Mannosyl-oligosaccharide glucosidase (MOGS) (, processing ñ-glucosidase I, Glc<sub>3</sub>Man<sub>9</sub>NAc<sub>2</sub> oligosaccharide glucosidase, trimming glucosidase I, GCS1) is an enzyme with systematic name mannosyl-oligosaccharide glucohydrolase. MOGS is a transmembrane protein found in the membrane of the endoplasmic reticulum of eukaryotic cells. Biologically, it functions within the N-glycosylation pathway.
MOGS is a glycoside hydrolase enzyme, belonging to Family 63 as classified within the Carbohydrate-Active Enzyme database.
It catalyses exohydrolysis of the non-reducing terminal glucose residue in the mannosyl-oligosaccharide glycan Glc<sub>3</sub>Man<sub>9</sub>GlcNAc<sub>2</sub>.
This reaction is the first trimming step in the N-glycosylation pathway. Prior to this, the glycan was co-translationally attached to a nascent protein by the oligosaccharyltransferase complex. MOGS removes the terminal glucose residue, leaving the glycoprotein linked to Glc<sub>2</sub>Man<sub>9</sub>GlcNAc<sub>2</sub>, which can then serve as a substrate for glucosidase II.
MOGS is highly specific to the oligosaccharide in its biological substrate in the N-glycosylation pathway. Eukaryotic MOGS does not cleave simple substrates such as p-nitrophenyl glucose, and it also shows no activity to the ñ(1âÂÂ3) linkage present at the terminus of Glc<sub>1-2</sub>Man<sub>9</sub>GlcNAc<sub>2</sub>. Furthermore, the minimum substrate is the glucotriose molecule (Glc-ñ(1âÂÂ2)-Glc-ñ(1âÂÂ3)-Glc), linked as in its native Glc<sub>3</sub>Man<sub>9</sub>GlcNAc<sub>2</sub> substrate. Kojibiose, the disaccharide Glc-ñ(1âÂÂ2)-Glc, acts as a weak inhibitor on plant, animal, and yeast MOGS.
MOGS also acts to lesser extent on the corresponding glycolipids and glycopeptides.