Fig. 2. Rotation of the LPC headgroup.

a Relative positions of Lysolipid_1A-1B in Chamber₁ and Z_A-B. Lipid Chamber₁ is outlined in cyan dotted lines. Z_A-B are in dashed cyan and orange lines, respectively. The proposed Na⁺ binding site is highlighted by dashed purple lines. Protein rendered as surface. Lysolipids_1A-1B are in stick and sphere. b Interactions between lipid tail and LPC of Lysolipid_1A with residues in Chamber₁ and Z_A. c Interactions between lipid tail and LPC of Lysolipid_1B with residues in Chamber₁ and Z_B. b, c Carbons of lipid chamber residues are in gray. Carbons of Z-site residues are in black. Black dotted lines represent H-bonding between 2.6 Å and 3.3 Å. Red dotted lines indicate salt-bridges with distances ≤4 Å. Blue half circles indicate choline coordinating residues within 3.5 Å. Red δ indicate residues with mutations that alter activity (Table 1). Water molecule shown as small red sphere.