TTL is a cytosolic enzyme involved in the posttranslational modification of alpha-tubulin (see MIM 602529). Alpha-tubulin within assembled microtubules is detyrosinated over time at the C terminus. After microtubule disassembly, TTL restores the tyrosine residues and consequently participates in a cycle of tubulin detyrosination and tyrosination (Erck et al., 2003).