Determination of the partition coefficients of the nonionic detergent C12E7 between lipid-detergent mixed membranes and water by means of Laurdan fluorescence spectroscopy

The membrane-water partition coefficient of the detergent C₁₂E₇ between water and C₁₂E₇/POPC mixed membranes has been determined by means of steady-state fluorescence spectroscopy. The emission spectra of the fluorescent probe Laurdan were used as an indicator of membrane composition at different membrane concentrations in the sample. The partition coefficient expressed as the ratio of the mole fractions of the detergent in the membrane and water phases is about 6^*10⁵ at low molar ratios of C₁₂E₇/POPC (R _c ) and decreases rapidly with increasingR _c . The limiting detergent content of the lamellar phase (R _c ^* >0.8) is indicated by a minimum ofP(R _c ).     

Performance of the general amber force field in modeling aqueous POPC membrane bilayers

The aim of this work was to answer the question of whether the general amber force field (GAFF) is good enough to simulate fully hydrated POPC membrane bilayers. The test system contained 128 POPC and 2985 TIP3P water molecules. The equilibration was carried out in a nonarbitrary manner to reach the stable liquid-crystalline phase. The simulations were performed by using particle mesh Ewald electrostatics implemented in molecular dynamics packages Amber8 (NPT ensembles) and NAMD2 (NPgammaT ensembles). The computational results were assessed against the following experimental membrane properties: (i) area per lipid, (ii) area compressibility modulus, (iii) order parameter, (iv) gauche conformations per acyl chain, (v) lateral diffusion coefficients, (vi) electron density profile, and (vii) bound water at the lipid/water interface. The analyses revealed that the tested force field combination approximates the experimental values at an unexpectedly good level when the NPgammaT ensemble is applied with a surface tension of 60 mN m(-1) per bilayer. It is concluded that the GAFF/TIP3P combination can be utilized for aqueous membrane bilayer simulations, as it provides acceptable accuracy for biomolecular modeling.     

多巴胺在POPC磷脂双层膜中扩散和透过过程的分子动力学模拟

多巴胺作为脑组织内一种重要的神经递质在细胞膜内外需要做合适的迁移,发挥其功能. 多巴胺在细胞膜中扩散和透过过程的分子动力学涉及到多巴胺分子保护通道的畅通,与精神分裂症等病症有关. 本文采用1-棕榈酰-2-油酰-卵磷脂(POPC)双层膜模拟细胞膜,通过分子动力学模拟获得多巴胺分子在细胞膜中和透过细胞膜运动自由能变化,探讨多巴胺在细胞膜中扩散和透过过程的分子动力学. 多巴胺分子在POPC磷脂双层膜中间层做扩散运动的自由能变化为10-54 kJ·mol^-1 (310 K),显示多巴胺分子在细胞膜中间层很容易横向和纵向扩散,保持多巴胺保护通道的畅通. 多巴胺分子不容易透过POPC磷脂双层膜,因为透过过程自由能能垒为117-125 kJ·mol^-1 (310 K). 因此,人脑组织神经细胞里生产的多巴胺分子可以储藏在生物细胞膜空间. 而过量的多巴胺则可以通过保护通道进入磷脂双层膜结构中间,做横向和纵向扩散运动,并且透过细胞膜,避免精神分裂症的发生. 生物细胞膜的正常功能对于保持多巴胺保护通道的畅通和避免精神分裂症的出现都是重要的. 研究结果与其它实验观察和结果相一致.     

甲基多巴透过POPC磷脂双层膜过程的分子动力学模拟

采用分子动力学模拟研究甲基多巴分子透过磷脂双层膜的动力学机制.研究所采用的磷脂双层膜是一种卵磷脂脂质分子双层膜,即1-棕榈酰-2-油酰-卵磷脂(POPC)双层膜,分子动力学模拟基于Gromacs程序.通过分子动力学模拟获得甲基多巴透过POPC双层膜的自由能垒是99.9 kJ·mol-1(310 K),显示甲基多巴分子可以透过细胞生物膜.模拟获得甲基多巴在POPC双层膜中间层扩散运动的自由能垒是16.9-27.7 kJ·mol-1(310 K),证明甲基多巴分子在细胞膜中间层容易扩散.研究工作加深了对甲基多巴治疗高血压病机制的理解,促进研发治疗高血压病的新药物.     

Synthesis and Characterization of Multifunctional Nanovesicles Composed of POPC Lipid Molecules for Nuclear Imaging

The integration of nuclear imaging analysis with nanomedicine has tremendously grown and represents a valid and powerful tool for the development and clinical translation of drug delivery systems. Among the various types of nanostructures used as drug carriers, nanovesicles represent intriguing platforms due to their capability to entrap both lipophilic and hydrophilic agents, and their well-known biocompatibility and biodegradability. In this respect, here we present the development of a labelling procedure of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine)-based liposomes incorporating an ad hoc designed lipophilic NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) analogue, derivatized with an oleic acid residue, able to bind the positron emitter gallium-68(III). Based on POPC features, the optimal conditions for liposome labelling were studied with the aim of optimizing the Ga(III) incorporation and obtaining a significant radiochemical yield. The data presented in this work demonstrate the feasibility of the labelling procedure on POPC liposomes co-formulated with the ad hoc designed NOTA analogue. We thus provided a critical insight into the practical aspects of the development of vesicles for theranostic approaches, which in principle can be extended to other nanosystems exploiting a variety of bioconjugation protocols.     

