Post-translational generation of constitutively active cores from larger phosphatases in the malaria parasite, Plasmodium falciparum: implications for proteomics

Table 1 Altered regulation of P. falciparum phosphatases upon processing

^aThe phosphatase assays using recombinant enzymes and ³²P-labeled phosphohistone substrate were carried out as described under Methods. The numbers represent nanomoles of ³²Pi liberated per minute per mg enzyme (protein). For calcineurin, essentially similar relative response was observed using the RII peptide as substrate (data not shown). Where indicated, the following additions were made at the indicated concentrations: Ca⁺², Mg⁺², Mn⁺² (2 mM each), calmodulin (CaM, 40 units per ml), CyP (recombinant PfCyP19, 1 μM), cyclosporin A (CsA, 1 μM), OA (0.2 μM) [30]. ^bThe full-length enzymes were purified recombinant proteins; for calcineurin, a 1:1 molar mixture of recombinant tagged PfCnA and PfCnB was used. ^cThe processed calcineurin was a 1:1 molar mixture of the 55 kDa and 16 kDa fragments of PfCnA and PfCnB, respectively, obtained after proteolytic processing (Fig. 3, 4). Similarly, the processed PfPP7 was the ~38 kDa product obtained by proteolysis of recombinant PfPP7 (Fig. 7). The activity values of the native (processed) enzymes, purified from the parasite [31, 33], were very similar to the processed recombinant enzymes and, therefore, were not shown to conserve space. Each value is a mean from three experiments with the standard error as shown.

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