THS-044 binding stabilizes the HIF2α PAS-B folded state, for regulating HIF2 activity in endogenous and clinical settings.Target: HIF2αLimited trypsin proteolysis reveals that both apo and THS-044-bound protein are efficiently cut at R330 in the extended HI loop. In the THS-044 bound state, there appears no additional proteolysis at the remaining candidate trypsin sites. In contrast, these THS-044-protected sites are protease accessible in the unliganded protein, leading its complete degradation. In parallel, NMR-based deuterium exchange measurements revealed a dramatic stabilization of the THS-044-bound protein β-sheet, with some sites experiencing 100-fold enhanced protection factors relative to the ligand-free protein. Form:Solid