Detailed Structure and Dynamics of Bicelle Phospholipids Using Selectively Deuterated and Perdeuterated Labels. ²H NMR and Molecular Mechanics Study

Abstract

Dimyristoylphophatidylcholine (DMPC) has been entirely or selectively deuterated on the headgroup, glycerol backbone, and acyl chains. Solid-state deuterium and phosphorus NMR was applied to this lipid with the aim to comprehensively depict its structure and dynamics when embedded in bicelles or in liposomes. Molecular mechanics calculations were also accomplished on fully hydrated DMPC bilayers. The main results are fourfold. (a) The local lipid dynamics across the entire membrane thickness could be accurately described: the glycerol backbone shows a very restricted motional freedom and can be considered as a semirigid “rotula” separating two very fluid zones, the phosphocholine headgroup facing the water medium and the acyl chains constituting the oily bilayer interior. (b) The location of the principal axis of motion of the glycerol backbone of DMPC and its molecular order parameter, S mol, were calculated by making use of NMR, molecular mechanics, and X-ray data reported in earlier studies. Although the later lacks in accurate structural data for hydrogen atoms, there is nonetheless a general trend for an orientation of the glycerol g2−g3 carbon−carbon bond at about 28° with respect to the bilayer normal and for a S mol value of 0.55 for 78% DMPC embedded in bicelles. (c) The two DMPC conformers A and B that were earlier reported in the crystal (Pearson, H.; Parsher, I. Nature 1979, 181, 499−501) also exist in all molecular dynamics runs of fully hydrated DMPC. (d) There is a marked decrease of the DMPC phase transition temperature upon increasing selective deuterium content in the lipid structure. Interestingly, labeling of the five glycerol backbone positions induces the same temperature decrease as a full chain deuteration (54 positions).

Membrane-Perturbing Properties of Two Arg-Rich Paddle Domains from Voltage-Gated Sensors in the KvAP and HsapBK K+ Channels

“…• C for DMPC-d 54 , 41 assuring that the bicelles are in the lamellar liquid crystalline state, L α . Standard quadrupolar delay spectra (π/2-τ 1 -π/2-τ 2 -acq) were acquired for both bicelle solutions with and without peptides, using a π/2 pulse width of 14 µs, and with the delays set to τ 1 =50 µs and τ 2 =48 µs.…”

Bicelles as model membranes for solid‐ and solution‐state NMR studies of membrane peptides and proteins

“…As described extensively (31,72,85 ), this order parameter is the product of several contributions, including bicelle wobbling, intramolecular motions such as trans-gauche isomerizations, and anisotropic reorientation of the whole phospholipid molecules. Hence it is possible to determine variations in lipid chain order by monitoring changes in ⌬ Q values.…”

“…This atomic substitution does not affect the lipid organization (90), and the weak natural abundance of deuterium (0.016%) does not contribute to the spectra. However, the gel-to-fluid phase transition of DMPC is slightly decreased (ϳ2°C) by the deuteration of the molecule (85).…”

“…Bicelle wobbling has been shown to be important at small q values (q Ͻ ϳ3.0), therefore it is preferable to investigate dynamical effects in 2 H NMR spectra of bicelles at higher q values (29,72,85). 2 H NMR has been used extensively to investigate the binding and penetration depth of diverse peptides to bicelles and/or anionic bicelles such as the myristoylated N-terminal 14-residue peptides of cat-14 (catalytic subunit of protein kinase A) (25 ) and pp60 -src (27), a series of antibiotic peptides extracted from frog skin (67), and the 35-residue fragment of a tyrosine kinase receptor Neu TM35 (93).…”

Impact of Strong and Weak Lipid-Protein Interactions on the Structure of a Lipid Bilayer on a Gold Electrode Surface

“…However, increased tilt of the orientation of the C=O bond in the bilayer containing recoverin agrees very well with a higher average tilt angle of the hydrocarbon chains as compared to the protein-free bilayer. According to the X-ray data, [64,74] the C=O bond in the most common DMPC molecule makes a normal angle to the direction of the hydrocarbon chains. Due to the presence of the hydrocarbon chains in the liquid state and low intensities of the C=O stretching mode our calculations have a significant error.…”