Colicin N forms voltage- and pH-dependent channels in planar lipid bilayer membranes.
The protein antibiotic colicin N forms ion-permeable channels through planar lipid bilayers. Channels are induced when positive voltages higher than +60 mV are applied. Incorporated channels activate and inactivate in a voltage-dependent fashion. It is shown that colicin N undergoes a transition between an "acidic" and a "basic" channel form which are distinguishable by different voltage dependences. The single-channel conductance is non-ohmic and strongly dependent on pH, indicating that titratable groups control the passage of ions through the channel. The ion selectivity of colicin N channels is influenced by the pH and the lipid composition of the bilayer membrane. In neutral membranes the channel undergoes a transition from slightly cation-selective to slightly anion-selective when the pH is changed from 7 to 5. In lipid membranes bearing a negative surface charge the channel shows a more pronounced cation selectivity which decreases but does not reverse upon lowering the pH from 7 to 5. The high degree of similarity between the channel characteristics of colicin A and N suggests that the channels share common features in their molecular structure.
Europäisches Laboratorium für Molekularbiologie, Heidelberg, Federal Republic of Germany.
H U
HU
Wilmsen
A P
AP
Pugsley
F
F
Pattus
D003087:Colicins / Q000378:metabolism*; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating; D007473:Ion Channels / Q000378:metabolism*; D007700:Kinetics; D008051:Lipid Bilayers
D003087:Colicins; D007473:Ion Channels; D008051:Lipid Bilayers