Different lateral packing stress in acyl chains alters KcsA orientation and structure in lipid membranes.

The molecular structures of the various intrinsic lipids in membranes regulate lipid-protein interactions. These different lipid structures with unique volumes produce different lipid molecular packing stresses/lateral stresses in lipid membranes. Most studies examining lipid packing effects have used phosphatidylcholine and phosphatidylethanolamine (PE), which are the main phospholipids of eukaryotic cell membranes.

DHA-fluorescent probe is sensitive to membrane order and reveals molecular adaptation of DHA in ordered lipid microdomains.

Docosahexaenoic acid (DHA) disrupts the size and order of plasma membrane lipid microdomains in vitro and in vivo. However, it is unknown how the highly disordered structure of DHA mechanistically adapts to increase the order of tightly packed lipid microdomains. Therefore, we studied a novel DHA-Bodipy fluorescent probe to address this issue.

Quantifying the differential effects of DHA and DPA on the early events in visual signal transduction.

A range of evidence from animal, clinical and epidemiological studies indicates that highly polyunsaturated acyl chains play important roles in development, cognition, vision and other aspects of neurological function. In a number of these studies n3 polyunsaturated fatty acids (PUFAs) appear to be more efficacious than n6 PUFAs. In a previous study of retinal rod outer segments obtained from rats raised on either an n3 adequate or deficient diet, we demonstrated that the replacement of 22:6n3 by 22:5n6 in the n3 deficient rats led to functional deficits in each step in the visual signaling process (Niu et al.

Progress in understanding the role of lipids in membrane protein folding.

Detailed investigations of membrane protein folding present a number of serious technical challenges. Most studies addressing this subject have emphasized aspects of protein amino acid sequence and structure. While it is generally accepted that the interplay between proteins and lipids plays an important role in membrane protein folding, the role(s) played by membrane lipids in this process have only recently been explored in any detail.

Contribution of membrane elastic energy to rhodopsin function.

We considered the issue of whether shifts in the metarhodopsin I (MI)-metarhodopsin II (MII) equilibrium from lipid composition are fully explicable by differences in bilayer curvature elastic stress. A series of six lipids with known spontaneous radii of monolayer curvature and bending elastic moduli were added at increasing concentrations to the matrix lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and the MI-MII equilibrium measured by flash photolysis followed by recording UV-vis spectra. The average area-per-lipid molecule and the membrane hydrophobic thickness were derived from measurements of the (2)H NMR order parameter profile of the palmitic acid chain in POPC.

The bacteriorhodopsin carboxyl-terminus contributes to proton recruitment and protein stability.

We examined functional and structural roles for the bacteriorhodopsin (bR) carboxyl-terminus. The extramembranous and intracellular carboxyl-terminus was deleted by insertion of premature translation stop codons. Deletion of the carboxyl-terminus had no effect on purple membrane (PM) lattice dimensions, sheet size, or the electrogenic environment of the ground-state chromophore.

Rhodopsin activity varies in proteoliposomes prepared by different techniques.

A variety of techniques are currently in use for preparing protein-containing lipid vesicles known as proteoliposomes. However, the functionality of membrane protein in proteoliposomes prepared by various techniques has rarely been evaluated directly. We prepared rhodopsin-containing proteoliposomes consisting of asolectin or native retinal rod outer segment disk lipids using n-octyl beta-d-glucopyranoside and the detergent dialysis (DD) and rapid dilution (RD) techniques and measured the activity of rhodopsin using equilibrium UV/vis and flash photolysis spectroscopy.

Lipid-rhodopsin hydrophobic mismatch alters rhodopsin helical content.

The ability of photoactivated rhodopsin to achieve the enzymatically active metarhodopsin II conformation is exquisitely sensitive to bilayer hydrophobic thickness. The sensitivity of rhodopsin to the lipid matrix has been explained by the hydrophobic matching theory, which predicts that lipid bilayers adjust elastically to the hydrophobic length of transmembrane helices. Here, we examined if bilayer thickness adjusts to the length of the protein or if the protein alters its conformation to adapt to the bilayer.

