Conductive properties and gating of channels formed by syringopeptin 25A, a bioactive lipodepsipeptide from Pseudomonas syringae pv. syringae, in planar lipid membranes

Syringopeptin 25A, a pseudomonad lipodepsipeptide, can form ion channels in planar lipid membranes. Pore conductance is around 40 pS in 0.1M NaCl. Cha nnel opening is strongly voltage dependent and requires a negative potentia l on the same side of the membrane where the toxin was added. These pores o pen and close with a lifetime of several seconds. At negative voltages, an additional pore state of around 10 pS and a lifetime of around 30 ms is als o present. The voltage dependence of the rates of opening and closing of th e stable pores is exponential. This allows estimation of the equivalent cha rge that is moved across the membrane during the process of opening at abou t 2.6 elementary charges. When NaCl is present, the pore is roughly 3 times more permeant for anions than for cations, The current voltage characteris tic of the pore is nonlinear, i.e., pore conductance is larger at negative than at positive voltages. The maximal conductance of the pore depends on t he concentration of the salt present, in a way that varies almost linearly with the conductivity of the solution. From this, an estimate of a minimal pore radius of 0.4 nm was derived.