trimming of second mannose on A branch

Definition

Target type: biologicalprocess

The removal of the second alpha-1,2-linked mannose from the A-chain of a glycoprotein oligosaccharide in the endoplasmic reticulum. [GOC:bf, GOC:PARL, PMID:12829701]

The trimming of the second mannose on the A branch of N-linked glycans is a crucial step in the biosynthesis of glycoproteins. This process is catalyzed by the enzyme α-mannosidase I, which specifically removes the α1,6-linked mannose residue from the Manα1,6Manα1,3Manβ1,4GlcNAc branch of the N-linked glycan. This trimming event is essential for proper protein folding, stability, and function.

The A branch of an N-linked glycan is one of the three branches attached to the core structure of the glycan. The core structure consists of three mannose residues (Manα1,6Manα1,3Manβ1,4GlcNAc2) and is linked to the asparagine residue of the protein. The A branch is the middle branch, with the B branch on the left and the C branch on the right.

The trimming of the second mannose on the A branch is a specific and regulated process. It is typically initiated in the endoplasmic reticulum (ER) and is often followed by further processing in the Golgi apparatus. α-mannosidase I is localized to the ER lumen and recognizes the specific Manα1,6Manα1,3Manβ1,4GlcNAc branch on the N-linked glycan.

Once α-mannosidase I recognizes its substrate, it cleaves the α1,6-linked mannose residue, generating a Manα1,3Manβ1,4GlcNAc structure. This trimming step is important because it alters the conformation of the glycan, making it more accessible to other glycosidases that further process the glycan in the Golgi apparatus.

The trimming of the second mannose on the A branch is a key step in the quality control of protein folding. If the protein is properly folded, it will proceed through the secretory pathway and be delivered to its final destination. However, if the protein is misfolded, it will be retained in the ER until it is properly folded or degraded. The trimming of the second mannose on the A branch is one of the signals that allows the cell to monitor the folding status of proteins.

In summary, the trimming of the second mannose on the A branch of N-linked glycans is a crucial step in the biosynthesis of glycoproteins. This process is catalyzed by the enzyme α-mannosidase I and is essential for proper protein folding, stability, and function. This specific trimming event is a key step in the quality control of protein folding, ensuring that only properly folded proteins are secreted from the cell.'
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Proteins (1)

Compounds (1)