Fig. 2: Influence of GABA on Best2 structure and function.

a Side view of GABA-bound Best2 with GABA molecule shown as blue sticks. PM, plasma membrane. Black box indicates region of focus in panel (b). b Close-up of the GABA binding site with hydrogen bonds depicted as dotted lines and interacting residue side chains labeled. c, d Top views of Best2 (from the extracellular side) with GABA molecules shown as blue spheres, I76 as brown spheres, and F80/F84 as pink spheres in the fully open (FFFFF, c) and closed (CCCCC, d) states. e Population steady-state current density-voltage (I-V) relationships of Best2 in HEK293 cells at 1 μM [Ca²⁺]_i when Cl⁻ is the principal anion, with or without 100 μM external GABA; n = 6–9 for each point; *p < 0.05 compared to no GABA. I, intracellular; E, extracellular. f Normalized steady-state current density at +100 mV (Y axis) plotted against different concentrations of external GABA (X axis) and fitted to the Hill equation; n = 6–9 for each point. g, h I-V relationships of Best2 in HEK293 cells, with Cl⁻ as the principal anion and 100 μM GABA in the external solution (g), or with internal glutamate and external Cl⁻ (h); n = 5–7 for each point, *p < 0.05 compared to 1 μM [Ca²⁺]_i. i I-V relationships of Best2 at 1 μM [Ca²⁺]_i when Cl⁻ is the principal anion (black), compared to that when GABA is the principal ion in the external solution; n = 7–9 for each point. j Relative ion conductance ratios (G_GABA/G_Cl) measured as slope conductance at the reversal potential plus 50 mV (GABA/Cl, gray) or minus 50 mV (Cl/Cl, black) at 1 μM [Ca²⁺]_i; n = 7 for each bar. k I-V relationships of Best2 at 1 μM [Ca²⁺]_i with internal Cl⁻ and external glutamate, in the absence or presence of 100 μM external GABA; n = 5–7 for each point. l G_Glu/G_Cl in the absence or presence of 100 μM GABA; n = 5–7 for each bar. P values are calculated using two-tailed unpaired Student’s t test. All error bars in this figure represent s.e.m.