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Klaus Gawrisch

Publications and source records attributed to Klaus Gawrisch.

At least 19 recordsLinked to original sources
PubMed2006

Use of dual affinity tags for expression and purification of functional peripheral cannabinoid receptor.

The human peripheral cannabinoid receptor (CB2) was expressed as a fusion with the maltose-binding protein (at the N-terminus), thioredoxin A (at the C-terminus) and two small affinity tags (a Strep-tag and a polyhistidine tag). Expression levels of the recombinant receptor in Escherichia coli BL21(DE3) cells were dependent on location and type of tags in the expression construct, and were as high as 1-2mg per liter of bacterial culture. The recombinant receptor was ligand binding-competent, and activated cognate G-proteins in an in vitro coupled assay. The fusion CB2-125 protein was purified by immobilized metal affinity chromatography on a Ni-NTA resin. Maltose-binding protein, thioredoxin and a decahistidine tag were removed from the fusion by treatment with Tobacco etch virus (Tev) protease. Purification to over 90% homogeneity of the resulting CB2, containing an N-terminal Strep-tag was achieved by affinity chromatography on a StrepTactin resin. Circular dichroism spectroscopy indicated an alpha-helical content of the purified recombinant protein of approximately 54%. The expression and purification protocol allows for production of large (milligram) quantities of functional peripheral cannabinoid receptor, suitable for subsequent structural characterization. Preliminary results of reconstitution experiments indicate that the CB2 has retained its ligand-binding properties.

Affinity Labels↗
PubMed2006

Functional reconstitution of rhodopsin into tubular lipid bilayers supported by nanoporous media.

We report on a novel reconstitution method for G-protein-coupled receptors (GPCRs) that yields detergent-free, single, tubular membranes in porous anodic aluminum oxide (AAO) filters at concentrations sufficient for structural studies by solid-state NMR. The tubular membranes line the inner surface of pores that traverse the filters, permitting easy removal of detergents during sample preparation as well as delivery of ligands for functional studies. Reconstitution of bovine rhodopsin into AAO filters did not interfere with rhodopsin function. Photoactivation of rhodopsin in AAO pores, monitored by UV-vis spectrophotometry, was indistinguishable from rhodopsin in unsupported unilamellar liposomes. The rhodopsin in AAO pores is G-protein binding competent as shown by a [35S]GTPgammaS binding assay. The lipid-rhodopsin interaction was investigated by 2H NMR on sn-1- or sn-2-chain perdeuterated 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phospholine as a matrix lipid. Rhodopsin incorporation increased mosaic spread of bilayer orientations and contributed to spectral density of motions with correlation times in the range of nano- to microseconds, detected as a significant reduction in spin-spin relaxation times. The change in lipid chain order parameters due to interaction with rhodopsin was insignificant.

Aluminum Oxide↗
PubMed2006

Evidence for specificity in lipid-rhodopsin interactions.

The interaction of bovine rhodopsin with poly- and monounsaturated lipids was studied by (1)H MAS NMR with magnetization transfer from rhodopsin to lipid. Experiments were conducted on bovine rod outer segment (ROS) disks and on recombinant membranes containing lipids with polyunsaturated, docosahexaenoyl (DHA) chains. Poly- and monounsaturated lipids interact specifically with different sites on the rhodopsin surface. Rates of magnetization transfer from protein to DHA are lipid headgroup-dependent and increased in the sequence PC < PS < PE. Boundary lipids are in fast exchange with the lipid matrix on a time scale of milliseconds or shorter. All rhodopsin photointermediates transferred magnetization preferentially to DHA-containing lipids, but highest rates were observed for Meta-III rhodopsin. The experiments show clearly that the surface of rhodopsin has sites for specific interaction with lipids. Current theories of lipid-protein interaction do not account for such surface heterogeneity.

Animals↗
PubMed2006

Bacterial expression of functional, biotinylated peripheral cannabinoid receptor CB2.

A biotin-protein ligase recognition site (BRS) was inserted into a polypeptide comprised of the maltose-binding protein, the peripheral cannabinoid receptor (CB2), thioredoxin A, and a polyhistidine tag at the carboxy terminus. Expression levels of the recombinant receptor in Escherichia coli BL21(DE3) cells were approximately 1mg per liter of bacterial culture. The biotinylated CB2-fusion fully retained its ligand-binding capacity. Introduction of the BRS at the C-terminus of the CB2 fusion protein (construct CB2-109) resulted in its complete in vivo biotinylation; the biotinylated protein was streptavidin-binding competent. Positioning of the BRS near the N-terminus of CB2 (CB2-112) resulted in a very low level of biotinylation in vivo. However, the detergent solubilized and purified CB2-112 fusion protein were successfully biotinylated in vitro by action of a BirA biotin-protein ligase. The biotinylated CB2-112 fusion protein was cleaved by the tobacco etch virus protease at specifically inserted sites, and deposited onto monomeric avidin agarose beads. Biotinylation of the recombinant CB2 receptor enabled not only purification but also immobilization of the GPCR on a solid support in homogeneous orientation which is beneficial for subsequent structural characterization.

