N-glycosylation of proteins

1. N-glycans act as flags for folding and ER Quality Control. The removal of two Glc residues from the core N-oligosaccharide in the ER allows interactions with ER chaperones required for efficient folding of N-glycosylated proteins. Removing the protein from the folding environment and signalling that the protein is now deemed fit to be passed to the Golgi. 2. A core N-glycan is very large and made of hydrophilic sugars. N-glycans therefore increase protein solubility and can reduce aggregation problems during folding in the ER. 3. N-glycans are bulky and therefore constrain the α-carbon backbone of the polypeptide: they therefore influence folding rates and final protein conformation.