To monitor the SBC-ligand binding kinetics we designed a 8luorescein labeled small molecule probe -compound 26. The 8luorescence polarization (anisotropy) of a 3-fold serial dilution of 50 µM SBC in 10 nM of the probe in 100 mM HEPES pH 7.5, 50 mM NaCl, 0.5 mM TCEP, 2% DMSO was measured to determine the KL (Supplementary Fig. ). Protein titration and the curves were 8itted using GraphPad Prism 9, using one-site 8itting models to determine the probe binding constant, KL. Samples were run in triplicate in 384 well plates, using a total volume per well of 16 μL. The bound fraction of the probe is measure using the equation: