Person:

Kahne, Suzanne

Visualization of the reaction coordinate undertaken by glycosyltransferases has remained elusive, but is critical for understanding this important class of enzyme. Using substrates and substrate mimics, we describe structural snapshots of all species along the kinetic pathway for human O-GlcNAc transferase, an intracellular enzyme that catalyzes installation of a dynamic post-translational modification. The structures reveal key features of the mechanism and show that substrate participation is important during catalysis.

Gram-negative bacteria contain an unusual outer membrane that prevents the entry of most currently available antibiotics. This membrane contains a complex glycolipid, LPS, on the exterior. It is not understood how such a large molecule, which can contain hundreds of sugars and six fatty acyl chains, is transported across the cell envelope from its site of synthesis in the cytoplasmic membrane to the cell surface. Using a combination of genetics, biochemistry, and structural biology, we characterized residues in the protein that powers LPS transport to gain mechanistic insight into how ATP hydrolysis is coupled to the biological function of the transporter. These tools help us understand how to design antibiotics targeting this essential pathway.