Plasmodium falciparumencodes a conserved active inhibitor-2 for Protein Phosphatase type 1: perspectives for novel anti-plasmodial therapy

Aline Fréville,Katia Cailliau-Maggio,Hadidjatou Kalamou,Sophia Lafitte,Jamal Khalife,Alain Martoriati,Raymond J Pierce,Christine Pierrot,Jean-François Bodart,Géraldine Tellier

doi:10.1186/1741-7007-11-80

Abstract

BackgroundIt is clear that the coordinated and reciprocal actions of kinases and phosphatases are fundamental in the regulation of development and growth of the malaria parasite. Protein Phosphatase type 1 is a key enzyme playing diverse and essential roles in cell survival. Its dephosphorylation activity/specificity is governed by the interaction of its catalytic subunit (PP1c) with regulatory proteins. Among these, inhibitor-2 (I2) is one of the most evolutionarily ancient PP1 regulators. In vivo studies in various organisms revealed a defect in chromosome segregation and cell cycle progression when the function of I2 is blocked.ResultsIn this report, we present evidence that Plasmodium falciparum, the causative agent of the most deadly form of malaria, expresses a structural homolog of mammalian I2, named PfI2. Biochemical, in vitro and in vivo studies revealed that PfI2 binds PP1 and inhibits its activity. We further showed that the motifs 12KTISW16 and 102HYNE105 are critical for PfI2 inhibitory activity. Functional studies using the Xenopus oocyte model revealed that PfI2 is able to overcome the G2/M cell cycle checkpoint by inducing germinal vesicle breakdown. Genetic manipulations in P. falciparum suggest an essential role of PfI2 as no viable mutants with a disrupted PfI2 gene were detectable. Additionally, peptides derived from PfI2 and competing with RVxF binding sites in PP1 exhibit anti-plasmodial activity against blood stage parasites in vitro.ConclusionsTaken together, our data suggest that the PfI2 protein could play a role in the regulation of the P. falciparum cell cycle through its PfPP1 phosphatase regulatory activity. Structure-activity studies of this regulator led to the identification of peptides with anti-plasmodial activity against blood stage parasites in vitro suggesting that PP1c-regulator interactions could be a novel means to control malaria.

Highlights

It is clear that the coordinated and reciprocal actions of kinases and phosphatases are fundamental in the regulation of development and growth of the malaria parasite
With respect to the endogenous regulators of PP1 and in comparison to other organisms, very few have so far been identified in P. falciparum, we previously reported the identification of two regulators, PfLRR1 and Pf inhibitor-3 [28,29]
Sequence alignment combined with visual inspection of P. falciparum Inhibitor-2 homolog (PfI2) showed an overall identity of 28% and 34% identity between amino acids at positions 5 to 105 of PfI2 when compared to human I2 (Figure 1A)

Summary

Introduction

It is clear that the coordinated and reciprocal actions of kinases and phosphatases are fundamental in the regulation of development and growth of the malaria parasite. A vast body of research has provided converging evidence that the key mechanism of the mode of action of the PP1c subunit resides in the presence of interacting regulators that direct the proper functions of this phosphatase (i.e. localization, specificity and the level of activity) [21,22,23]. The majority of regulators that inhibit the phosphatase activity interact with PP1c through an amino acid sequence present in the regulator and designated as the ‘RVxF’ motif. PfI3 strongly increased PfPP1 activity in vitro and was unable to rescue yeast deleted for the expression of its ortholog These data suggest that these regulators control PP1 activity in the nucleus and underscore the need for a better understanding of the function of PP1 regulators in each species [29]

Methods

Results

Conclusion