Figure 1.

Electrophysiological analysis of KR2_βHK in X. laevis oocytes. (A) A sketch about the intention of this scientific work is shown. (B) Quantitative comparison of the stationary photocurrent amplitudes (see Fig. S6A for details). (C) Representative photocurrent traces of wild-type (WT) KR2 at pH_o = 7.5 and different holding potentials (in 25 mV steps) are shown. (D) The KR2 crystal structure (PDB: 3X3C) at neutral pH is shown, illustrating the mutated positions of the counterion complex. (E) Substitution of the proposed primary proton acceptor (D116N) causes pH_o-dependent transient photocurrents. Traces at −125 mV (blue) and +75 mV (red) for each pH_o value are displayed. (F–J) Photocurrents of additional mutants are shown at pH_o = 10. All traces were measured in extracellular buffer containing 100 mM NaCl. Oocytes were illuminated with 500 ms light pulses, using a xenon lamp and a 400–600 nm broadband filter. To see this figure in color, go online.