Monoglycylase which modifies alpha- and beta-tubulin, generating side chains of glycine on the gamma-carboxyl groups of specific glutamate residues within the C-terminal tail of alpha- and beta-tubulin. Involved in the side-chain initiation step of the glycylation reaction by adding a single glycine chain to generate monoglycine side chains. Not involved in elongation step of the polyglycylation reaction. Mainly present in locomotory and oral cilia. Cells lacking TTLL3A and TTLL3B show a strongly reduced level of monoglycylated tubulin and a moderately reduced level of polycylated tubulin. Cells lacking TTLL3A, TTLL3B, TTLL3C, TTLL3D, TTLL3E and TTLL3F display shortened axonemes that are resistant to paclitaxel, indicating that tubulin glycylation changes the lattice properties of axonemal microtubules. Axonemes are however normal at the ultrastructural level.