During cotranslational processing in the rough endoplasmic reticulum, oligosaccharide chains are transferred en bloc from dolichol phosphate to certain asparagine residues of a growing polypeptide. For transfer to occur, the acceptor asparagine must be followed in sequence by:

• A Any amino acid followed by serine or threonine, except proline in the X position (Asn-X-Ser/Thr) ✓
• B Any amino acid followed by threonine (Asn-X-Thr)
• C Two consecutive lysine residues (Asn-Lys-Lys)
• D Any amino acid followed by proline (Asn-X-Pro)

Explanation

The N-linked glycosylation sequon is Asn-X-Ser/Thr, where X can be any amino acid except proline; the tripeptide must also be accessible on the luminal face of the ER. Oligosaccharyltransferase transfers the preassembled GlcNAc-rich chain from dolichol to the side-chain amide nitrogen of the asparagine. Serine and threonine acceptors define O-linked glycosylation, which proceeds residue by residue in the Golgi, not en bloc in the ER.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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