How does an inspector call: structures of UGGT, the eukaryotic glycoprotein quality control checkpoint

In all cells derived from animals, plants, fungi and protozoa a single protein called UGGT acts as a quality control checkpoint that inspects secreted glycoproteins. UGGT has fascinated scientists for many years as it has the capacity to check the quality of a huge array of glycoproteins, which come in many different shapes and sizes and folds. The way in which it screens such a diverse group of proteins is poorly understood, and no structures exist of UGGT. Furthermore, UGGT is implicated in human diseases as it can ensure that glycoproteins from viruses (such as influenza, hepatitis C, HIV and Zika) are folded correctly. By fully characterising UGGT, it is hoped that an inhibitor could be developed that may act as a broad-spectrum anti-viral drug. Using the Macromolecular Crystallography (MX) beamlines (I02, I03, I04 and I04-1) and cryo-electron microscopy (cryo-EM) at the Electron Bio-Imaging Centre (eBIC), the structure of UGGT was solved. Four distinct crystal structures of a full-length UGGT revealed a novel seven domain fold, with four thioredoxin-like domains arranged in a long arc, which terminates in two β–sandwich domains that tightly clasp the catalytic domain. Together, the cryo-EM map, the crystal structures and the biochemical data suggested that UGGT is highly flexible, a feature which enables it to check such a wide variety of glycoproteins.