Fig. 1.

Predictions of proton-sensing residues among all Glu and Asp in GLIC derived from electrostatic FD/DH calculations. (A) Cartoon representation of the open form of GLIC crystallized at pH 4. The front subunit is highlighted and shown in green. Asp and Glu residues predicted to have ΔpK_a larger than one unit between the open and closed states are shown as sticks and their Cα atoms are shown as red van der Waals spheres (Inset). Cα atom of R192 is shown as a cyan sphere. The black bars represent the plasma membrane level. (B) Top view of GLIC with color and representation of atoms identical to A. (C) Scatter plots for the predicted pK_a values of all Asp (19 for each subunit) and Glu (16 for each subunit) for the open and closed forms of the receptor (red crosses). Residues deviating from the diagonal by more than one pH unit (black dots) are labeled. Residues lying on the diagonal (green line) have predicted pK_a values that are equal in the two forms. The pink region contains residues for which the protonation state is predicted to change at pH₅₀ ± 1 (pH₅₀ = 5.10 ± 0.20). (D) ΔpK_a values, from the open to closed form, of Asp and Glu are plotted as a function of the residue number (red line).