Glycoprotein folding in the endoplasmic reticulum: a tale of three chaperones?

The endoplasmic reticulum (ER) is a major site of protein synthesis and its inside, or lumen, is a major site of protein folding. The lumen of the ER contains many folding factors and molecular chaperones, which facilitate protein folding by increasing both the rate and the efficiency of this process. Amongst the many ER folding factors, there are three components that specifically modulate the folding glycoproteins bearing N-linked carbohydrate side chains. These components are calnexin, calreticulin and ERp57, and this review focuses on the molecular basis for their capacity to influence glycoprotein folding.