The solution conformations of gramicidin A and its analogs

The double ??5.6 helix of gramicidin a predominates in unsaturated lipid membranes

“…Recent studies by 2D-NMR and X-ray confirmed the coordinates obtained theoretically for T Snn5.6 and TlnnT.2 (Arseniev et al 1984(Arseniev et al , 1985bLangs 1988), whereas major differences were observed between theoretically deduced and experimentally obtained q~L, 7JL, ~0~, 7' D values for ]'~nn and n6----~, n6.~-3 (Arseniev et al 1985 a;Barsukov IL et al 1987b). Apparently, this is the main reason why computed frequences and resonance splittings of the amide I band for T T tin 5.6 and ~ n~6.3 helices predicted in Sychev et al (1980) and Naik and Krimm (1986) are inaccurate, whereas spectra calculated for T $ n n helices correlate well with the experimental data (see below and Fig. 12).…”

“…Therefore it is most likely that the changes reflect major conformational transitions in the peptide backbone, rather than in side chains only. Negative CD curves of GA in the 200-250 nm range have been assigned to left-handed, and positive curves -to the righthanded helices (Sychev et al 1980). This assignment has been confirmed by the 2D-NMR technique (Arseniev et al 1984(Arseniev et al , 1985a.…”

“…Correlation between the dynamic parameter D± and the fraction of double helices in lipids (Table 2) indirectly supports the membrane fluidity concept discussed above. Lotz et al (1976) From Sychev et al (1980) d From Heitz et al (1986 The present work provides a successful example of the combined application of FTIR and CD techniques for studying the channel -former structures in membranes of variable lipid composition. The first attempt to apply calculation of the amide I band fine structure in studying GA was made by Sychev et al (1980) when GA was ascribed the T $nn5.6 helical structure in dioxane solution.…”

“…For these species proposed conformations of parallel and antiparallel double helices (1" Tnn and T ~nn). It was shown by 2D-NMR in ethanol (Arseniev et al 1984(Arseniev et al , 1985 a) that species 1 and 2 are left-handed T T nrI5.6 helices (5.6 residues/turn) differing in a relative shift of the polypeptide chains, species 3 is the left-handed ~ + nn 5.6 helix (the dominant structure in solution determined also by calculation of IR spectra (Sychev et al 1980)), and species 4 is the right-handed T Tnn5.6 helix.…”

Vibrational circular dichroism of gramicidin D in organic solvents

“…Dioxane, CHCl 3 , CDCl 3 , ethanol, and propanol form one group of solvents where gramicidin has similar absorptions, so the structure of gramicidin might be considered similar (see below) in these solvents. The amide I region absorption spectrum of gramicidin in these solvents is similar to that of isolated species 3 in chloroform, 9 where it was predicted to have left-handed antiparallel double helical structure and also to that of isolated species 3 in dioxane, 26 where the structure was determined from NMR studies also to be 12 5.6(left). 11 The amide I absorption band maximum position is at a significantly higher frequency (1663 cm Ϫ1 ) in DMSO-d 6 , so the structure of gramicidin in DMSO-d 6 must be significantly different from that in other solvents considered above.…”