Ligand discovery using the inter-ligand Overhauser effect: horse liver alcohol dehydrogenase

Two dimensional nuclear Overhauser effect spectroscopy (NOESY) studies on horse liver alcohol dehydrogenase (LADH) in the presence of several ligands revealed unanticipated cross peaks arising from inter-ligand Overhasuer effects (ILOEs) connecting resonances of an inhibitor, m-methylbenzamide, and the reducing agent, cyanoborohydride, initially present to maintain NADH in the reduced state. The presence of NADH was not required to observe of these inter-ligand Overhauser effects. A model for the ternary complex was developed in which the methylbenzamide inhibitors bind to the hydrophobic pocket of the active site involved in benzyl alcohol binding, while the cyanoborohydride coordinates directly with Zn²⁺ at the active site. The observation of these effects supports the use of inter-ligand Overhauser effects for the identification of unanticipated ternary complexes that are of potential utility for the development of novel enzyme inhibitors.