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Figure 1
SAXS-based screening using the volatility ratio VR, exemplified by the histidine-binding protein (HisBP) titrations. (a) 96-well plate setup for small-scale screening divided into eight twelve-point titrations, spanning from the apo ligand-less measurement to the saturated ligand-excess measurement. (b) Theoretical binding curves for a strong (blue) and weak (red) receptor–ligand interaction at constant receptor concentrations. The former reaches saturation at approximately 1:1 ratio, whereas the latter does not saturate even at 10:1 excess. (c) Example titrations of 160 µM HisBP against Arg and Orn, visualized by the buffer-subtracted SAXS intensity I(q). The apo I(q) is coloured grey, with SAXS profiles of other titration points coloured according to ligand:receptor ratios. (d) Normalized ratio R(q) versus apo protein I(q), matching equation (4)[link]. (e) Geometric average Ri for each complete Shannon channel, matching equation (6)[link]. Points have been horizontally shifted to aid visualization. (f) Computed VR curves for a preliminary titration of HisBP versus eight active and non-active amino-acids.

IUCrJ
Volume 7| Part 4| July 2020| Pages 644-655
ISSN: 2052-2525
https://doi.org/10.1107/S2052252520004169