Fig. 2: FasR_Δ33-C₁₄ exhibits larger protein flexibility including dimer asymmetry.

a SigmaA-weighted mF_obs-DF_calc difference Fourier map contoured at 3.5σ (green mesh) calculated with no ligand bound in the effector-binding tunnel during FasR_Δ33-C₁₄ refinement. The FasR_Δ33-C₁₄ model is shown with grey cartoons, and residues at ≤4 Å from the ligand are depicted with thin sticks. The electron density allowed to model a myristic acid, overlaid within the difference map in thick sticks coloured by atom. Note polar and charged residues on the top opening, close to the carboxyl head of the ligand. Hydrophobic residues line up the rest of the tunnel’s walls. b FasR_Δ33-C₁₄ protomers A and B are coloured as in Fig. 1. The dimer is asymmetric, quantitated by superimposing protomer B onto A (red arrow in the top panel), after what the effector-binding domains fit quite well while the HTH domains show significant rotation between one another (bottom panel), with max root-mean-square deviation (rmsd) on helices α2 and α3. c The FasR_Δ33-C₂₀-CoA and FasR_Δ33-C₁₄ structures are superposed, resulting in maximal fit on the central 4-helix bundle that mediates dimerisation (helices α8–α9 from both protomers). The upper portion of the effector-binding domains end up well aligned, but significant shifts affect the lower part together and the HTH domains (dashed arrows). The distance between the centres of mass of Tyr₇₇ on helix α3, differs by more than 10 Å between both structures. The HTH domains move consolidated with the bottom portion of juxtaposed helices α4 and α7 from the effector-binding domains.