Chitobiosyldiphosphodolichol beta-mannosyltransferase

Chitobiosyldiphosphodolichol beta-mannosyltransferase is an enzyme that plays a crucial role in the process of N-linked glycosylation in eukaryotic cells. This enzyme is responsible for the transfer of a mannose residue from GDP-mannose to chitobiosyldiphosphodolichol, forming a key intermediate in the synthesis of the lipid-linked oligosaccharide precursor.

Function

Chitobiosyldiphosphodolichol beta-mannosyltransferase is involved in the early steps of the N-linked glycosylation pathway. This pathway is essential for the proper folding and function of many glycoproteins. The enzyme catalyzes the addition of a mannose residue to the growing oligosaccharide chain attached to the lipid carrier dolichol. This step is critical for the subsequent elongation and processing of the oligosaccharide precursor.

Mechanism

The enzyme uses GDP-mannose as a donor substrate and transfers the mannose residue to the chitobiosyldiphosphodolichol acceptor. The reaction occurs in the endoplasmic reticulum membrane, where the lipid-linked oligosaccharide is assembled before being transferred to nascent polypeptides.

Biological Importance

The activity of chitobiosyldiphosphodolichol beta-mannosyltransferase is essential for the proper assembly of the N-linked glycan precursor. Defects in this enzyme can lead to disorders in glycosylation, which can result in a variety of congenital disorders of glycosylation (CDGs). These disorders often have severe clinical manifestations, including developmental delays, neurological issues, and other systemic problems.

Related Enzymes

Chitobiosyldiphosphodolichol beta-mannosyltransferase is part of a larger family of glycosyltransferases that are involved in the synthesis of complex carbohydrates. Other related enzymes include:

• Dolichyl-phosphate-mannose synthase
• Oligosaccharyltransferase
• Mannosyl-oligosaccharide glucosidase

See Also

• N-linked glycosylation
• Glycosyltransferase
• Dolichol
• Endoplasmic reticulum
• Congenital disorders of glycosylation