Structure-Activity Analysis of the Purine Binding Site of Human Liver Glycogen Phosphorylase

Human liver glycogen phosphorylase (HLGP) catalyzes the breakdown of glycogen to maintain serum glucose levels and is a therapeutic target for diabetes. HLGP is regulated by multiple interacting allosteric sites, each of which is a potential drug binding site. We used surface plasmon resonance (SPR) to screen for compounds that bind to the purine allosteric inhibitor site. We determined the affinities of a series of compounds and solved the crystal structures of three representative ligands with KD values from 17–550 μM. The crystal structures reveal that the affinities are partly determined by ligand-specific water-mediated hydrogen bonds and side chain movements. These effects could not be predicted; both crystallographic and SPR studies were required to understand the important features of binding and together provide a basis for the design of new allosteric inhibitors targeting this site.