The association of two gramicidin A (gA) peptides via H-bonds in lipid bilayers causes the formation of an ion channel that is selective for monovalent cations only. In this study, two gAs were covalently linked with a dioxolane group (SS dimer). Some functional properties of natural gA channels were compared to that synthetic dimer in Na+- or Cs+-containing solutions. The SS dimer remained in the open configuration most of the time, while natural gA channels had a relatively brief mean open time. Single channel conductances to Na+ (g Na ) or Cs+ (g Cs ) in the SS dimer were smaller than in natural gA. However, g Na was considerably more attenuated than g Cs . This probably results from a tight solvation of Na+ by the dioxolane linker in the SS channel. In Cs+ solutions, the SS had frequent closures. By contrast, in Na+ solutions the synthetic dimer remained essentially in the open state. The mean open times of SS channels in different solutions (T open,Na > T open,Cs > T open,H ) were inversely proportional to the single channel conductances (g H > g Cs > g Na ). This suggests that ion occupancy inside the pore stabilizes the open configuration of the gA dimer. The mean closed time of the SS dimer was longer in Cs+ than in H+ solutions. Possible mechanisms for these effects are discussed.
The Journal of Membrane Biology – Springer Journals
Published: Apr 1, 2000
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