Fig. 1: Structural basis of Cx36 GJC inhibition by antimalarial drugs.

a Cryo-EM map and model of mefloquine-bound Cx36. Yellow density (top) — bound mefloquine; individual Cx36 monomers are colored white and gray; light gray density — detergent micelles. b Zoomed-in views of maps (top) and models (bottom) of the mefloquine-, quinine- and quinidine-bound Cx36 (yellow, cyan, magenta, respectively), compared to apo-Cx36 (right-most); all maps contoured at 5σ. c Densities of 6 mefloquine molecules (mesh, post-processed density map, 3σ). Inset: the planar mefloquine “body” is inserted into a hydrophobic groove between TM1 and TM2 of one Cx36 monomer and a portion of TM1 of the neighboring monomer; the head-group (“head”) orients towards the pore, making contacts with the polar region of the TM1 and with the neighboring mefloquine molecule. d A detailed representation of the binding site residues. e The drug-free (apo-Cx36) and drug-bound structures of Cx36, in surface representation, colored according to electrostatic potential (scale bar: –5/+5 kT/e). Drug binding changes pore electrostatics (mefloquine) and/or introduces a steric barrier (quinine, quinidine). f Cross-section of 6mfq–Cx36 HC. Individual Cx36 monomers are colored light and dark gray; mefloquine — yellow, POPC — light green, cholesterol — dark green, water — transparent cyan. g Average frequencies of occurrence of the contacts between Cx36 and mefloquine in the 6mfq–Cx36 MD simulations. Residues in different monomers are colored light and dark gray. Error bars represent the standard deviation. h, i Interactions established by mefloquine in cluster families C1 (h) and C2 (i). Their own frequency of occurrence during the 6mfq–Cx36 MD simulation is reported in the top right corners. The solvent-accessible surface of mefloquine is colored transparent yellow. j, k Free-energy surfaces associated with K⁺ (j) and Cl^– (k) permeation across the Cx36 hexamer in the apo-Cx36 (left) and 6mfq–Cx36 (right) systems. The maps are colored according to the right sidebars while isolines are placed every 1 kcal/mol.