ER quality control: towards an understanding at the molecular level

The process of 'quality control' in the endoplasmic reticulum (ER) involves a variety of mechanisms that collectively ensure that only correctly folde d, assembled and modified proteins are transported along the secretory path way. In contrast, nonnative proteins are retained and eventually targeted f or degradation. Recent work provides the first structural insights into the process of glycoprotein folding in the ER involving the lectin chaperones calnexin and calreticulin. Underlying principles governing the choice of ch aperone system engaged by different proteins have also been discovered.