The effect of POPC acyl chains packing by aromatic amino acid methyl esters investigated by ATR-FTIR combined with QM calculations

Abstract

Aromatic residues play important roles in modulating the function of proteins and binding of proteins to biomembranes. However, the effect of small molecules which contain aromatic residues on the packing of unsaturated lipid acyl chains and the dynamics properties in membrane bilayers remains unclear. The membrane interactions of a series of amino acid methyl esters have been investigated to establish how different amino acids influence lipid acyl chains packing. Attenuated total reflectance-Fourier transform infrared spectroscopic (ATR-FTIR) measurements show that the ]CH and C]C stretching vibrational bands of 2-oleoyl-1-pamlitoyl-sn-glyecro-3-phosphocholine (POPC) present evident red-shifts when aromatic amino acid methyl esters are mixed into membrane bilayers. Quantum mechanical (QM) calculations further demonstrate that the red shifts of the ]CH and C]C stretching modes for POPC acyl chains are not through a direct interaction between the side chain groups and the HC]CH motif but are mainly caused by the conformational change of POPC acyl chains, in which the HC]CH motif is packed closed to the other one of an adjacent acyl chain with enhancement by dispersion interactions. The implication of these findings is that the packing of POPC acyl chains can be significantly influenced by aromatic amino acid methyl esters. This work may provide valuable insight into the effect on the lipid acyl chains packing by small molecules interacting with membranes and offer possibilities for the dynamic control of membrane fusion and binding of proteins to the membrane.

Membrane Permeability and Its Activation Energies in Dependence on Analyte, Lipid, and Phase Type Obtained by the Fluorescent Artificial Receptor Membrane Assay

“…The low activation energy for Trp-OMe appears to be responsible for the very fast permeation rate of this analyte, the fastest in this series. − In fact, its fluorescence decay kinetics were needed to be followed by stopped-flow measurements (Figures S9 and S10). However, even with this technique, a limiting value for the kinetics was reached at high temperatures.…”

“…Although these data were omitted for the fitting of the temperature dependence (Figure ), the different behavior and measurement methods could be responsible for the low activation energy of Trp-OMe. An alternative explanation, proposed in a different context, is that the addition of aromatic amino acid methyl esters can cause changes in the molecular packing or fluidity of the POPC bilayer itself.…”

Understanding the Structural Pathways for Lipid Nanodisc Formation: How Styrene Maleic Acid Copolymers Induce Membrane Fracture and Disc Formation

“…33 The stronger interactions between POPC and SMA(3:1) may be due to favorable interactions between the acyl chain double bonds and the SMA(3:1) aromatic styrene residues. 36 Such interactions, along with the lower tolerance of gel-phase DMPC and higher tolerance of POPC to solubilization, show that both temperature and the lipid composition of the bilayers should be taken into account when preparing SMA nanodiscs. Another parameter that would be important to consider is the styrene/maleic acid ratio of the polymer itself.…”

The chain order of binary unsaturated lipid bilayers modulated by aromatic-residue-containing peptides: an ATR-FTIR spectroscopy study

“…the structural changes in membranes induced via interactions with small molecules, 25,26 or antimicrobial cationic lipopeptides, 27 etc. Changes in the width and position of the lipid IR peaks can provide useful information regarding lipid membrane dynamics 28 and interactions of lipids with proteins.…”