trimming of terminal mannose on B branch

Definition

Target type: biologicalprocess

The removal of an alpha-1,2-linked mannose from the B-chain of a glycoprotein oligosaccharide in the endoplasmic reticulum. [GOC:bf, GOC:PARL, KEGG_REACTION:R06722, PMID:22160784]

The trimming of terminal mannose on the B branch of N-linked glycans is a critical step in the biosynthesis of glycoproteins. This process involves the sequential removal of mannose residues by specific glycosidases. The B branch refers to one of the three branches of the core N-glycan structure, which is initially assembled in the endoplasmic reticulum (ER) as a precursor oligosaccharide containing nine mannose residues.

The trimming of the B branch begins with the removal of the terminal alpha-1,6-linked mannose by the enzyme mannosidase I. This enzyme resides in the ER and specifically cleaves the alpha-1,6-linkage, leaving a mannose residue at the alpha-1,3-linked position.

Following this step, the trimmed B branch is further processed by the enzyme mannosidase II. Mannosidase II is located in the Golgi apparatus and removes the remaining terminal mannose residue on the B branch. This step is essential for the recognition of the glycan by other processing enzymes in the Golgi, such as N-acetylglucosaminyltransferases (GnTs).

The removal of terminal mannose residues from the B branch is a critical step in the quality control of glycoprotein biosynthesis. It ensures that only properly folded glycoproteins are transported to the Golgi apparatus, where they undergo further processing and sorting. The trimming process also creates recognition sites for other processing enzymes, allowing for the formation of diverse and complex glycan structures.
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Proteins (1)

Compounds (1)