On the Helix Sense of Gramicidin-a Single Channels
by Koeppe, R. E.; Providence, L. L.; Greathouse, D. V.; Heitz, F.; Trudelle, Y.; Purdie, N.; Andersen, O. S.
In order to resolve whether gramicidin A channels are formed by right- or left-handed beta-helices, we synthesized an optically reversed (or mirror image) analogue of gramicidin A, called gramicidin A-, to test whether it forms channels that have the same handedness as channels formed by gramicidin M- (F. Heitz et al., Biophys. J. 40:87-89,1982). In gramicidin M- the four tryptophan residues have been replaced with phenylalanine, and the circular dichroism (CD) spectrum therefore reflects almost exclusively contributions from the polypeptide backbone. The CD spectrum of gramicidin M- in dimyristoylphosphatidylcholine vesicles is consistent with a left-handed helical backbone folding motif (F. Heitz et al., Biophys. Chem. 24:149-160, 1986), and the CD spectra of gramicidins A and A- are essentially mirror images of each other. Based on hybrid channel experiments, gramicidin A- and M-channels are structurally equivalent, while gramicidin A and A- channels are nonequivalent, being of opposite helix sense. Gramicidin A- channels are therefore left-handed, and natural gramicidin A channels in phospholipid bilayers are right-handed beta-6.3-helical dimers.
- Journal
- Proteins-Structure, Function, and Bioinformatics
- Volume
- 12
- Issue
- 1
- Year
- 1992
- Start Page
- 49-62
- URL
- https://dx.doi.org/10.1002/prot.340120107
- ISBN/ISSN
- 1097-0134; 0887-3585
- DOI
- 10.1002/prot.340120107