Conformation of gramicidin A in Triton X‐100 micelles from CD and FTIR data: a clean example of antiparallel double β5.6 helix formation

Abstract

The linear peptide gramicidin A (gA) forms prototypical ion channels specific for monovalent cations and has been extensively used to study the organization and dynamics of membrane channels. This polymorphic peptide can adopt two different types of structures, the helical dimer β6.3 ('channel state') and the double helical structure with two intertwined monomers. The structure of gA in micelles of detergent Triton X-100 has been studied using CD, Fourier transform infrared, and fluorescence spectroscopy. The results obtained demonstrate that only one thermodynamically stable gA structure, the antiparallel left-handed double helix β5.6, is formed in this membrane-mimetic environment. The position of the tryptophan fluorescence maximum at 332 nm is the same as that in phospholipid membranes. The causative factors governing the double helix formation in the micellar medium are discussed on the basis of known physicochemical properties of Triton X-100.

Large scale conformational transitions in β‐structural motif of gramicidin A: kinetic analysis based on CD and FT‐IR data

“…In SDS micelles, gA forms a head‐to‐head β 6.3 helix , whereas in TX‐100, we found a LH ↑↓ β 5.6 double helix . gA was shown to form the RH β 6.3 channel in a saturated lipid membrane, whereas the ↑↓ and ↑↑ β 5.6 helices predominate in unsaturated lipids .…”

“…CD spectrum measured immediately after addition of the complex to the micelles (Figure , curve b) differs notably from that of the complex (curve a) and is symmetric (about horizontal coordinate) to the final curve e, which refer to the LH↑↓ β 5.6 helix, i.e. to the equilibrium structure of gA in TX‐100 micelles as shown in . This symmetry concerns both the B b aromatic transition in Trp residues (228 nm) [] and the peptide n → π٭ and π → π٭ transitions (190–220 nm).…”

“…to the equilibrium structure of gA in TX‐100 micelles as shown in . This symmetry concerns both the B b aromatic transition in Trp residues (228 nm) [] and the peptide n → π٭ and π → π٭ transitions (190–220 nm). It is well known that the RH and LH ↑↑ β 5.6 helices give enantiomeric CD spectra at 200–250 nm .…”

“…On the other hand, only β 6.3 helix forms in SDS micelles in wide range of temperatures . The present kinetic study of sequential long range changes became possible after we have recently shown that ↑↓ β 5.6 helix is the only thermodynamically stable structure of gA in TX‐100 micelles .…”

Effective lipid‐detergent system for study of membrane active peptides in fluid liposomes

“…The spectra were presented in molar ellipticity per residue measured in degrees cm 2 dmol −1 . The measured spectrum can be represented as a linear combination of the distinct CD spectra of RHβ6.3, LH↑↓β5.6, and LH↑↑β5.6 helices (Results): where f are their molar fractions determined by a least‐square fitting algorithm over the 202–250 nm wavelength range as described previously in . The quality of each fit was evaluated by normalized root‐mean‐square deviation, which did not exceed 7%.…”