Organization of Model Helical Peptides in Lipid Bilayers: Insight into the Behavior of Single-Span Protein Transmembrane Domains

Abstract

Selectively deuterated transmembrane peptides comprising alternating leucine-alanine subunits were examined in fluid bilayer membranes by solid-state nuclear magnetic resonance (NMR) spectroscopy in an effort to gain insight into the behavior of membrane proteins. Two groups of peptides were studied: 21-mers having a 17-amino-acid hydrophobic domain calculated to be close in length to the hydrophobic thickness of 1-palmitoyl-2-oleoyl phosphatidylcholine and 26-mers having a 22-amino-acid hydrophobic domain calculated to exceed the membrane hydrophobic thickness. (2)H NMR spectral features similar to ones observed for transmembrane peptides from single-span receptors of higher animal cells were identified which apparently correspond to effectively monomeric peptide. Spectral observations suggested significant distortion of the transmembrane alpha-helix, and/or potential for restriction of rotation about the tilted helix long axis for even simple peptides. Quadrupole splittings arising from the 26-mer were consistent with greater peptide "tilt" than were those of the analogous 21-mer. Quadrupole splittings associated with monomeric peptide were relatively insensitive to concentration and temperature over the range studied, indicating stable average conformations, and a well-ordered rotation axis. At high peptide concentration (6 mol% relative to phospholipid) it appeared that the peptide predicted to be longer than the membrane thickness had a particular tendency toward reversible peptide-peptide interactions occurring on a timescale comparable with or faster than approximately 10(-5) s. This interaction may be direct or lipid-mediated and was manifest as line broadening. Peptide rotational diffusion rates within the membrane, calculated from quadrupolar relaxation times, T(2e), were consistent with such interactions. In the case of the peptide predicted to be equal to the membrane thickness, at low peptide concentration spectral lineshape indicated the additional presence of a population of peptide having rotational motion that was restricted on a timescale of 10(-5) s.

Characterisation of intestinal peptide transporter of the Antarctic haemoglobinless teleostChionodraco hamatus

“…5). In this case, as expected, the temperature range of physiological activity of the transporter is narrower, in agreement with the complex temperature requirements of a trans-membrane carrier protein and the specificity of proteo-lipid interactions (Maffia and Acierno, in press;Sharpe et al, 2002). The structure of a protein that spans the entire cell membrane is markedly affected by the physicochemical state of the lipid bilayer, which provides the required degree of plasticity to permit the conformational protein changes necessary for substrate translocation.…”

Prediction, refinement, and persistency of transmembrane helix dimers in lipid bilayers using implicit and explicit solvent/lipid representations: Microsecond molecular dynamics simulations of ErbB1/B2 and EphA1

“…Helix dissociation/association has recently been measured to occur on a timescale of 50 ms for the weakly bound ErbB4 system 46. However, the timescale of helix motions in membranes, such as translational and rotational diffusion of individual helixes or helices within dimers has been reported on the order of 1 to 100 μs 47, 48. This is slower than could be sampled here, although at least one large transition is seen for the orientation of one of the helices in each system (Fig.…”

Mesoscopic models of biological membranes

“…The occurrence of lateral inhomogeneities in the membrane may, among others, cause membrane fusion, as suggested by Nielsen et al [208], and it may affect passive permeability to small ions or solutes. There may be mismatch effects which are lipid-mediated, such as the tilting (or even bending) of a whole protein/peptide to adapt to a too thin bilayer [181,[209][210][211][212][213][214][215][216], or even tilting of the individual helices which form a protein. There is indeed some indirect experimental evidence that this is the case for channel proteins [180] and even proteins like Rhodopsin [217], suggesting that a change of the tilt-angle of the individual helices could cause changes in protein activity.…”