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Conductive Properties and Gating of Channels Formed by Syringopeptin 25A, a Bioactive Lipodepsipeptide from Pseudomonas syringae pv. syringae, in Planar Lipid Membranes

May 1999 , Volume 12 , Number  5
Pages  401 - 409

Mauro Dalla Serra , 1 Ivonne Bernhart , 1 Paola Nordera , 1 Domenico Di Giorgio , 2 Alessandro Ballio , 2 and Gianfranco Menestrina 1

1CNR-ITC Centro Fisica Stati Aggregati, Via Sommarive 18, I-38050 Povo (Trento), Italy; 2Dipartimento di Scienze Biochimiche e Centro CNR di Biologia Molecolare, Roma “La Sapienza,” P.le Aldo Moro 5, 00185 Roma, Italy

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Accepted 22 January 1999.

Syringopeptin 25A, a pseudomonad lipodepsipeptide, can form ion channels in planar lipid membranes. Pore conductance is around 40 pS in 0.1 M NaCl. Channel opening is strongly voltage dependent and requires a negative potential on the same side of the membrane where the toxin was added. These pores open 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 also present. The voltage dependence of the rates of opening and closing of the stable pores is exponential. This allows estimation of the equivalent charge that is moved across the membrane during the process of opening at about 2.6 elementary charges. When NaCl is present, the pore is roughly 3 times more permeant for anions than for cations. The current voltage characteristic 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 the 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.

Additional keyword: selectivity.

© 1999 The American Phytopathological Society