Abstract
The Endoplasmic Reticulum (ER) glycoprotein folding Quality Control (ERQC) machinery aids folding of glycoproteins in the ER. Misfolded glycoprotein recognition and ER-retention is mediated by the ERQC checkpoint enzyme, the 170 kDa UDP-Glucose glycoprotein glucosyltransferase (UGGT). UGGT modulation is a promising strategy for broad-spectrum antivirals, rescue-of-secretion therapy in rare disease caused by responsive mutations in glycoprotein genes, and many cancers, but to date no selective UGGT inhibitors are known. Towards the generation of selective UGGT inhibitors, we determined the crystal structures of the catalytic domain of Chaetomium thermophilum UGGT (CtUGGTGT24), alone and in complex with the inhibitor UDP-2-deoxy-2-fluoro-D-glucose (U2F). Using the CtUGGTGT24 crystals, we carried out a fragment-based lead discovery screen via X-ray crystallography and discovered that the small molecule 5-[(morpholin-4-yl)methyl]quinolin-8-ol (5M-8OH-Q) binds a CtUGGTGT24 'WY' conserved surface motif that is not present in other GT24 family glycosyltransferases. The 5M-8OH-Q molecule has a 613 μM binding affinity for human UGGT1in vitro as measured by saturation transfer difference NMR spectroscopy. The 5M-8OH-Q molecule inhibits both human UGGT1 and UGGT2 activity at concentrations higher than 750 μM in modified HEK293-6E cells. The compound is toxic in cellula and in planta at concentrations higher than 1 mM. A few off-target effects are also observed upon 5M-8OH-Q treatment. Based on an in silico model of the interaction between UGGT and its substrate N-glycan, the 5M-8OH-Q molecule likely works as a competitive inhibitor, binding to the site of recognition of the first GlcNAc residue of the substrate N-glycan.
Competing Interest Statement
The authors have declared no competing interest.