Binding, Competitive↗
PubMed2006

Closed-loop miscibility gap and quantitative tie-lines in ternary membranes containing diphytanoyl PC.

Vesicles containing ternary mixtures of diphytanoylphosphatidylcholine, dipalmitoylphosphatidylcholine (DPPC), and cholesterol produce coexisting liquid phases over an unusually large range of temperature and composition. Liquid domains persist well above the DPPC chain melting temperature (41 degrees C), resulting in a closed-loop miscibility gap bounded by two critical points at fixed temperature. Quantitative tie-lines are determined directly from 2H NMR spectra using a novel analysis, and are found to connect a liquid-disordered phase rich in diphytanoyl PC with a liquid-ordered phase rich in DPPC. The direction of the tie-lines implies that binary DPPC/cholesterol mixtures are in one uniform phase above 41 degrees C. All 2H NMR results for tie-lines are verified by independent fluorescence microscopy results.

Cholesterol↗
PubMed2006

The physical chemistry of biological membranes.

Physical chemistry explains the principles of self-organization of lipids into bilayers that form the matrix of biological membranes, and continuum theory of membrane energetics is successful in explaining many biological processes. With increasing sophistication of investigative tools, there is now a growing appreciation for lipid diversity and for the role of individual lipids and specific lipid-protein interactions in membrane structure and function.

Animals↗
PubMed2005

Characterization of the liquid-ordered state by proton MAS NMR.

We investigated if magic angle spinning (MAS) 1H NMR can be used as a tool for detection of liquid-ordered domains (rafts) in membranes. In experiments with the lipids SOPC, DOPC, DPPC, and cholesterol we demonstrated that 1H MAS NMR spectra of liquid-ordered domains (lo) are distinctly different from liquid-disordered (ld) and solid-ordered (so) membrane regions. At a MAS frequency of 10 kHz the methylene proton resonance of hydrocarbon chains in the ld phase has a linewidth of 50 Hz. The corresponding linewidth is 1 kHz for the lo phase and several kHz for the so phase. According to results of 1H NMR dipolar echo spectroscopy, the broadening of MAS resonances in the lo phase results from an increase in effective strength of intramolecular proton dipolar interactions between adjacent methylene groups, most likely because of a lower probability of gauche/trans isomerization in lo. In spectra recorded as a function of temperature, the onset of lo domain (raft) formation is seen as a sudden onset of line broadening. Formation of small domains yielded homogenously broadened resonance lines, whereas large lo domains (diameter >0.3 microm) in an ld environment resulted in superposition of the narrow resonances of the ld phase and the much broader resonances of lo. 1H MAS NMR may be applied to detection of rafts in cell membranes.

Cholesterol↗
PubMed2005

The structure of polyunsaturated lipid bilayers important for rhodopsin function: a neutron diffraction study.

The structure of oriented 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine bilayers with perdeuterated stearoyl- or docosahexaenoyl hydrocarbon chains was investigated by neutron diffraction. Experiments were conducted at two different relative humidities, 66 and 86%. At both humidities we observed that the polyunsaturated docosahexaenoyl chain has a preference to reside near the lipid water interface. That leaves voids in the bilayer center that are occupied by saturated stearoyl chain segments. This uneven distribution of saturated- and polyunsaturated chain densities is likely to result in membrane elastic stress that modulates function of integral receptor proteins like rhodopsin.

Biophysics↗
PubMed2005

Specific volumes of unsaturated phosphatidylcholines in the liquid crystalline lamellar phase.

The specific volumes of seven 1,2-diacyl-sn-glycero-3-phosphocholines with symmetric, unbranched acyl chains containing one, four, or six cis double bonds per chain, or with a saturated sn-1 chain and one, four, or six cis double bonds in the sn-2 chain were determined by the neutral buoyancy method. Experiments were conducted in the liquid crystalline lamellar phase over the temperature range from 5 to 35 degrees C. It is demonstrated that the molecular volume of phosphatidylcholines can be well approximated as the sum of a constant volume of the polar lipid head region and the temperature-dependent volumes of hydrocarbon chain CH2, CH, and terminal CH3 groups. A linear dependence of chain segment volumes on temperature was observed. A self-consistent set of partially temperature-dependent volumes is obtained that allows prediction of phosphatidylcholine molecular volumes within very tight error margins.

Chemical Phenomena↗
PubMed2005

Diffusion of cholesterol and its precursors in lipid membranes studied by 1H pulsed field gradient magic angle spinning NMR.

