Enhances the tyrosine carboxypeptidase activity of VASH1 and VASH2, thereby promoting the removal of the C-terminal tyrosine residue of alpha-tubulin (PubMed:29146869, PubMed:31171830, PubMed:31235910, PubMed:31235911, PubMed:31270470, PubMed:31324789). This activity is critical for spindle function and accurate chromosome segregation during mitosis since microtubule detyronisation regulates mitotic spindle length and postioning (PubMed:31171830). Also required to enhance the solubility and secretion of VASH1 and VASH2 (PubMed:20736312, PubMed:27879017, PubMed:30607023). Plays a role in axon and excitatory synapse formation (PubMed:31235911).