Figure 2. Comparison of closed and open structures of MscS in lipid nanodiscs.

(A) Left, the open structure of MscS in PC14:1 lipid nanodiscs (blue cartoons) is superimposed onto that of the closed state (red), previously determined in PC18:1 nanodiscs (PDB ID 6PWN, and EMD-20508). The corresponding cryo-electron microscopy (EM) density maps (transparent cyan and gray surfaces, respectively) are shown as well. Right, conformational change in each of the protomers. (B) Side-by-side comparison of the cryo-EM density maps obtained in PC18:1 (gray) and PC14:1 (cyan), alongside their overlap. The comparison highlights the reduction in the width of the transmembrane span of the channel upon opening, seemingly matched by thinning of the lipid nanodiscs, by approximately 7 Å.

Figure 2—figure supplement 1. Cryo-electron microscopy (EM) map and structural model of open-state MscS in PC14:1 lipid nanodiscs, highlighting putative sites of lipid interaction atop the C-terminus of TM2, involving residue R88.

Lipids at these sites were more clearly discerned in the closed state in PC18:1 nanodiscs (Reddy et al., 2019), and referred to as ‘hook’ lipids.