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Complex inhibition of OmpF and OmpC bacterial porins by polyamines
1Department of Biology, University of Houston, Houston, Texas 77204-5513, USA.
Abstract:
The effects of four polyamines (putrescine, cadaverine, spermidine, and spermine) on the activity of bacterial porins OmpC and OmpF were investigated by electrophysiology. Membrane vesicles made from the outer membrane of Escherichia coli strains expressing only OmpC or OmpF were reconstituted into liposomes probed by patch clamp. The channel activity was recorded in control solutions and in the presence of increasing concentrations of a specific polyamine. In all cases, concentration- and voltage-dependent inhibitory effects were observed. They include both the suppression of channel openings and the enhancement of channel closures as well as the promotion of blocked or inactivated states. OmpF and OmpC, although highly homologous, have distinct sensitivities to modulation, especially by spermine. This compound inhibits OmpF in the nanomolar range, which is in agreement with its potency on eukaryotic channels. Putrescine was the least effective (upper millimolar range) and also had inhibitory effects qualitatively distinct from those exerted by the other polyamines. The compounds appear to bind to at least two distinct binding sites, one of which resides within the pore. The potencies to this site are lower when the polyamines are applied from the extracellular side than from the periplasmic side, suggesting an asymmetric binding site.
Insights
Polyamines like spermine inhibit bacterial porins OmpC and OmpF by altering channel activity. These findings reveal distinct sensitivities and binding sites, impacting bacterial outer membrane function.
Area of Science:
- Biochemistry
- Molecular Biology
- Biophysics
Background:
- Bacterial porins, such as OmpC and OmpF in Escherichia coli, are crucial outer membrane proteins forming channels for solute transport.
- Polyamines are essential cations involved in various cellular processes, and their interaction with membrane proteins is of significant interest.
Purpose of the Study:
- To investigate the effects of four polyamines (putrescine, cadaverine, spermidine, and spermine) on the activity of bacterial porins OmpC and OmpF.
- To determine the concentration- and voltage-dependent modulation of porin channel function by polyamines.
Main Methods:
- Electrophysiology using patch clamp technique on liposomes reconstituted with outer membrane vesicles from E. coli strains expressing OmpC or OmpF.
- Recording channel activity in the presence of increasing concentrations of specific polyamines.
Main Results:
- All tested polyamines exhibited concentration- and voltage-dependent inhibitory effects on both OmpC and OmpF channel activity.
- Distinct sensitivities to polyamine modulation were observed between OmpC and OmpF, particularly with spermine, which inhibited OmpF at nanomolar concentrations.
- Putrescine showed the least effectiveness and qualitatively distinct inhibitory effects, suggesting varied polyamine-porin interactions.
Conclusions:
- Polyamines modulate bacterial porin activity through binding to at least two sites, one within the pore, with asymmetric affinity.
- The differential sensitivity of OmpC and OmpF to polyamines, especially spermine, highlights specific interactions influencing outer membrane permeability.