C-Terminal Tail Elongation Adds a New Dimension to the Tubulin Code

Tubulin C-terminal tails undergo diverse post-translational modifications that regulate microtubule interactions with motors and severing enzymes. TTLL11, a member of the tubulin tyrosine ligase-like (TTLL) family, uniquely catalyzes glutamate addition to the terminal α-carboxyl group of both α- and β-primary tubulin tails. This linear C-terminal glutamylation enables the rescue of truncated tubulin variants and may support re-entry into the modification cycle. TTLL11 substrate specificity is determined by terminal residue identity rather than tubulin isotype. These findings expand the tubulin code and raise new questions about how linear and branched glutamylation are differentially recognized by microtubule-associated proteins.