Mitochondrial translocation of alpha-synuclein is promoted by intracellular acidification.

Mitochondrial dysfunction plays a central role in the selective vulnerability of dopaminergic neurons in Parkinson's disease (PD) and is influenced by both environmental and genetic factors. Expression of the PD protein alpha-synuclein or its familial mutants often sensitizes neurons to oxidative stress and to damage by mitochondrial toxins. This effect is thought to be indirect, since little evidence physically linking alpha-synuclein to mitochondria has been reported.

Regulation of membrane proteins by dietary lipids: effects of cholesterol and docosahexaenoic acid acyl chain-containing phospholipids on rhodopsin stability and function.

Purified bovine rhodopsin was reconstituted into vesicles consisting of 1-stearoyl-2-oleoyl phosphatidylcholine or 1-stearoyl-2-docosahexaenoyl phosphatidylcholine with and without 30 mol % cholesterol. Rhodopsin stability was examined using differential scanning calorimetry (DSC). The thermal unfolding transition temperature (T(m)) of rhodopsin was scan rate-dependent, demonstrating the presence of a rate-limited component of denaturation.

Alteration of retinal rod outer segment membrane fluidity in a rat model of Smith-Lemli-Opitz syndrome.

Smith-Lemli-Opitz syndrome (SLOS) is caused by an inherited defect in the last step in cholesterol (Chol) biosynthesis, leading to abnormal accumulation of 7-dehydrocholesterol and decreased Chol levels. Progressive retinal degeneration occurs in an animal model of SLOS, induced by treating rats with AY9944, a selective inhibitor of the enzyme affected in SLOS. Here we evaluated alterations in the biochemical and physical properties of retinal rod outer segment (ROS) membranes in this animal model.

Mitochondrial lipid abnormality and electron transport chain impairment in mice lacking alpha-synuclein.

The presynaptic protein alpha-synuclein, implicated in Parkinson disease (PD), binds phospholipids and has a role in brain fatty acid (FA) metabolism. In mice lacking alpha-synuclein (Snca-/-), total brain steady-state mass of the mitochondria-specific phospholipid, cardiolipin, is reduced 22% and its acyl side chains show a 51% increase in saturated FAs and a 25% reduction in essential n-6, but not n-3, polyunsaturated FAs. Additionally, 23% reduction in phosphatidylglycerol content, the immediate biosynthetic precursor of cardiolipin, was observed without alterations in the content of other brain phospholipids.

Expression of Rem2, an RGK family small GTPase, reduces N-type calcium current without affecting channel surface density.

Rad, Gem/Kir, Rem, and Rem2 are members of the Ras-related RGK (Rad, Gem, and Kir) family of small GTP-binding proteins. Heterologous expression of RGK proteins interferes with de novo calcium channel assembly/trafficking and dramatically decreases the amplitude of currents arising from preexisting high-voltage-activated calcium channels. These effects probably result from the direct interaction of RGK proteins with calcium channel beta subunits.

Effect of packing density on rhodopsin stability and function in polyunsaturated membranes.

Rod outer segment disk membranes are densely packed with rhodopsin. The recent notion of raft or microdomain structures in disk membranes suggests that the local density of rhodopsin in disk membranes could be much higher than the average density corresponding to the lipid/protein ratio. Little is known about the effect of high packing density of rhodopsin on the structure and function of rhodopsin and lipid membranes.

Trans fatty acid derived phospholipids show increased membrane cholesterol and reduced receptor activation as compared to their cis analogs.

The consumption of trans fatty acid (TFA) is linked to the elevation of LDL cholesterol and is considered to be a major health risk factor for coronary heart disease. Despite several decades of extensive research on this subject, the underlying mechanism of how TFA modulates serum cholesterol levels remains elusive. In this study, we examined the molecular interaction of TFA-derived phospholipid with cholesterol and the membrane receptor rhodopsin in model membranes.

