Figure 5: Mutational analysis to of KR2.
(a) Positions of mutated amino-acid residues (yellow spheres) based on the crystal structure of BR55. We introduced D/N and E/Q mutations into carboxylates at each loop. (b) pH changes caused by light-driven ion pump of E. coli cells suspensions expressing KR2 mutants. The solution contains 100 mM NaCl (blue lines), after addition of CCCP (green lines) and 100 mM KCl (red lines). Light was turned on and off at t=100 s and 400 s, respectively. (c) Quantitatively normalized pump activities of each mutant estimated from the initial slope of light-induced pH changes. Positive and negative signals represent outward sodium pump with subsequent secondary proton uptake and outward proton pump activities, respectively. (d) ATF-FTIR difference spectra of KR2 mutants upon the exchange of 50 mM NaCl/KCl.
