The dynamical Matryoshka model: 2. Modeling of local lipid dynamics at the sub-nanosecond timescale in phospholipid membranes

Abstract

Biological membranes are generally formed by lipids and proteins. Often, the membrane properties are studied through model membranes formed by phospholipids only. They are molecules composed by a hydrophilic head group and hydrophobic tails, which can present a panoply of various motions, including small localized movements of a few atoms up to the diffusion of the whole lipid or collective motions of many of them. In the past, efforts were made to measure these motions experimentally by incoherent neutron scattering and to quantify them, but with upcoming modern neutron sources and instruments, such models can now be improved. In the present work, we expose a quantitative and exhaustive study of lipid dynamics on DMPC and DMPG membranes, using the Matryoshka model recently developed by our group. The model is confronted here to experimental data collected on two different membrane samples, at three temperatures and two instruments. Despite such complexity, the model describes reliably the data and permits to extract a series of parameters. The results compare also very well to other values found in the literature.

The dynamical Matryoshka model: 3. Diffusive nature of the atomic motions contained in a new dynamical model for deciphering local lipid dynamics

“…The dynamics' parameters of the slow motions of DMPC MLB135 were found to be larger for Regarding the comparison between DMPC MLB135 and DMPC MLV on IN6, it is found that while the τ1 values are similar within the errors, the D1 value and the jump distance are larger for MLVs at 283 K and 311 K. This could be due to the fact that the MLVs are generally more hydrated than MLBs [13]. The present results are also consistent with the results of the EISF/QISF analysis using the Matryoshka model, where the radius of a circle within which the whole lipid molecule can diffuse is larger for MLVs than MLBs [22].…”

“…in the MLB or in the MLV). The τ3 values of d54DMPC MLB135 are larger than those of DMPC MLB135, indicating that the rotational jump diffusion is enhanced for the tail group compared with for the head group, which is consistent with the basic assumption of the Matryoshka model that the tail motions are faster than the head group motions[21,22]. The τ3 values of DMPC MLB45 are found to be larger than those of DMPC MLB135, implying that the fast motions show anisotropy (i.e.…”

“…7 (g) (the τ3 values are tabulated in Tables S1 and S2). The τ3 values of DMPC MLB135 on IN6 and DMPC MLV are found to be independent of the temperature and to be the same within the errors, suggesting that the frequency of the methyl and methylene rotations is independent of the local environments in which they reside The above parameters were allowed to change during the fitting because of their large errors estimated by the EISF/QISF analysis [22]. The fitting results are shown in Fig.…”

“…Details of sample preparations, QENS experiments, and the analysis of the QENS spectra are described in the accompanying papers [21,22]. Briefly, the following samples were used for neutron experiments:…”

“…Based on the dynamical models above, a new theoretical model named Matryoshka model has been presented in the accompanying papers [21,22], where the dynamic structure factor S(Q, ω) is analytically expressed by directly incorporating the scattering functions of various motions that lipid molecules undergo in addition to the decomposition of all the possible motions into three classes, i.e. slow, intermediate, and fast motions.…”