Alpha-1,6-mannosylglycoprotein 6-beta-N-acetylglucosaminyltransferase A, also known as Alpha-mannoside beta-1,6-N-acetylglucosaminyl-transferase, Mannoside acetylglucosaminyltransferase 5, N-acetylglucosaminyl-transferase V, MGAT5, and GGNT5, is a single-pass type II membrane protein that belongs to the glycosyltransferase 18 family. MGAT5 / GGNT5 catalyzes the addition of N-acetylglucosamine in beta 1-6 linkage to the alpha-linked mannose of biantennary N-linked oligosaccharides. It is one of the most important enzymes involved in the regulation of the biosynthesis of glycoprotein oligosaccharides. The central nervous system (CNS) is rich in glycoconjugates, located on the cell surface and in the extracellular matrix. MGAT5 / GGNT5 modification of complex-type N-glycans on CNS glycoproteins is involved in the regulation of depression-like behavior. Inhibitors of MGAT5 / GGNT5 might be useful in the treatment of malignancies by targeting their dependency on focal adhesion signaling for growth and metastasis.