The structural poses of ligands that bind weakly to protein receptors are challenging to define. In this work we have studied ligand interactions with the adrenoreceptor (AR) subtypes, α1A-AR and α1B-AR, which belong to the G protein-coupled receptor (GPCR) superfamily, by employing the solution-based ligand-observed NMR method interligand NOEs for pharmacophore mapping (INPHARMA). A lack of receptor crystal structures and of subtype-selective drugs has hindered the definition of the physiological roles of each subtype and limited drug development. We determined the binding pose of the weakly binding α1A-AR-selective agonist A-61603 relative to an endogenous agonist, epinephrine, at both α1A-AR and α1B-AR. The NMR experimental data were quantitatively compared, by using SpINPHARMA, to the back-calculated spectra based on ligand poses obtained from all-atom molecular dynamics simulations. The results helped mechanistically explain the selectivity of (R)-A-61603 towards α1A-AR, thus demonstrating an approach for targeting subtype selectivity in ARs.
- G protein-coupled receptors
- interligand NOEs for pharmacophore mapping (INPHARMA)
- intermolecular ligand–ligand NOEs
- NMR spectroscopy