What is mannose oligosaccharide phosphotransferase?

Mannose oligosaccharide phosphotransferase (MOP) is a type of enzyme that is involved in the post-translational modification of proteins in the endoplasmic reticulum (ER) of eukaryotic cells. This enzyme catalyzes the transfer of a phosphate group from ATP to specific mannose residues of the N-glycans (carbohydrate chains) of newly synthesized proteins. This process is called phosphorylation and it is an important step in the quality control of protein folding in the ER.

Deficiency or malfunction of MOP can cause several genetic disorders known as congenital disorders of glycosylation (CDG). These disorders are characterized by abnormal glycans on proteins, which can lead to a wide range of symptoms, including developmental delay, intellectual disability, seizures, and various organ dysfunctions.

MOP is also called as Alpha-mannosyl-oligosaccharide 1,2-N-acetylglucosaminyltransferase II (GnTII) or as Alpha-mannosidase II.