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Eukaryotic Cell doi:10.1128/EC.00260-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A Toxoplasma gondii Leucine Rich Repeat Protein binds Phosphatase type 1 protein and negatively regulates its activity

From the Unité Inserm 547/IPL, Institut Pasteur, 1 rue du Pr Calmette, B.P. 245, 59019 Lille cedex, France, Equipe de Parasitologie Moléculaire, CNRS UMR 8576, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq Cedex, France, UPRES EA 1033, IFR 118, SN3, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq, France

^* To whom correspondence should be addressed. Email: stan.tomavo{at}univ-lille1.fr. jamal.khalife{at}pasteur-lille.fr.

	Abstract

We have characterized the Toxoplasma gondii protein phosphatase type 1, TgPP1, and a potential regulatory binding protein belonging to the Leucine Rich Repeat protein family designated TgLRR1. TgLRR1 is capable of binding to TgPP1, to inhibit its activity, and to override a G2/M cell-cycle checkpoint in Xenopus oocytes. In the parasite, TgLRR1 mRNA and protein are both highly expressed in the rapidly replicating and virulent tachyzoites while only low levels are detected in the slowly dividing and quiescent bradyzoites. TgPP1 mRNA and protein levels are equally abundant in tachyzoites and bradyzoites. Affinity-pull down and immunoprecipitation experiments reveal that the interaction TgLRR1-TgPP1 takes place in the nuclear sub-compartment of tachyzoites. These results are consistent with localization studies using both indirect immunofluorescence with specific polyclonal antibody and transient transfection of T. gondii vector expressing TgLRR1 and TgPP1. The inability of obtaining stable transgenic tachyzoites suggested that overexpression of TgLRR1 and TgPP1 may impair the parasite's growth. Together with the activation of Xenopus oocytes meiosis re-initiation, these data indicate that TgLRR1 protein could play a role in the regulation of the T. gondii cell cycle through modulation of phosphatase activity.