Fig. 9.

Comparative analysis of the electrostatic characteristics of the groove. a–c The electrostatic potential in the pore region of various TMEM16 constructs, obtained by solving linear Poisson-Boltzmann equation (see “Methods”) are depicted on the surface created by the [−1.0; 1.0] kcal/(mol e) range of values in the groove. The results are shown for: a TMEM16A (PDBID 5OYB); b the cryo-EM structure of L302A-nhTMEM16; and c wild-type nhTMEM16 (PDBID 4WIS). The electrostatic potential in the range of [−1.0; 1.0] kcal/(mol e)) is overlaid on the groove helices (TMs 3, 4, 6, and 7) of the respective structures. The Ca²⁺ ions are shown as purple spheres. The locations of the EC and IC vestibules are marked. d The electrostatic potential along the pore axis from the calculations shown in (a). The decreasing Z coordinate along the pore axis corresponds to EC → IC direction. The locations of selected relevant residues are marked with different symbols, with the colors specifying the TMEM16 construct as follows: Red = L302A-nhTMEM16; Blue = TMEM16A; and Green = wild-type nhTMEM16. With the respective colors, the symbols represent the following: Triangle = C_α atom of Q436 (Q637 in TMEM16A); Dot = C_α atom of Y439 (I641 in TMEM16A); and Square = Ca²⁺. e The electrostatic profile along the pore axis in the cryo-EM structure of L302A-nhTMEM16 (red thick line), and in 50 evenly spaced frames from the last 500 ns of the 2 μs MD simulation of the L302A (gray lines, see also Fig. 8). As in (b), the decreasing Z coordinate along the pore axis corresponds to EC → IC direction. The locations of selected relevant residues are marked with symbols following the same code as in (b)