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Post-Translational Modifications to Toxoplasma gondii α- and β-Tubulins Include Novel C-Terminal Methylation

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posted on 04.01.2010, 00:00 by Hui Xiao, Kamal El Bissati, Pascal Verdier-Pinard, Berta Burd, Hongshan Zhang, Kami Kim, Andras Fiser, Ruth Hogue Angeletti, Louis M. Weiss
Toxoplasma gondii is an apicomplexan of both medical and veterinary importance which is classified as an NIH Category B priority pathogen. It is best known for its ability to cause congenital infection in immune competent hosts and encephalitis in immune compromised hosts. The highly stable and specialized microtubule-based cytoskeleton participates in the invasion process. The genome encodes three isoforms of both α- and β-tubulin and we show that the tubulin is extensively altered by specific post-translational modifications (PTMs) in this paper. T. gondii tubulin PTMs were analyzed by mass spectrometry and immunolabeling using specific antibodies. The PTMs identified on α-tubulin included acetylation of Lys40, removal of the last C-terminal amino acid residue Tyr453 (detyrosinated tubulin) and truncation of the last five amino acid residues. Polyglutamylation was detected on both α- and β-tubulins. An antibody directed against mammalian α-tubulin lacking the last two C-terminal residues (Δ2-tubulin) labeled the apical region of this parasite. Detyrosinated tubulin was diffusely present in subpellicular microtubules and displayed an apparent accumulation at the basal end. Methylation, a PTM not previously described on tubulin, was also detected. Methylated tubulins were not detected in the host cells, human foreskin fibroblasts, suggesting that this may be a modification specific to the Apicomplexa.