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Microcin E492 forms ion channels in phospholipid bilayer membrane
R Lagos1, M Wilkens, C Vergara
1Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago.
Abstract:
Microcin E492, a polypeptide antibiotic, has been shown to have an M(r) of 6,000 by urea-SDS-polyacrylamide gel electrophoresis of the fluorescently labelled compound. It is known that the bactericidal action of microcin involves a loss of the transmembrane potential. In this study we show that microcin forms cation-selective channels in planar phospholipid bilayers. The channels have two main conductance states the current-voltage curves of which rectify. The reversal potentials measured under biionic conditions indicate a permeability sequence of NH4+ > K+ = Rb+ = Cs+ > Na+ = Na+ = Li+ > Tris+. The results suggest that membrane potential dissipation induced by microcin is a consequence of the formation of pores in the bacterial membrane.
Insights
Microcin E492, a polypeptide antibiotic, forms cation-selective channels in bacterial membranes. This pore formation leads to membrane potential dissipation and bactericidal action, explaining its antibiotic mechanism.
Area of Science:
- Molecular Biology
- Biophysics
- Antimicrobial Research
Background:
- Microcin E492 is a polypeptide antibiotic known to disrupt bacterial membrane potential.
- The precise mechanism of microcin's bactericidal action, particularly its interaction with cell membranes, requires further elucidation.
Purpose of the Study:
- To investigate the molecular mechanism by which Microcin E492 exerts its bactericidal effect.
- To determine if Microcin E492 forms channels in lipid bilayers and characterize their properties.
Main Methods:
- Fluorescent labeling of Microcin E492 followed by urea-SDS-polyacrylamide gel electrophoresis to determine its molecular mass.
- Planar phospholipid bilayer experiments to form and record ion channel activity induced by Microcin E492.
- Current-voltage (I-V) curve analysis and bi-ionic potential measurements to characterize channel selectivity and conductance states.
Main Results:
- Microcin E492 forms cation-selective channels in planar phospholipid bilayers.
- These channels exhibit two main conductance states with rectifying current-voltage characteristics.
- Permeability sequence determined as NH4+ > K+ = Rb+ = Cs+ > Na+ = Li+ > Tris+.
Conclusions:
- Microcin E492 functions by forming pores in the bacterial membrane.
- The formation of these cation-selective channels leads to membrane potential dissipation, explaining the antibiotic's bactericidal activity.