>Plasmodium Falciparum</i>
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1997-10Author
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<jats:p>Protein phosphatases play a critical role in the regulation of the eukaryotic cell cycle and signal transduction. A putative protein serine/threonine phosphatase gene has been isolated from the human malaria parasite <jats:italic>Plasmodium falciparum.</jats:italic> The gene has an unusual intron that contains four repeats of 32 nucleotides and displays a high degree of size polymorphism among different strains of <jats:italic>P. falciparum.</jats:italic> The open reading frame reconstituted by removal of the intron encodes a protein of 466 amino acids with a predicted molecular mass of approximately 53.7 kDa. The encoded protein, termed protein phosphatase β (PP‐β), is composed of two distinct domains. The C‐terminal domain comprises 315 amino acids and exhibits a striking similarity to the catalytic subunits of the type‐2A protein phosphatases. Database searches revealed that the catalytic domain has the highest similarity to <jats:italic>Schiwsaccharomyces pombe</jats:italic> Ppal (58% identity and 73% similarity). However, it contains a hydrophilic insert consisting of five amino acids. The N‐terminal domain comprises 151 amino acid residues and exhibits several striking features, including high levels of charged amino acids and asparagine, and multiple consensus phosphorylation sites for a number of protein kinases. An overall structural comparison of PP‐β with other members of the protein phosphatase 2A group revealed that PP‐β is more closely related to Saccharomyces cerevisiae PPH22. Southern blots of genomic DNA digests and chromosomal separations showed that <jats:italic>PP</jats:italic>‐β is a single‐copy gene and is located on chromosome 9. A 2800‐nucleotide transcript of this gene is expressed specifically in the sexual erythrocytic stage (gametocytes). The results indicate that PP‐β may be involved in sexual stage development.</jats:p>
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