Structural Effects of Small Molecules on Phospholipid Bilayers Investigated by Molecular Simulations

We summarize and compare recent Molecular Dynamics simulations on the interactions of dipalmitoylphosphatidylcholine (DPPC) bilayers in the liquid crystalline phase with a number of small molecules including trehalose, a disaccharide of glucose, alcohols, and dimethylsulfoxide (DMSO). The sugar molecules tend to stabilize the structure of the bilayer as they bridge adjacent lipid headgroups. They do not strongly change the structure of the bilayer. Alcohols and DMSO destabilize the bilayer as they increase its area per molecule in the bilayer plane and decrease the order parameter. Alcohols have a stronger detrimental effect than DMSO. The observables which we compare are the area per molecule in the plane of the bilayer, the membrane thickness, and the NMR order parameter of DPPC hydrocarbon tails. The area per molecule and the order parameter are very well correlated whereas the bilayer thickness is not necessarily correlated with them.Comment: 8 pages, 3 figures, accepted to Fluid Phase Equilibri

Intrinsic Structural Features of the Human IRE1α Transmembrane Domain Sense Membrane Lipid Saturation

Activation of inositol-requiring enzyme (IRE1α) is an indispensable step in remedying the cellular stress associated with lipid perturbation in the endoplasmic reticulum (ER) membrane. IRE1α is a single-spanning ER transmembrane protein possessing both kinase and endonuclease functions, and its activation can be fully achieved through the dimerization and/or oligomerization process. How IRE1α senses membrane lipid saturation remains largely unresolved. Using both computational and experimental tools, we systematically investigated the dimerization process of the transmembrane domain (TMD) of IRE1α and found that, with help of the serine 450 residue, the conserved tryptophan 457 residue buttresses the core dimerization interface of IRE1α-TMD. BiFC (bimolecular fluorescence complementation) experiments revealed that mutation on these residues abolished the saturated fatty acid-induced dimerization in the ER membrane and subsequently inactivated IRE1α activity in vivo. Therefore, our results suggest that the structural elements of IRE1α-TMD serve as a key sensor that detects membrane aberrancy

Raman spectroscopic measurements on DEPC liposome : phase transition observation under Xe-gas pressure

Raman spectroscopic analysis was applied to observe the phase transition of dielaidoylphosphatidylcholine (DEPC) liposome under 0.5 MPa Xe pressurization conditions. After the band assignments on DEPC molecule, detailed measurements of the methylene C-H stretching mode spectra were performed. The data revealed that all three peaks associated with DEPC, including the C-H stretching mode,shifted to lower wavenumbers at lower temperatures and that the relative intensities of Raman spectra changed simultaneously. These changes on Raman spectra occurred at approximately 280 K, suggesting a gel to liquid crystalline phase transition. This temperature is lower than that under atmospheric pressure, and it is consistent with DEPC liposomes exposed to Xe measured with differential scanning calorimetric under similar conditions

Micromechanical Cohesion Force between Gas Hydrate Particles Measured under High Pressure and Low Temperature Conditions

To prevent hydrate plugging conditions in the transportation of oil/gas in multiphase flowlines, one of the key processes to control is the agglomeration/deposition of hydrate particles, which are determined by the cohesive/adhesive forces. Previous studies reporting measurements of the cohesive/adhesive force between hydrate particles used cyclopentane hydrate particles in a low-pressure micromechanical force apparatus. In this study, we report the cohesive forces of particles measured in a new high-pressure micromechanical force (MMF) apparatus for ice particles, mixed (methane/ethane, 74.7:25.3) hydrate particles (Structure II), and carbon dioxide hydrate particles (Structure I). The cohesive forces are measured as a function of the contact time, contact force, temperature, and pressure, and determined from pull-off measurements. For the measurements performed of the gas hydrate particles in the gas phase, the determined cohesive force is about 30–35 mN/m, about 8 times higher than the cohesive force of CyC5 hydrates in the liquid CyC5, which is about 4.3 mN/m. We show from our results that the hydrate structure (sI with CO2 hydrates and sII with CH4/C2H6 hydrates) has no influence on the cohesive force. These results are important in the deposition of a gas-dominated system, where the hydrate particles formed in the liquid phase can then stick to the hydrate deposited in the wall exposed to the gas phase

Raman spectra measurements on DEPC liposome and cell membrane of living neuron under xenon pressure

The Raman spectra of liposomes were measured under xenon pressures and low temperatures to observe the spectra changes accompanying the gel to liquid crystalline phase transition of the liposomes. C-H stretching bonds of the lipids in the liposome were slightly red shifted at approximately 285 K and atmospheric pressure, which coincided well with the phase transition condition. This Raman peak shift was observed at lower temperatures and related linearly to the xenon pressures. The xenon pressure dependence on the phase transition temperature was in good agreement with the DSC measurements, and the red shifts of Raman peaks supported the molecular mechanism of interaction between xenon and phospholipid bilayers suggested by the MD simulations. The phase transition measurements under xenon pressure with the microscopic Raman spectroscopy were applied to cultured neuronal networks to observe the interaction of dissolved xenon with the cell membrane and the surrounding water