Leffler, A. E. | Search bioRxiv

bioRxiv2026

State-specific binding thermodynamics predicts ligand efficacy across ion-channel families.

Predicting ligand efficacy is a critical challenge in drug discovery, as a target's functional response is often determined by the way a ligand shifts conformational equilibria between different functional states, a process that is particularly intricate in ion channels. We classify ligands based on the difference of their binding free energies on putative active and inactive conformations, calculated via free energy perturbation (FEP) for 78 protein-ligand pairs across six ion channels from four structural superfamilies: GluA2, GABAAR {rho}1, 3{beta}4 nAChR, 5-HT3AR, TRPML1, and KCNQ2. This approach accurately distinguishes agonists from antagonists across all these ion-channel families with large or subtle structural differences, including at membrane-facing sites, and enables quantitative prediction of maximum response and partial agonism. Importantly, we find that local binding-pocket conformations encode the bound ligand's efficacy even when global channel states are ambiguous. Our results demonstrate that state-specific binding thermodynamics provides a robust framework for leveraging ion channel structures of diverse conformational states to elucidate mechanisms of action and to advance ion-channel drug discovery beyond simple affinity measurements, enabling the identification of new chemical matter with desired functional attributes.

biophysics↗

bioRxiv2021

How does a small molecule bind at a cryptic binding site?

Protein-protein interactions (PPIs) are ubiquitous biomolecular processes that are central to virtually all aspects of cellular function. Identifying small molecules that modulate specific disease-related PPIs is a strategy with enormous promise for drug discovery. The design of drugs to disrupt PPIs is challenging, however, because many potential drug-binding sites at PPI interfaces are "cryptic": When unoccupied by a ligand, cryptic sites are often flat and featureless, and thus not readily recognizable in crystal structures, with the geometric and chemical characteristics of typical small-molecule binding sites only emerging upon ligand binding. The rational design of small molecules to inhibit specific PPIs would benefit from a better understanding of how such molecules bind at PPI interfaces. To this end, we have conducted unbiased, all-atom MD simulations of the binding of four small-molecule inhibitors (SP4206 and three SP4206 analogs) to interleukin 2 (IL2)--which performs its function by forming a PPI with its receptor--without incorporating any prior structural information about the ligands binding. In multiple binding events, a small molecule settled into a stable binding pose at the PPI interface of IL2, resulting in a protein-small-molecule binding site and pose virtually identical to that observed in an existing crystal structure of the IL2-SP4206 complex. Binding of the small molecule stabilized the IL2 binding groove, which when the small molecule was not bound emerged only transiently and incompletely. Moreover, free energy perturbation (FEP) calculations successfully distinguished between the native and non-native IL2-small-molecule binding poses found in the simulations, suggesting that binding simulations in combination with FEP may provide an effective tool for identifying cryptic binding sites and determining the binding poses of small molecules designed to disrupt PPI interfaces by binding to such sites.

biophysics↗