R840 alters TLR7–UNC93B1 interactions. (A) vdW and Elec interaction energies between wild-type L840 or mutant R840 and the interacting residues from UNC93B1. (B and C) (B) The π–π interaction between F843 of TLR7 and W155 of UNC93B1, and the π–cation interaction between R840 and W155, is shown on the left side panel. The black dashed lines indicate the interaction distance between W155, F843, and R840, and the solid lines (magenta and teal color) indicate the planes of the aromatic rings used to calculate the plane angle. Corresponding density plots of the interaction distances are on the right panel, and the orientation angles are plotted in the line plot (C). In the line plot, multiple lines of same color represent replicates. In the wild-type TLR7–UNC93B1 complex, L840 is positioned near F843 of TLR7 and W155 of UNC93B1. In MD simulations, L840 slightly shifts away from W155, favoring a stable π–π interaction between F843 and W155 in the wild type. In contrast, the R840 mutation forms a π–cation interaction with W155, disrupting the π–π interaction between F843 and W155, causing it to either be lost or shift into a T-shaped π–π interaction. Both ∼20° and ∼160° plane angles in the mutant indicate parallel rings; however, the rings slide and become displaced, increasing the distance between them and ultimately leading to loss of interaction.