Fig. 2. The LAX3 binding site.

a, A cut-through view of the surface presentation of LAX3 structures coloured by electrostatic potential (kT e⁻¹). From left to right: inward open, LAX3 apo; inward semi-occluded, LAX3 IAA and LAX3 2,4-D; and fully occluded, LAX3 2-NOA. b, A close-up view of the binding site. From left to right: inward open LAX3 apo; inward semi-occluded, IAA and 2,4-D; and fully occluded, 2-NOA. The dipole moments of surrounding helices are shown as well as a chemical presentation of the individual ligands. c, Density in the binding site surrounding the substrates (orange) and interacting residues (green). From left to right: inward open LAX3 apo; inward semi-occluded IAA and 2,4-D; and fully occluded 2-NOA. The map surface represents the density level at 10 standard deviations (σ) above the mean. d, Left: uptake of IAA by LAX3 point mutants into Xenopus oocytes at [³H-IAA] = 100 nM. Data are presented as mean values ± s.e.m. with n = 3 except WT where n = 12. Data analysis was performed by one-way ANOVA followed by Dunnett’s multiple-comparisons test. Right: structural overview of mutated residues from the bundle domain (green) and the scaffold domain (light purple). P values: WT versus Y242F: P = 0.0004, WT versus H247A: P < 0.0001, WT versus H247F: P = 0.0002, WT versus H319A: P = 0.0001, WT versus H319R: P = 0.0002, WT versus F326A: P = 0.0002, WT versus A327F: P = 0.0002. e, Superposition of the inward semi-occluded (IAA and 2,4-D) and fully occluded (2-NOA) LAX3 structures.