The Structure of Calnexin, an ER Chaperone Involved in Quality Control of Protein Folding

The three-dimensional structure of the lumenal domain of the lectin-like chaperone calnexin determined to 2.9 Å resolution reveals an extended 140 Å arm inserted into a β sandwich structure characteristic of legume lectins. The arm is composed of tandem repeats of two proline-rich sequence motifs which interact with one another in a head-to-tail fashion. Identification of the ligand binding site establishes calnexin as a monovalent lectin, providing insight into the mechanism by which the calnexin family of chaperones interacts with monoglucosylated glycoproteins.