Solvent determined conformation of gramicidin affects the ability of the peptide to induce hexagonal HH phase formation in dioleoylphosphatidylcholine model membranes

Abstract

It is shown by 3t P-NMR and small angle X-ray scattering that induction of an hexagonal H n phase in dioleoylphosphatidylcholine model membranes by external addition of gramicidin A' depends on the solvent which is used to solubilize the peptide. Addition of gramicidin from dimethylsulfoxide or trifluoroethanol solution leads to H n phase formation whereas addition of the peptide from ethanol does not. This solvent dependence is shown by circular dichroism to be correlated with the peptide conformation. The channel conformation appears to be responsible for H n phase formation by gramicidin.Gramicidin A is an effective promoter of hexagonal HII phases in model and biological membranes [1]. This effect is a consequence of the specific chemical structure of this pentadecapeptide, in particular with respect to the presence of the four tryptophans at the C-terminal part of the molecule [1][2][3]. It was proposed that these bulky residues would provide a pronounced cone shape to the molecule which, within the shape-structure concept of polymorphism [4], together with the peptide's tendency to self associate into cylindrical structures [5][6][7] would explain the Hll phase-inAbbreviations: CD, circular dichroism; DMSO, dimethylsulfoxide; DOPC, dioleoylphosphatidylcholine.

Large unselective pore in lipid bilayer membrane formed by positively charged peptides containing a sequence of gramicidin A

“…The spectrum of P1C in DOPC did not change significantly after heat incubation and was similar to that of gA. The CD spectra of gA in DPhPC and in DOPC were fairly similar and agreed with those for gA in DOPC published earlier [20]. These spectra correspond to the typical singlestranded b 6.3 -helical conformation of the peptide [21].…”

Relationship between gramacidin conformation dependent induction of phospholipid transbilayer movement and hexagonal HII phase formation in erythrocyte membranes

“…1I).). This is in agreement with the observation that gramicidin upon addition from ethanol does not induce H n phase in DOPC [10] model membranes. Addition of larger quantifies of gramicidin, even up to a 1 : 2 molar ratio with respect to the phospholipid content, did not lead to H u phase induction.…”

“…On the other hand ~mparab!e structures could not be det.ected with either technique in samples of g.hosts to which gramicidin was added from ethanol. In analogy with model membrane experiments [10] it can be suggested that the conformation of gramicidin i rserted in the erythrocyte membrane from ethan,~, ~ is unable to induce the H n phase formation attd that for H n phase formation the/]6.3 conformation is essential.…”

“…Recently it was demonstrated that the solvent history of gramicidin determines the conformation of the polypeptide upon incorporation in model membranes [10,11] and is crucial for its ability to induce H, phase formation in dioleoylphosphatidy1'~hr,i;n ~ (DOPC) r,a~cI ---~" ..... [!0]. I.~ g~ been suggested that for the induction of the H a phase the fl6.3 conformation, which prevails upon insertion from dimethylsulfoxide or trifluoroethanol, is a prerequisite [11].…”

Vibrational circular dichroism of gramicidin D in organic solvents

“…The structure of gramicidin in trifluoroethanol (TFE), was suggested to be similar to that in DMSO solutions. 16,17 In both solvents, thin layer chromatography indicated only one spot indicating the presence of a single monomeric species in these solutions. 8 The structure of gramicidin in solution is found to change in the presence of cations.…”