Tubulin-tyrosine ligase (TTL) is the enzyme responsible for the reversible addition of a tyrosine residue at the carboxyl end of alpha-tubulin. TTL forms stable complexes with tubulin and inhibit tubulin polymerization. TTL is frequently suppressed during tumor progression with resulting accumulation of detyrosinated alpha-tubulin in tumor cells. TTL suppression in human cancers is associated with increased tumor aggressiveness.