title: Formation of non-beta 6.3-helical gramicidin channels between sequence-substituted gramicidin analogues.
abstract: Using the linear gramicidins as an example, we have previously shown how the statistical properties of heterodimeric (hybrid) channels (formed between the parent [Val1]gramicidin A (gA) and a sequence-altered analogue) can be used to assess whether the analogue forms channels that are structurally equivalent to the parent channels (Durkin, J. T., R. E. Koeppe II, and O. S. Andersen. 1990. J. Mol. Biol. 211:221-234). Generally, the gramicidins are tolerant of amino acid sequence alterations. We report here an exception. The optically reversed analogue, gramicidin M- (gM-) (Heitz, F., G. Spach, and Y. Trudelle. 1982. Biophys. J. 40:87-89), forms channels that are the mirror-image of [Val1]gA channels; gM- should thus form no hybrid channels with analogues having the same helix sense as [Val1]gA. Surprisingly, however, gM- forms hybrid channels with the shortened analogues des-Val1-[Ala2]gA and des-Val1-gC, but these channels differ fundamentally from the parent channels: (a) the appearance rate of these heterodimers is only approximately 1/10 of that predicted from the random assortment of monomers into conducting dimers, indicating the existence of an energy barrier to their formation (e.g., monomer refolding into a new channel-forming conformation); and (b), once formed, the hybrid channels are stabilized approximately 1,000-fold relative to the parent channels. The increased stability suggests a structure that is joined by many hydrogen bonds, such as one of the double-stranded helical dimers shown to be adopted by gramicidins in organic solvents (Veatch, W. R., E. T. Fossel, and E. R. Blout. 1974. Biochemistry. 13:5249-5256).
authors.affiliation: Department of Physiology and Biophysics, Cornell University Medical College, New York, New York 10021.
authors.forename: J T
authors.initials: JT
authors.lastname: Durkin
authors.forename: L L
authors.initials: LL
authors.lastname: Providence
authors.forename: R E
authors.initials: RE
authors.lastname: Koeppe
authors.forename: O S
authors.initials: OS
authors.lastname: Andersen
mesh_terms: D000595:Amino Acid Sequence; D055592:Biophysical Phenomena; D001703:Biophysics; D004563:Electrochemistry; D006096:Gramicidin / Q000737:chemistry*; D007473:Ion Channels / Q000737:chemistry*; D007477:Ions; D008565:Membrane Proteins / Q000737:chemistry; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010539:Permeability; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D007473:Ion Channels; D007477:Ions; D008565:Membrane Proteins; D011994:Recombinant Proteins; D006096:Gramicidin