Figure 1.

Conformational coupling between activation and inactivation gates in K⁺ channels. a. Defining coupling from the selectivity filter to the activation gate by modulating the rate and extent of inactivation. Left panel, KcsA macroscopic currents obtained at 100 mV from liposome-reconstituted KcsA in 100 mM symmetric KCl (red), 100 mM symmetric RbCl (navy blue) or the mutant E71A in 100 mM symmetric KCl (light blue). The right panel shows the extent of inner gate opening for these three conditions in KcsA spin labeled at G116C, and monitored from the amplitude of the central resonance line normalized by the total number of spins. Asolectin-reconstituted spin-labeled channels in 100 mM symmetric KCl (red circles), 100 mM symmetric RbCl (navy blue circles) or the mutant E71A in 100 mM symmetric KCl (light blue circles). b. Defining coupling from the activation gate to the selectivity filter by modulating the extent of inner gate opening. Left, macroscopic currents at 100 mV and 100 mM symmetric KCl for wild-type KcsA (red) or Chymotrypsin C-terminal truncated channel KcsA Δ-125. Right panel, EPR spectra from the spin labeled Y82C mutant in the closed, conductive state (pH 7, black trace); open, inactivated state (pH 3, blue trace); and C-terminal truncated open, inactivated state (pH 3, red trace). EPR spectra were normalized by the total number of spins in the sample.