Ionic channels induced by surfactin in planar lipid bilayer membranes.
Surfactin is a lipopeptide produced by certain strains of Bacillus subtilis and has potent surface activity. Here, we present the first results showing that ion-conducting pores can be formed by surfactin in artificial lipid membranes. With a low aqueous concentration of surfactin (1 microM) and a restricted membrane area (5.10(-5) cm2) we observed conductance jumps that indicate the formation of individual ionic channels in the presence of K+, Rb+, Cs+, Na+ or Li+ chlorides. Although for every salt concentration (Ci), the distribution in amplitude of the conductance steps (lambda i) may be rather broad, there is always a step amplitude which is more frequent than the others. In addition, the channels corresponding to this most frequent step amplitude are the longest in duration. For Ci = 1 M, the cationic selectivity sequence deduced from these most frequent events is K+ greater than Rb+ greater than Na+ greater than Cs+ = Li+ with respective values for lambda Mi: 130, 110, 80 and 30 pS. In KCl solutions lambda MKCl increases as a function of Ci for low Ci, and shows a plateau for Ci greater than 0.5 M. When measured on larger area membranes (10(-2)cm2) with 1 M solutions of the monovalent salts KCl, NaCl, RbCl and CsCl or the divalent salt CaCl2, the macroscopic low voltage conductance (G0) increases with a slope of 2 on a log-log plot as a function of surfactin concentration. These results demonstrate that surfactin produces selective cationic channels in lipid bilayer membranes and suggest that at higher salt concentration, a dimer is involved in this functional channel-forming process.
Sheppard
J D
JD
Department of Chemical Engineering, McGill University, Montreal, Canada.
Jumarie
C
C
Cooper
D G
DG
Laprade
R
R
D001412:Bacillus subtilis / Q000032:analysis; D001426:Bacterial Proteins / Q000302:isolation & purification / Q000494:pharmacology*; D004553:Electric Conductivity; D004573:Electrolytes; D007473:Ion Channels / Q000187:drug effects*; D008051:Lipid Bilayers; D055666:Lipopeptides; D008433:Mathematics; D010456:Peptides, Cyclic; D012996:Solutions
D001426:Bacterial Proteins; D004573:Electrolytes; D007473:Ion Channels; D008051:Lipid Bilayers; D055666:Lipopeptides; D010456:Peptides, Cyclic; D012996:Solutions; C009365:surfactin peptide