HELIX-SHEET INTERCONVERSION IN A SYNTHETIC PORE LINING PEPTIDE DERIVED FROM A DESIGNED ION-CHANNEL

We have designed a four-helix protein that is expected to tetramerize in the membrane to form an ion channel with a structurally well define d pore. A synthetic peptide corresponding to the channel lining helix facilitates ion transport across liposomal membranes and largely helic al in membranes. Detailed circular dichroism studies of the peptide in methanol, water and methanal-water mixtures reveal that it is helical in methanol, beta-structured in 97.5% water and a combination of thes e two structures at intermediate compositions of methanol and water. A fluorescence resonance energy transfer study of the peptide shows tha t the peptide is monomeric in methanol but undergoes extensive anti-pa rallel aggregation in aqueous solution.