Enhances the tyrosine carboxypeptidase activity of VASH1 and VASH2, thereby promoting the removal of the C-terminal tyrosine residue of alpha-tubulin. Also required to enhance the solubility and secretion of VASH1 and VASH2. Plays a role in axon and excitatory synapse formation (PubMed:30607023). Interacts with VASH1 and VASH2. Detected both intracellularly and extracellularly. Within cells, localizes mainly to the apical part of the cell. Belongs to the SVBP family.