The endoplasmic reticulum as a protein-folding compartment.

The lumen of the endoplasmic reticulum (ER) provides a dynamic and efficient environment for the folding of proteins destined for secretion and for a variety of cellular compartments and membranes. Usually, the folding process begins on the nascent chains and is completed minutes or hours later during assembly of oligomers. It is assisted by molecular chaperones and folding enzymes, some of which are unique to the ER. Quality control and selective degradation systems ensure only conformationally mature proteins are transported from the ER.