Transfer of cholestane spin label between lipid bilayer membranes and its molecular motion in membranes

Structure and dynamics of polyunsaturated hydrocarbon chains in lipid bilayers-significance for GPCR function

This review summarizes results of our recent solid-state NMR investigations on polyunsaturated 18:0-22:6n3-PC/PE/PS and 18:0-22:5n6-PC bilayers. Data on structure and dynamics of the polyunsaturated docosahexaenoyl (DHAn3, 22:6n3) and docosapentaenoyl chains (DPAn6, 22:5n6), investigated at physiological conditions, are reported. Lipid-protein interaction was studied on reconstituted bilayers containing the G-protein coupled membrane receptor (GPCR) rhodopsin as well as on rod outer segment (ROS) disk membranes prepared from bovine retinas. Results reveal surprisingly rapid conformational transitions of polyunsaturated chains and existence of weakly specific interactions of DHAn3 with spatially distinct sites on rhodopsin.

Application of in vivo ESR spectroscopy to measurement of cerebrovascular ROS generation in stroke

This study used an in vivo ESR spectroscopy/spin probe technique to measure directly the generation of reactive oxygen species (ROS) in the brain after cerebral ischemia-reperfusion. Transient middle cerebral artery occlusion (MCAO) was induced in rats by inserting a nylon thread into the internal carotid artery for 1 h. The in vivo generation of ROS and its location in the brain were analyzed from the enhanced ESR signal decay data of three intra-arterially injected spin probes with different membrane permeabilities. The ESR signal decay of the probe with intermediate permeability was significantly enhanced 30 min after reperfusion following MCAO, whereas no enhancement was observed with the other probes or in the control group. The enhanced in vivo signal decay was significantly suppressed by superoxide dismutase (SOD). Brain damage was barely discernible until 3 h of reperfusion, and was clearly suppressed with the probe of intermediate permeability. The antioxidant MCI-186 completely suppressed the enhanced in vivo signal decay after transient MCAO. These results clearly demonstrate that ROS are generated at the interface of the cerebrovascular cell membrane when reperfusion follows MCAO in rats, and that the ROS generated during the initial stages of transient MCAO cause brain injury.

Influence of docosahexaenoic acid and cholesterol on lateral lipid organization in phospholipid mixtures

We investigated lateral lipid organization in membranes with a lipid composition relevant to neural and retinal membranes [phosphatidylcholine (PC)/phosphatidylethanolamine (PE)/phosphatidylserine (PS)/cholesterol, 4/4/1/1, mol/mol/mol/mol]. The mixed-chain phospholipids contained saturated stearic acid (18:0) in the sn-1 position and the monounsaturated oleic acid (18:1) or polyunsaturated docosahexaenoic acid (22:6) in sn-2. Lateral lipid organization was evaluated by 2H NMR order parameter measurements on stearic acid of all individual types of phospholipids in the mixture and, through a novel approach, two-dimensional NOESY 1H NMR spectroscopy with magic angle spinning (MAS). The docosahexaenoic acid chain order was evaluated from 1H NMR chain signal MAS-sideband intensities. Averaged over all lipids, the cholesterol-induced increase in sn-1 chain order is 2-fold larger in monounsaturated than in polyunsaturated lipids, and the order of both saturated and polyunsaturated hydrocarbon chains increases. Addition of cholesterol increases lipid order in the sequence 18:0-18:1 PE > 18:0-18:1 PC > 18:0-18:1 PS for the monounsaturated and 18:0-22:6 PC >> 18:0-22:6 PE > 18:0-22:6 PS for polyunsaturated mixtures. The variation of order parameters between lipid species suggests that cholesterol induces the formation of lipid microdomains with a headgroup and chain unsaturation-dependent lipid composition. The preferential interaction between cholesterol and polyunsaturated 18:0-22:6 PC, followed by 18:0-22:6 PE and 18:0-22:6 PS, was confirmed by 1H MAS NOESY cross-relaxation rate differences. Furthermore, cholesterol preferentially associates with saturated chains in mixed-chain lipids reflected by higher saturated chain-to-cholesterol cross-relaxation rates. We propose that cholesterol forms PC-enriched microdomains in the polyunsaturated 18:0-22:6 PC/18:0-22:6 PE/18:0-22:6 PS/cholesterol membranes in which the saturated sn-1 chains are preferentially oriented toward the cholesterol molecules.

Dynamic properties of the haptenic site of lipid haptens in phosphatidylcholine membranes. Their relation to the phase transition of the host lattice

The relation between the dynamic properties of the haptenic site of lipid haptens and the phase transition of the host lattice was investigated using head group spin-labeled phosphatidylethanolamines, that is, spin-label lipid haptens (Brûlet, P., and H. M. McConnell, 1976, Proc. Natl. Acad. Sci. USA., 73:2977-2981; Brûlet, P., and H. M. McConnell, 1977, Biochemistry, 16:1209-1217). The electron spin resonance (ESR) spectra of the lipid haptens in liposomal membranes showed three narrow resonance lines, whose widths and hyperfine splitting values suggested that the haptenic site, i.e., the spin-label moiety, should be exposed in the water phase. The line width of each peak depended on the host lipid species and on the incubation temperature. A temperature study using dipalmitoylphosphatidylcholine (DPPC) liposomes showed that the dynamic properties of the haptenic site were related to the main phase transition and the subphase transition of the host lattice but not to the prephase transition. The angular amplitudes of the tumbling motion of the haptenic site were estimated using oriented multibilayer systems. The angular amplitude of dipalmitoyl-phosphatidyl-N-[[N-(1-oxyl-2,2,6, 6-tetramethyl-4-piperidinyl)-carbamoyl]-methyl]-ethanolamine in DPPC membranes was 63 degrees at 2 degrees C, and it increased slightly with an increase in temperature regardless of the phase transition of the host lattice. The value for egg phosphatidylcholine (PC) at 25 degrees C was the same as for DPPC above its main phase transition temperature. Rotational correlation time analysis showed that the axial rotation of the haptenic site was preferable to the tumbling motion of the rotational axis, and the predominance depended on the phase transition, Lc----L beta' and P beta'----L alpha. Elongation of the spacer arm between the haptenic site and phosphate increased the angular amplitude of the tumbling motion but reduced the effect of the host lattice. Spin-label lipid haptens with unsaturated fatty acyl chains were distributed heterogeneously in DPPC membranes, whereas those with the same fatty acyl chain as the host lattice were distributed randomly. The ESR spectrum of a lipid hapten under its prephase transition temperature showed two components, broad and narrow. This suggests that at least two different domains, a hapten-rich domain and a hapten-poor one, may coexist in membranes. ESR measurements at various temperatures suggested that the haptenic site fraction in the hapten-rich domain decreased in part during the phase transition from L beta' to P beta', and disappeared completely in the La phase. The spatial mobility and lateral diffusion of lipid haptens will be discussed in greater detail.

ACTH stimulation on cholesterol side chain cleavage activity of adrenocortical mitochondria. Transfer of the stimulus from plasma membrane to mitochondria

Adrenocortical mitochondrial cholesterol side chain cleavage reactions are regulated by the influence of pituitary ACTH. The mechanism of the stimulation involves adenyl cyclase, cAMP-dependent protein kinase, cholesterol esterase, and ribosomal labile protein synthesis. Through these reactions the stimulus reaches the mitochondrial side chain cleavage enzyme system. In this review article, the current implications on the stimulus transfer from the plasma membrane to the mitochondrial inner membrane are summarized. In particular the availability of cholesterol to P-450scc was discussed in terms of the distribution of cholesterol molecules in the membranes.