Fig. 5.
VopQ forms a gated channel in membranes. (A) Current recorded after 25 nM MBP-VopQ was incubated with a POPC/DOPS (85:15 molar ratio) bilayer. (Upper) The voltage pulse stimulation is shown. (B) The averaged ramp current after the capacitance components were subtracted. The red trace was a linear fit from 0 mV to +30 mV with a chord conductance of 448.11 ± 1.67 pS. The inactivation of the channel becomes obvious when the voltage is higher than 40 mV or lower than −20 mV. (C) VopQ single-channel activity at different transmembrane voltages. C, close state; O, open state. (D) Histogram of single-channel events at +80 mV. We estimated the pore diameters by applying the Nernst–Planck equation, 
, for specific ion k. The measured current in our recordings was expressed as the sum of sodium and chloride flows, and the estimated pore diameter is ∼18 Å. (E) The measured single-channel current–voltage relation. The linear fitting (red line) yields a single-channel conductance of 128.9 ± 3.4 pS. (F) VopQ (25 nM) incubated with 100% POPC membranes did not produce any channel activity (80 mV, n = 4). MBP (25 nM) incubated with POPC/DOPS membranes did not produce any channel activity (80 mV, n = 6).