Robust Strategy for Hit-to-Lead Discovery: NMR for SAR.

Establishing robust structure-activity relationships (SARs) is key to successful drug discovery campaigns, yet it often remains elusive due to screening and hit validation artifacts (false positives and false negatives), which frequently result in unproductive downstream expenditures of time and resources. To address this issue, we developed an integrative biophysics-driven strategy that expedites hit-to-lead discovery, mitigates false positives/negatives and common hit validation errors, and provides a robust approach to obtaining accurate binding and affinity measurements. The advantage of this method is that it vastly improves the clarity and reproducibility for affinity-driven SAR by monitoring and eliminating confounding factors.

Probing the free-state solution behavior of drugs and their tendencies to self-aggregate into nano-entities.

The free-state solution behaviors of drugs profoundly affect their properties. Therefore, it is critical to properly evaluate a drug's unique multiphase equilibrium when in an aqueous enviroment, which can comprise lone molecules, self-associating aggregate states and solid phases. To date, the full range of nano-entities that drugs can adopt has been a largely unexplored phenomenon.

Exposing Small-Molecule Nanoentities by a Nuclear Magnetic Resonance Relaxation Assay.

Small molecules can self-assemble in aqueous solution into a wide range of nanoentity types and sizes (dimers, -mers, micelles, colloids, etc.), each having their own unique properties. This has important consequences in the context of drug discovery including issues related to nonspecific binding, off-target effects, and false positives and negatives.

Mechanistic insights into allosteric regulation of the A adenosine G protein-coupled receptor by physiological cations.

Cations play key roles in regulating G-protein-coupled receptors (GPCRs), although their mechanisms are poorly understood. Here, F NMR is used to delineate the effects of cations on functional states of the adenosine A GPCR. While Na reinforces an inactive ensemble and a partial-agonist stabilized state, Ca and Mg shift the equilibrium toward active states.

Site-Specific Labeling of Protein Lysine Residues and N-Terminal Amino Groups with Indoles and Indole-Derivatives.

Indoles and indole-derivatives can be used to site-specifically label proteins on lysine and N-terminal amino groups under mild, nondenaturing reaction conditions. Hen egg white lysozyme (HEWL) and α-lactalbumin were labeled with indole, fluoroindole, or fluoroindole-2-carboxylate via electrophilic aromatic substitutions to lysine side chain Nε- and N-terminal amino imines, formed in situ in the presence of formaldehyde. The reaction is highly site-selective, easily controlled by temperature, and does not eliminate the native charge of the protein, unlike many other common lysine-specific labeling strategies.

A comparison of chemical shift sensitivity of trifluoromethyl tags: optimizing resolution in ¹⁹F NMR studies of proteins.

The elucidation of distinct protein conformers or states by fluorine ((19)F) NMR requires fluorinated moieties whose chemical shifts are most sensitive to subtle changes in the local dielectric and magnetic shielding environment. In this study we evaluate the effective chemical shift dispersion of a number of thiol-reactive trifluoromethyl probes [i.e.

¹⁹F NMR studies of a desolvated near-native protein folding intermediate.

Although many proteins are recognized to undergo folding via an intermediate, the microscopic nature of folding intermediates is less understood. In this study, ¹⁹F NMR and near-UV circular dichroism (CD) are used to characterize a transition to a thermal folding intermediate of calmodulin, a water-soluble protein, which is biosynthetically enriched with 3-fluorophenylalanine (3F-Phe). ¹⁹F NMR solvent isotope shifts, resulting from replacing H₂O with D₂O, and paramagnetic shifts arising from dissolved O₂ are used to monitor changes in the water accessibility and hydrophobicity of the protein interior as the protein progresses from a native state to an unfolded state along a heat-denaturation pathway.

Dynamic equilibria between monomeric and oligomeric misfolded states of the mammalian prion protein measured by 19F NMR.

The assembly of misfolded proteins is a critical step in the pathogenesis of amyloid and prion diseases, although the molecular mechanisms underlying this phenomenon are not completely understood. Here, we use (19)F NMR spectroscopy to examine the thermodynamic driving forces surrounding formation of β-sheet-rich oligomers early in the misfolding and aggregation pathway of the mammalian prion protein. We show that initial assembly of a small octameric intermediate is entropically driven, while further assembly to putative prefibrillar aggregates is driven by a favorable change in enthalpy.

Lysine methylation strategies for characterizing protein conformations by NMR.

In the presence of formaldehyde and a mild reducing agent, reductive methylation is known to achieve near complete dimethylation of protein amino groups under non-denaturing conditions, in aqueous media. Amino methylation of proteins is employed in mass spectrometric, crystallographic, and NMR studies. Where biosynthetic labeling is prohibitive, amino (13)C-methylation provides an attractive option for monitoring folding, kinetics, protein-protein and protein-DNA interactions by NMR.