The function of TTLL8 (tubulin tyrosine ligase like 8, ENSG00000138892) is as follows. 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. .