Figure 5.

Test of the hypothesis that the partial charges at the poles of helix 2b act as voltage sensors. (A) Adding a negatively charged residue to the positive pole of the helix by site directed mutagenesis (L80D) accelerate voltage induced channel closings. (B) A single exponential fit (blue line) to the lifetime histogram indicates a channel lifetime of about 0.2 s at φ = −140 mV. (C) In contrast, closings at φ = −140 mV of SecYEG-RNC complex are slower with the addition of a positive residue to the tip of helix 2b (L80K). (D) The single exponential fit to the lifetime histogram shows a lifetime of about 2.5 s. The color code of the small schemes is the same as in Figure 1.