Figure 7. Calculation of the channel diameters of HlyA and HlyA_Δ71–110 from the single-channel conductance.

The single-channel conductance data of HlyA and HlyA_Δ71–110 were fitted by using the Renkin correction factor multiplied by the aqueous diffusion coefficients of the different cations. The single-channel conductance for the different cations taken from Table 2 was normalized to that observed for Rb⁺ (hydrated ion radius  = 0.105 nm), which was set to 1.0, and plotted versus the hydrated ion radii taken from Table 3 of Maier et al. [60]. The points correspond to the single-channel conductance observed with Li⁺, Na⁺, K⁺, Cs⁺, N(CH₃)₄ ⁺, N(C₂H₅)₄ ⁺, and Tris⁺, which were all used for the pore diameter estimation (see Discussion). (A) The fit (solid lines) is shown for wildtype HlyA channels with r = 1.6 nm (upper line) and r = 1.0 nm (lower line). The best fit was achieved with r = 1.3 nm (diameter = 2.6 nm), which corresponds to the broken line. (B) The fit (solid lines) is shown for the HlyA_Δ71–110 channels with r = 1.1 nm (upper line) and r = 0.7 nm (lower line). The best fit of all data was achieved with r = 0.9 nm (diameter = 1.8 nm), which corresponds to the broken line.