Reduced G protein-coupled signaling efficiency in retinal rod outer segments in response to n-3 fatty acid deficiency.

The fatty acid (FA) docosahexaenoic acid (DHA, 22: 6n-3) is highly enriched in membrane phospholipids of the central nervous system and retina. Loss of DHA because of n-3 FA deficiency leads to suboptimal function in learning, memory, olfactory-based discrimination, spatial learning, and visual acuity. G protein-coupled receptor (GPCR) signal transduction is a common signaling motif in these neuronal pathways.

DHA-rich phospholipids optimize G-Protein-coupled signaling.

Objective: To assess the effects of n-3 polyunsaturated phospholipid acyl chains on the initial steps in G-protein-coupled signaling.

Study Design: Isolated components of the visual signal transduction system, rhodopsin, G protein (G(t)), and phosphodiesterase (PDE), were reconstituted in membranes containing various levels of n-3 polyunsaturated phospholipid acyl chains. In addition, rod outer segment disk membranes containing these components were purified from rats raised on n-3-deficient and n-3-adequate diets.

Enhancement of G protein-coupled signaling by DHA phospholipids.

The effect of phospholipid acyl chain and cholesterol composition on G protein-coupled signaling was studied in native rod outer segment (ROS) disk and reconstituted membranes by measuring several steps in the visual transduction pathway. The cholesterol content of disk membranes was varied from 4 to 38 mol% cholesterol with methyl-beta-cyclodextrin. The visual signal transduction system [rhodopsin, G protein (G(t)), and phosphodiesterase (PDE)] was reconstituted with membranes containing various levels of phospholipid acyl chain unsaturation, with and without cholesterol.

Visual acuity and retinal function in infant monkeys fed long-chain PUFA.

Previous randomized clinical trials suggest that supplementation of the human infant diet with up to 0.35% DHA may benefit visual development. The aim of the current study was to assess the impact of including arachidonic acid (AA) and a higher level of DHA in the postnatal monkey diet on visual development.

Retinal sensitivity loss in third-generation n-3 PUFA-deficient rats.

A previous study conducted in guinea pigs suggested that ingestion of diets high in EPA and DHA may result in suboptimal retinal function. The aim of the present study was to evaluate retinal function in pigmented (Long-Evans) rats, raised to a third generation on diets that were either deficient in n-3 PUFA or adequate (with the addition of DHA). Electroretinographic assessment employed full-field white flash stimulation.

Structure and orientation of a G protein fragment in the receptor bound state from residual dipolar couplings.

Residual dipolar couplings for a ligand that is in fast exchange between a free state and a state where it is bound to a macroscopically ordered membrane protein carry precise information on the structure and orientation of the bound ligand. The couplings originate in the bound state but can be detected on the free ligand using standard high resolution NMR. This approach is used to study an analog of the C-terminal undecapeptide of the alpha-subunit of the heterotrimeric G protein transducin when bound to photo-activated rhodopsin.

n-3 fatty acid deficiency alters recovery of the rod photoresponse in rhesus monkeys.

Purpose: Docosahexaenoic acid (DHA) is the major polyunsaturated fatty acid within rod outer segments. Varying the dietary content of DHA or its precursor, alpha-linolenic acid (ALA), can alter retinal DHA levels. The purpose of the present study was to assess rod phototransduction and recovery in rhesus monkeys raised on diets with different DHA and ALA content.

Manipulation of cholesterol levels in rod disk membranes by methyl-beta-cyclodextrin: effects on receptor activation.

The effect of cholesterol on rod outer segment disk membrane structure and rhodopsin activation was investigated. Disk membranes with varying cholesterol concentrations were prepared using methyl-beta-cyclodextrin as a cholesterol donor or acceptor. Cholesterol exchange followed a simple equilibrium partitioning model with a partition coefficient of 5.