Fluorescent gramicidin derivatives for single-molecule fluorescence and ion channel measurements

Single-molecule spectroscopies in combination with single-channel patch-cla mp measurements have the potential for providing new information on ion cha nnel gating processes. Fluorescent gramicidin derivatives could provide a m eans for calibrating such experiments since the structure of the open chann el is known and the mechanism of gating (peptide dimerization) is generally agreed. We describe here the synthesis and characterization of two pairs o f gramicidin derivatives that should prove useful for such studies. They co ntain robust fluorophores, undergo resonance energy transfer (FRET) when th ey dimerize, and have single-channel properties close to those of the wild- type channel.