17] Ligand conformations and ligand-enzyme interactions as studied by the nuclear overhauser effect

Abstract

Publisher Summary The nuclear Overhauser effect (NOE) has proved to be a powerful tool for the elucidation of molecular structure. Limitations of the NOE method for determining the conformation of a bound ligand result from the assumptions of fixed interproton distances and a single correlation time for all internuclear vectors. In many cases, the validity of these assumptions can be tested by experiment. However, if several bound conformations coexist with different interproton distances, the NOE method will yield a nonlinear average conformation skewed toward those conformations having the shortest interproton distances. Multiple conformations for the bound ligand can usually be detected by observing two or more interproton NOEs that are not mutually consistent with a single conformation. However, a major advance in biological nuclear magnetic resonance (NMR) will be the application of one- and two-dimensional isotope-filtered NOEs along with the selective labeling of the protein and ligand. This methodology will greatly increase the selectivity, identification, and resolution of the NOE experiment and thus our ability to determine the conformations and arrangements of bound ligands and the amino acid environment provided by the protein.