(a) [125I]S saturation and (b) competition binding to recombinant ACE2. (c) Schematic of ProtoArray® experimental design. (d) Positive control ProtoArray® autoradiograms showing total and non-specific (NS) binding of [3H]estradiol (E2). (e) ProtoArray® autoradiograms showing total and NS binding of [125I]S. (f, g) Representative array blocks showing total and NS [3H]E2 and [125I]S binding. Red rectangles show location of ERα proteins. (h, i) Quantification of total and NS [125I]S binding at ERα and BSA (control). Data are representative of three independent experiments. (j-l) Representative SPR sensorgrams showing kinetic and equilibrium binding analyses of immobilized S exposed to increasing concentrations of ACE2, NRP1 and ERα protein (Kon=2.03 ×105, Koff= 1.96 × 10−3, KD= 9.7 nM). In a-b, data are represented as mean ± SEM. In h, i, data are presented as median ± min and max limits.