* ~30 % of all O-linked glycans in the brain are O-mannose based. This is initiated by protein O-mannosyltransferase 1 (POMT1) and POMT 2, followed by POMGnT1 activity.
* A brain-specific β1,6-N-GlcNAcT (MGAT5B) has been cloned that transfers β1,6GlcNAc to a-mannose in GlcNAc-β1,2-Man-a sequence on both N-glycans and O-mannosyl glycans. In vivo this enzyme is dominantly considered to act on o-mannose glycans of the brain.
* Due to its activity, a variety of extended structures can be formed on the O-mannose backbone including sialylated glycans, glycans with HNK-1 epitope, and those with Lewis X structures.