Contacts between GABA and Arg207.

<p>(A) The average number of contacts between GABA and Arg207 are shown for the BIND (red), PARTIAL (orange) and NEARBY (green) categories as a function of their distance from the binding site COM. The red dashed line indicates the distance at which the GABA molecules enter the electrostatic field. This is visually depicted (A–inset), showing the net dipoles on the GABA molecules relative to the position of Arg207. (B) Analysis of Arg207 rotamers. The nine possible rotamers formed by the N-CA-CB-CG (χ₁ dihedral) and CB-CG-CD-NE (χ₁ dihedral) dihedrals of Arg207 were analyzed in terms of their distance to the average GABA position (for the bin when GABA is 2 nm from the binding site). These distances were calculated and standardized for each rotamer during all of the NEARBY simulations. This shows that the conformation of rotamer #3 allows Arg207 to get significantly closer to GABA than any other rotamer. This is illustrated by a visual comparison between rotamer #3 and rotamer #4 (B–inset, where the position of GABA is represented by an olive green sphere). (C) The percentage population of Arg207 rotamers for each simulation category was calculated as function of the GABA distance from the binding site. This shows that in the NEARBY simulations, Arg207 occupies rotamer #3 for a significant percentage of time as GABA is entering the electrostatic field (indicated by the highlighted red region), whereas in the BIND and PARTIAL simulations Arg207 does not occupy this rotameric conformation at all during the time GABA is entering the electrostatic field.