Monoglycylase which modifies both tubulin and non-tubulin proteins, adding a single glycine to the gamma-carboxyl groups of specific glutamate residues to generate monoglycine side chains within the C-terminal tail of target proteins. Not involved in elongation step of the polyglycylation reaction. Preferentially monoglycylates alpha-tubulin over beta-tubulin. Together with TTLL3, mediates microtubule glycylation of primary and motile cilia, which is essential for their stability and maintenance. Together with TTLL3, glycylates sperm flagella which regulates axonemal dynein motor activity, thereby controlling flagellar beat, directional sperm swimming and male fertility. Monoglycylates non-tubulin proteins such as ANP32A, ANP32B, SET, NCL and NAP1. ATP + glycine + L-glutamyl-[protein] = ADP + glycyl-L-glutamyl-[protein] + H(+) + phosphate Two conserved structural elements specific among monoglycylases, IS1 and IS2, are involved in glycyl chains initiation. Two conserved structural interfaces likely constitute the binding platforms for tubulin tail and microtubule. Arg-360 is the main determinant for regioselectivity, which segregates between initiases and elongases in all tubulin--tyrosine ligase family. A glutamine residue at this position is found in elongases TTLL6, TTLL9, TTLL11, TTLL13, TTLL10 and favors glutamate-chain elongation, whereas an arginine residue is found in initiases TTLL2, TTLL4, TTLL5, TTLL3, TTLL8 and favors initiation. TTLL3 and TTLL8 monoglycylase-mediated glycylation of tubulin was initially reported to play a role in ependymal motile ciliary maintenance (By similarity). However, contradictory results were later observed (By similarity).