 N-linked glycosylation occurs as soon as the protein sequence passes into the ER through the translocon, where it is glycosylated with a sugar molecule that forms the key ligand for the lectin molecules calreticulin (CRT; soluble in ER lumen) and calnexin (CNX; membrane bound).Favoured by the highly oxidizing environment of the ER, protein disulfide isomerases facilitate formation of disulfide bonds, which confer structural stability to the protein in order for it to withstand adverse conditions such as extremes of pH and degradative enzymes.The ER is capable of recognizing misfolding proteins without causing disruption to the functioning of the ER.