Tubulins and microtubules are subjected to several post-translational modifications of which the reversible detyrosination/tyrosination of the carboxy-terminal end of most alpha-tubulins has been extensively analysed. This modification cycle involves a specific carboxypeptidase and the activity of the tubulin-tyrosine ligase (TTL) [2]. The true physiological function of TTL has so far not been established. Tubulin-tyrosine ligase (TTL) catalyses the ATP-dependent post-translational addition of a tyrosine to the carboxy terminal end of detyrosinated alpha-tubulin. In normally cycling cells, the tyrosinated form of tubulin predominates. However, in breast cancer cells, the detyrosinated form frequently predominates, with a correlation to tumour aggressiveness [3]. On the other hand, 3-nitrotyrosine has been shown to be incorporated, by TTL, into the carboxy terminal end of detyrosinated alpha-tubulin. This reaction is not reversible by the carboxypeptidase enzyme. Cells cultured in 3-nitrotyrosine rich medium showed evidence of altered microtubule structure and function, including altered cell morphology, epithelial barrier dysfunction, and apoptosis [4]. Bacterial homologs of TTL are predicted to form peptide tags. Some of these are fused to a 2-oxoglutarate Fe(II)-dependent dioxygenase domain [6].

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2: Tubulin-tyrosine ligase, a long-lasting enigma. Erck C, Frank R, Wehland J; Neurochem Res 2000;25:5-10. PMID:10685598

3: Tubulin detyrosination is a frequent occurrence in breast cancers of poor prognosis. Mialhe A, Lafanechere L, Treilleux I, Peloux N, Dumontet C, Bremond A, Panh MH, Payan R, Wehland J, Margolis RL, Job D; Cancer Res 2001;61:5024-5027. PMID:11431336

4: Microtubule dysfunction by posttranslational nitrotyrosination of alpha-tubulin: a nitric oxide-dependent mechanism of cellular injury. Eiserich JP, Estevez AG, Bamberg TV, Ye YZ, Chumley PH, Beckman JS, Freeman BA; Proc Natl Acad Sci U S A 1999;96:6365-6370. PMID:10339593

5: Tubulin tyrosine ligase: a shared fold with the glutathione synthetase ADP-forming family. Dideberg O, Bertrand J; Trends Biochem Sci 1998;23:57-58. PMID:9538689

6: Amidoligases with ATP-grasp, glutamine synthetase-like and acetyltransferase-like domains: synthesis of novel metabolites and peptide modifications of proteins. Iyer LM, Abhiman S, Maxwell Burroughs A, Aravind L; Mol Biosyst. 2009;5:1636-1660. PMID:20023723