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A Toxoplasma gondii Leucine-Rich Repeat Protein Binds Phosphatase Type 1 Protein and Negatively Regulates Its Activity

Wassim Daher,^1, Gabrielle Oria,² Sylvain Fauquenoy,² Katia Cailliau,³ Edith Browaeys,³ Stanislas Tomavo,^2* and Jamal Khalife^1*

Unité INSERM 547/IPL, Institut Pasteur, 1 rue du Prof. Calmette, B.P. 245, 59019 Lille Cedex, France,¹ Equipe de Parasitologie Moléculaire, CNRS UMR 8576, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq Cedex, France,² UPRES EA 1033, IFR 118, SN3, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq, France³

Received 19 July 2007/ Accepted 19 July 2007

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 TgLRR1-TgPP1 interaction takes place in the nuclear subcompartment of tachyzoites. These results are consistent with those of localization studies using both indirect immunofluorescence with specific polyclonal antibody and transient transfection of T. gondii vector expressing TgLRR1 and TgPP1. The inability to obtain stable transgenic tachyzoites suggested that overexpression of TgLRR1 and TgPP1 may impair the parasite's growth. Together with the activation of Xenopus oocyte meiosis reinitiation, these data indicate that TgLRR1 protein could play a role in the regulation of the T. gondii cell cycle through the modulation of phosphatase activity.

Published ahead of print on 27 July 2007.

Present address: Department of Microbiology and Molecular Medicine, Centre Medical Universitaire, University of Geneva, 1 Rue Michel-Servet, 1211 Geneva, Switzerland.