Abstract:
The present study compares and interprets the 1H, 2H, and 13C spin-lattice (T1) relaxation times of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), in the liquid crystalline phase, in terms of models for the molecular dynamics of lipid bilayers. The 1H T1 times of the DPPC bilayer hydrocarbon region at two frequencies and 13C T1 data at seven frequencies, for which the relaxation is dipolar in origin, as well as the 2H T 1 data at three frequencies, due to the quadrupolar interaction, can be unified and interpreted in terms of a collective model for order fluctuations. In normalizing the 13C T1 data to the 1H and 2H T1 values, a vibrationally corrected 13C-1H distance parameter of rCH0=1.14 Å has been assumed, rather than the equilibrium bond length of 1.09 Å. The analysis suggests that the behavior of the individual acyl chain segments of lipid bilayers, in the liquid crystalline phase, is similar to that of molecules in nematic fluids. © 1984 American Institute of Physics.
PMID: 18759470;PMCID: PMC2726791;Abstract:
G-protein-coupled receptors (GPCRs) play key roles in cellular signal transduction and many are pharmacologically important targets for drug discovery. GPCRs can be reconstituted in planar supported lipid bilayers (PSLBs) with retention of activity, which has led to development of GPCR-based biosensors and biochips. However, PSLBs composed of natural lipids lack the high stability desired for many technological applications. One strategy is to use synthetic lipid monomers that can be polymerized to form robust bilayers. A key question is how lipid polymerization affects GPCR structure and activity. Here we have investigated the photochemical activity of bovine rhodopsin (Rhô), a model GPCR, reconstituted into PSLBs composed of lipids having one or two polymerizable dienoyl moieties located in different regions of the acyl chains. Plasmon waveguide resonance spectroscopy was used to compare the degree of Rho photoactivation in fluid and poly(lipid) PSLBs. The position of the dienoyl moiety was found to have a significant effect: polymerization near the glycerol backbone significantly attenuates Rho activity whereas polymerization near the acyl chain termini does not. Differences in cross-link density near the acyl chain termini also do not affect Rho activity. In unpolymerized PSLBs, an equimolar mixture of phosphatidylethanolamine and phosphatidylcholine (PC) lipids enhances activity relative to pure PC; however after polymerization, the enhancement is eliminated which is attributed to stabilization of the membrane lamellar phase. These results should provide guidance for the design of robust lipid bilayers functionalized with transmembrane proteins for use in membrane-based biochips and biosensors. © 2008 American Chemical Society.
In solid-state 2H NMR of fluid lipid bilayers, quasielastic deformations at MHz frequencies are detected as a square-law dependence of the nuclear spin-lattice (R(1Z)) relaxation rates and order parameters (S(CD)). The signature square-law slope is found to decrease progressively with the mole fraction of cholesterol and with the acyl chain length, due to a stiffening of the membrane. The correspondence to thermal vesicle fluctuations and molecular dynamics simulations implies that a broad distribution of modes is present, ranging from the membrane size down to the molecular dimensions.
