TTL (tubulin tyrosine ligase) ligates tyrosine (L-Tyr) to the carboxy terminus of the alpha-tubulin subunit of an alpha tubulin:beta tubulin dimer in an ATP-dependent reaction. The reaction mechanism has been worked out with bovine proteins, as annotated here (Deans et al. 1992), and structural studies that demonstrate the basis of the enzyme's specificity for the carboxy terminus of tubulin alpha chains have been carried out with chicken proteins (Prota et al. 2013).
tubulin-tyrosine ligase activity of TTL [cytosol]