Cholesterol Alters the Phase Separation in Model Membranes Containing hBest1

Human retinal pigment epithelial (RPE) cells express the transmembrane Ca²⁺-dependent Cl⁻ channel bestrophin-1 (hBest1) of the plasma membrane. Mutations in the hBest1 protein are associated with the development of distinct pathological conditions known as bestrophinopathies. The interactions between hBest1 and plasma membrane lipids (cholesterol (Chol), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and sphingomyelin (SM)) determine its lateral organization and surface dynamics, i.e., their miscibility or phase separation. Using the surface pressure/mean molecular area (π/A) isotherms, hysteresis and compressibility moduli (C_s⁻¹) of hBest1/POPC/Chol and hBest1/SM/Chol composite Langmuir monolayers, we established that the films are in an LE (liquid-expanded) or LE-LC (liquid-condensed) state, the components are well-mixed and the Ca²⁺ ions have a condensing effect on the surface molecular organization. Cholesterol causes a decrease in the elasticity of both films and a decrease in the ΔG_mix^π values (reduction of phase separation) of hBest1/POPC/Chol films. For the hBest1/SM/Chol monolayers, the negative values of ΔG_mix^π are retained and equalized with the values of ΔG_mix^π in the hBest1/POPC/Chol films. Shifts in phase separation/miscibility by cholesterol can lead to changes in the structure and localization of hBest1 in the lipid rafts and its channel functions.     

甲基多巴透过POPC磷脂双层膜过程的分子动力学模拟

采用分子动力学模拟研究甲基多巴分子透过磷脂双层膜的动力学机制. 研究所采用的磷脂双层膜是一种卵磷脂脂质分子双层膜,即1-棕榈酰-2-油酰-卵磷脂（POPC）双层膜,分子动力学模拟基于Gromacs程序. 通过分子动力学模拟获得甲基多巴透过POPC双层膜的自由能垒是99.9 kJ·mol^-1（310 K）,显示甲基多巴分子可以透过细胞生物膜. 模拟获得甲基多巴在POPC双层膜中间层扩散运动的自由能垒是16.9-27.7 kJ·mol^-1（310 K）,证明甲基多巴分子在细胞膜中间层容易扩散. 研究工作加深了对甲基多巴治疗高血压病机制的理解,促进研发治疗高血压病的新药物.     

Adsorption of DNA onto anionic lipid surfaces

Currently self-assembled DNA delivery systems composed of DNA multivalent cations and anionic lipids are considered to be promising tools for gene therapy. These systems become an alternative to traditional cationic lipid–DNA complexes because of their low cytotoxicity lipids. However, currently these nonviral gene delivery methods exhibit low transfection efficiencies. This feature is in large part due to the poorly understood DNA complexation mechanisms at the molecular level. It is well-known that the adsorption of DNA onto like charged lipid surfaces requires the presence of multivalent cations that act as bridges between DNA and anionic lipids. Unfortunately, the molecular mechanisms behind such adsorption phenomenon still remain unclear. Accordingly a historical background of experimental evidence related to adsorption and complexation of DNA onto anionic lipid surfaces mediated by different multivalent cations is firstly reviewed. Next, recent experiments aimed to characterise the interfacial adsorption of DNA onto a model anionic phospholipid monolayer mediated by Ca^2 + (including AFM images) are discussed. Afterwards, modelling studies of DNA adsorption onto charged surfaces are summarised before presenting preliminary results obtained from both CG and all-atomic MD computer simulations. Our results allow us to establish the optimal conditions for cation-mediated adsorption of DNA onto negatively charged surfaces. Moreover, atomistic simulations provide an excellent framework to understand the interaction between DNA and anionic lipids in the presence of divalent cations. Accordingly,our simulation results in conjunction go beyond the macroscopic picture in which DNA is stuck to anionic membranes by using multivalent cations that form glue layers between them. Structural aspects of the DNA adsorption and molecular binding between the different charged groups from DNA and lipids in the presenceof divalent cations are reported in the last part of the study. Although this research work is far from biomedical applications, we truly believe that scientific advances in this line will assist, at least in part, in the rationaldesign and development of optimal carrier systems for genes and applicable to other drugs.     

Computational investigation of lipid hydration water of Lα 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine at three hydration levels

Atomistic-scale simulations of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid bilayer systems were performed at three hydration levels from 12 water per lipid to 41 water per lipid. The structural and dynamical properties of water at each hydration level are the focus of the current study. The water properties are reported as a function of slab position relative to the lipid central plane using a floating slab model. Water properties depend more strongly on the relative slab position to the lipid than on the hydration level of the lipid. Water hydrogen bonds strengthen as water enters into the lipid, reaching a maximum at the phosphorus density maximum. The ratio of lateral and normal diffusion coefficients of water varies as water enters into the lipid and demonstrates an interesting crossover phenomenon at the phosphorus density maximum regardless of the overall hydration level. While most properties do not change beyond the commonly established excess water point, the water diffusion coefficient still increases upon further hydration. We propose a scheme that classifies lipid hydration water into buried water, interface water, and bulk-like water.     

The effect of the ionophore valinomycin on biomimetic solid supported lipid DPPTE/EPC membranes

Self assembled monolayers and bilayers are produced on a flat glass surface, bound by a thiolipid onto bare gold. 1,2-Dipalmitoyl-sn-Glycero-3-Phosphothioethanol (DPPTE) is used as the molecule binding to the electrode surface. The lipid lambda-alpha-Phosphatidyl-Choline-beta-Oleoyl-g-Palmitoyl (POPC) and the lipid mixture eggphosphatadiylcholine (EPC) are used as spacer lipids with the aim of achieving solid-supported artificial lipid membranes. With the aim of creating and investigating more natural systems, ion carrier proteins such as valinomycin are introduced into the DPPTE/EPC system. The direct influence on the membranes as well as the effects of different ionic solutions on the proteins is shown.