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The outer membrane proteins TolC and EefC from Enterobacter aerogenes are involved in multidrug resistance as part of two resistance-nodulation-division efflux systems. To gain more understanding in the molecular mechanism underlying drug efflux, we have undertaken an electrophysiological characterization of the channel properties of these two proteins. TolC and EefC were purified in their native trimeric form and then reconstituted in proteoliposomes for patch-clamp experiments and in planar lipid bilayers. Both proteins generated a small single channel conductance of about 80 pS in 0.5 M KCl, indicating a common gated structure. The resultant pores were stable, and no voltage-dependent openings or closures were observed. EefC has a low ionic selectivity (P(K)/P(Cl)= approximately 3), whereas TolC is more selective to cations (P(K)/P(Cl)= approximately 30). This may provide a possible explanation for the difference in drug selectivity between the AcrAB-TolC and EefABC efflux systems observed in vivo. The pore-forming activity of both TolC and EefC was severely inhibited by divalent cations entering from the extracellular side. Another characteristic of the TolC and EefC channels was the systematic closure induced by acidic pH. These results are discussed in respect to the physiological functions and structural models of TolC and EefC.

The ability of three primary amphipathic Cell-Penetrating Peptides (CPPs) CH3-CO-GALFLGFLGAAGSTMGAWSQPKKKRKV-NH-CH2-CH2-SH, CH3-CO-GALFLAFLAAALS LMGLWSQPKKKRKV-NH-CH2-CH2-SH, and CH3-CO-KETWWETWWTEWSQPKKKRKV-NH-CH2-CH2-SH called Pbeta, Palpha and Pep-1, respectively, to promote pore formation is examined both in Xenopus oocytes and artificial planar lipid bilayers. A good correlation between pore formation and their structural properties, especially their conformational versatility, was established. This work shows that the cell-penetrating peptides Pbeta and Pep-1 are able to induce formation of transmembrane pores in artificial bilayers and that these pores are most likely at the basis of their ability to facilitate intracellular delivery of therapeutics. In addition, their behaviour provides some information concerning the positioning of the peptides with respect to the membrane and confirms the role of the membrane potential in the translocation process.