Orientation of the benzophenone group at various depths in bilayers
摘要:
The hydrophobic core of biological membranes is primarily composed of fatty acyl chains of lipids and side chains of nonpolar amino acids belonging to membrane-spanning domains of transmembrane proteins. Electron transport across the 35-40-angstrom membrane dielectric takes place via suitably oriented electron-transfer groups associated with transmembrane domains of membrane-bound proteins. We propose here that the design of lipids bearing electron-transport groups oriented at different depths can provide the necessary supramolecular assembly in the form of a monolayer or a bilayer to carry out electron transfer. The design of these modified lipids is crucial to the success of such a molecular device. We report here the design and synthesis of three benzophenone-based phospholipids capable of orienting the benzophenone group at different depths in a bilayer. The orientation of the benzophenone group was determined by photochemical cross-linking of these lipids with dimyristoylphosphatidylcholine in single bilayer vesicles followed by mass spectral analyses of the cross-linked products. The actual site of cross-linking on the myristoyl chain was determined, and it was observed that a range of carbon atoms are functionalized. The range of carbon atoms functionalized was found to be centered around the position expected from the transverse location of the benzophenone-based phospholipid in the bilayer. The data could be best interpreted in terms of zones of carbon atoms functionalized rather than any discreet site. This is in keeping with the current models of membranes which suggest the presence of a fluid gradient as one goes down the fatty acyl chain in the membrane. However, the range of carbon atoms functionalized was narrowed with probes reported here. The use of a hydrophobic tail attached to the benzophenone group assisted in directing the orientation of the photoactive group at different depths. Besides providing an effective design strategy for the orientation of electron-transfer groups at different depths in a bilayer, the high insertion yield and the depth-dependent labeling observed in artificial membranes suggest that the benzophenone-based phospholipids reported here could also prove useful for studying the structure of single and multiple spanning transmembrane proteins.
Hydration and Hydrogen Bonding of Carbonyls in Dimyristoyl-Phosphatidylcholine Bilayer
作者:Victor V. Volkov、Francesca Nuti、Yuji Takaoka、Riccardo Chelli、Anna Maria Papini、Roberto Righini
DOI:10.1021/ja0614621
日期:2006.7.1
We combine two-color ultrafast infrared spectroscopy and molecular dynamics simulation to investigate the hydration of carbonyl moieties in a dimyristoyl-phosphatidylcholine bilayer. Excitation with femtosecond infrared pulses of the OD stretching mode of heavy water produces a time dependent change of the absorption band of the phospholipid carbonyl groups. This intermolecular vibrational coupling
我们结合双色超快红外光谱和分子动力学模拟来研究二肉豆蔻酰-磷脂酰胆碱双层中羰基部分的水合作用。用重水的 OD 拉伸模式的飞秒红外脉冲激发产生磷脂羰基吸收带的时间依赖性变化。这种分子间振动耦合影响整个 C=O 带,因此表明磷脂膜中羰基红外响应的光学不均匀性不能归因于水合作用的变化。实验和理论结果都表明,与 sn-2 相比,sn-1 羰基与水形成氢键的倾向更高。时间分辨实验允许跟踪系统从 OD 拉伸模式中的非平衡能量局部化到热平衡条件的演变,并提供该过程的特征时间常数。该方法为研究膜、聚合物、蛋白质和玻璃等复杂系统中的分子间结构关系开辟了新的机会。
Sterol-Modified Phospholipids: Cholesterol and Phospholipid Chimeras with Improved Biomembrane Properties
作者:Zhaohua Huang、Francis C. Szoka
DOI:10.1021/ja8065557
日期:2008.11.19
We synthesized a family of sterol-modified glycerophospholipids (SML) in which the sn-1 or sn-2 position is covalently attached to cholesterol and the alternative position contains an aliphatic chain. The SML were used to explore how anchoring cholesterol to a phospholipid affects cholesterol behavior in a bilayer. Notably, cholesterol in the SML retains the membrane condensing properties of free cholesterol regardless of the chemistry or position of its attachment to the glycerol moiety of the phospholipid. SMLs by themselves formed liposomes upon hydration and in mixtures between an SML and diacylglycerophospholipids (C14 to C18 chain length) the thermotropic phase transition is eliminated at the SML equivalent of about 30 mol % free cholesterol. Osmotic-induced contents leakage from SML (C14-C18) liposomes depends upon the linkage and position of cholesterol but in general is similar to that observed in 3/2 diacylphosphatidylcholine/cholesterol (mole ratio) liposomes. SML liposomes are exceptionally resistant to contents release in the presence of serum at 37 degrees C. This is probably due to the fact that SML exchange between bilayers is more than 100 fold less than the exchange rate of free cholesterol in the same conditions. Importantly, SML liposomes containing doxorubicin are as effective in treating the murine C26 colon carcinoma as Doxil, a commercial liposome doxorubicin formulation. SMLs stabilize bilayers but do not exchange and hence provide a new tool for biophysical studies on membranes. They may improve liposomal drug delivery in organs predisposed to the extraction of free cholesterol from bilayers, such as the skin, lung, or blood.
Polymer-Supported Bases. XII. Regioselective Synthesis of Lysophospholipids Using Polymer-Supported Bicyclic Amidines or Guanidines
作者:Y. Tamura、W. Fukuda、M. Tomoi、S. Tokuyama
DOI:10.1080/00397919408010612
日期:1994.11
1-Acylphosphatidylcholines were prepared in good yields by the regioselective monoacylation of L-alpha-glycerophosphorylcholine with acylimidazoles in the presence of polymer-supported bicyclic amidine of guanidine.