Colicin N forms voltage- and pH-dependent channels in planar lipid bilayer membranes

Abstract

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.

In vitro Approaches to Investigation of the Early Steps of Colicin‐Ompf Interaction

“…Moreover, the investigations carried out with an unfolded colicin, obtained after SDSPAGE and electrotransfer to nitrocellulose, indicate that the OmpF-binding site is conserved under these conditions. It is interesting to compare these results with the increase of colicin A activity reported after denaturation of the colicin with urea [25] and with the similar protease susceptibility of the NH,-terminal parts of colicins A and N [9,26,27]. Considering these findings, we speculate that a stretch of amino acid residues located in the receptorrecognition domain of colicin [14] participates in the porinbinding site, its exposure being modulate by the interdomain interactions.…”

The bacteriocin lactococcin A specifically increases permeability of lactococcal cytoplasmic membranes in a voltage-independent, protein-mediated manner

“…3A). Several bacteriocins have been described to have a voltage-dependent pore-forming ability (1,8,16,17,23,27,28,35). To investigate whether this also applied to lactococcin A, cells of strain IL1403 were allowed to accumulate glutamate and were then treated with valinomycin and nigericin to collapse the proton motive force, and lactococcin A was subsequently added.…”

A Natively Unfolded Toxin Domain Uses Its Receptor as a Folding Template

“…Pore formation by colicin N and its relatives has been extensively studied (6,30,31), but less is known about the receptor binding or translocation steps. Since requirements for receptor binding and translocation of colicin N are relatively simple, it is a good model for studying mechanisms of colicin translocation, and this has permitted a particularly detailed analysis of the T-domain (32)(33)(34).…”