Structural studies of Bcl-xL/ligand complexes using 19F NMR.

Fluorine atoms are often incorporated into drug molecules as part of the lead optimization process in order to improve affinity or modify undesirable metabolic and pharmacokinetic profiles. From an NMR perspective, the abundance of fluorinated drug leads provides an exploitable niche for structural studies using 19F NMR in the drug discovery process. As 19F has no interfering background signal from biological sources, 19F NMR studies of fluorinated drugs bound to their protein receptors can yield easily interpretable and unambiguous structural constraints. 19F can also be selectively incorporated into proteins to obtain additional constraints for structural studies. Despite these advantages, 19F NMR has rarely been exploited for structural studies due to its broad lines in macromolecules and their ligand complexes, leading to weak signals in 1H/19F heteronuclear NOE experiments. Here we demonstrate several different experimental strategies that use 19F NMR to obtain ligand-protein structural constraints for ligands bound to the anti-apoptotic protein Bcl-xL, a drug target for anti-cancer therapy. These examples indicate the applicability of these methods to typical structural problems encountered in the drug development process.