Cholesterol content is critical for membrane functional properties. We studied the influence of cholesterol and its precursors desmosterol and lanosterol on lateral diffusion of phospholipids and sterols by1H pulsed field gradients (PFG) magic angle spinning (MAS) NMR spectroscopy. The high resolution of resonances afforded by MAS NMR permitted simultaneous diffusion measurements on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and sterols. The cholesterol diffusion mirrored the DPPC behavior, but rates were slightly higher at all cholesterol concentrations. DPPC and cholesterol diffusion rates decreased and became cholesterol concentration dependent with the onset of liquid-ordered phase formation. The activation energies of diffusion in the coexistence region of liquid-ordered/liquid-disordered phases are higher by about a factor of 2 compared to pure DPPC and to the pure liquid-ordered state formed at higher cholesterol concentrations. We assume that the higher activation energies are a reflection of lipid diffusion across domain boundaries. In lanosterol- and desmosterol-containing membranes, the DPPC and sterol diffusion coefficients are somewhat higher. Whereas the desmosterol rates are only slightly higher than those of DPPC, the lanosterol diffusion rates significantly exceed DPPC rates, indicating a weaker interaction between DPPC and lanosterol.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2005

Electrostatic contributions to indole-lipid interactions.

The role of electrostatic forces in indole-lipid interactions was studied by (1)H and (2)H NMR in ether- and ester-linked phospholipid bilayers with incorporated indole. Indole-ring-current-induced (1)H NMR chemical shifts of lipid resonances in bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, 1,2-dioleoyl-sn-glycero-3-phosphocholine, 1,2-di-O-octadecenyl-sn-glycero-3-phosphocholine, and 1,2-di-O-octadecenyl-sn-glycero-3-phosphomethanol show a bimodal indole distribution, with indole residing at the upper hydrocarbon chain/glycerol region of the lipid and near the choline group, when present. (2)H NMR of indole-d(7)-incorporated lipid bilayers reveals that the former site is occupied by about two-thirds of the indole, which adopts a distinct preferred orientation with respect to the bilayer normal. The results suggest that the upper hydrocarbon chain/glycerol location is dictated by many factors, including interactions with the electric charges and dipoles, van der Waals interactions, entropic contributions, and hydrogen bonding. Indole diffusion rates are higher in lipids with ester bonds and lower in choline-containing lipids, suggesting that interactions between indole and carbonyl groups are of minor importance for lipid-indole association and that cation-pi interactions with choline drive the second indole location. Nuclear Overhauser effect spectroscopy cross-relaxation rates suggest a 30-ns lifetime for indole-lipid associations. These results may have important implications for sidedness and structural transitions in tryptophan-rich membrane proteins.

Choline↗
PubMed2005

Molecular dynamics investigation of dynamical properties of phosphatidylethanolamine lipid bilayers.

We describe the dynamic behavior of a 1-stearoyl-2-oleoyl-phosphatidylethanolamine (SOPE) bilayer from a 20 ns molecular dynamics simulation. The dynamics of individual molecules are characterized in terms of (2)H spin-lattice relaxation rates, nuclear overhauser enhancement spectroscopy (NOESY) cross-relaxation rates, and lateral diffusion coefficients. Additionally, we describe the dynamics of hydrogen bonding through an analysis of hydrogen bond lifetimes and the time evolution of clusters of hydrogen bonded lipids. The simulated trajectory is shown to be consistent with experimental measures of internal, intermolecular, and diffusive motion. Consistent with our analysis of SOPE structure in the companion paper, we see hydrogen bonding dominating the dynamics of the interface region. Comparison of (2)H T(1) relaxation rates for chain methylene segments in phosphatidylcholine and phosphatidylethanolamine bilayers indicates that slower motion resulting from hydrogen bonding extends at least three carbons into the hydrophobic core. NOESY cross-relaxation rates compare well with experimental values, indicating the observed hydrogen bonding dynamics are realistic. Calculated lateral diffusion rates (4 +/ -1 x 10(-8) cm(2)s) are comparable, though somewhat lower than, those determined by pulsed field gradient NMR methods.

Algorithms↗
PubMed2005

Lipid-ethanol interaction studied by NMR on bicelles.

The interaction of ethanol with phospholipids was studied in bicelles at a physiologically relevant ethanol concentration of 20 mM and a lipid content of 14 wt % by high-resolution NMR. Transient association of ethanol with magnetically aligned bicelles imparts a small degree of anisotropy to the solute. This anisotropy allows detection of residual (1)H-(1)H and (1)H-(13)C dipolar couplings, which are superimposed on scalar couplings. Residual (2)H NMR quadrupole splittings of isotope-labeled ethanol were measured as well. The analysis of residual tensorial interactions yielded information on the orientation and motions of ethanol in the membrane-bound state. The fraction of phosphatidylcholine-bound ethanol was determined independently by gas chromatography and NMR. About 4% of ethanol is bound to phosphatidylcholine at a bicelle concentration of 14 wt % at 40 degrees C. Free and bound ethanol are in rapid exchange. The lifetime of ethanol association with phosphatidylcholine membranes is of the order of a few nanoseconds.

Chemistry, Physical↗
PubMed2005

Properties of docosahexaenoic-acid-containing lipids and their influence on the function of rhodopsin.

The importance of highly polyunsaturated fatty acids in health and development has been convincingly demonstrated by many studies over the past several decades. The mechanisms by which polyunsaturated lipid species might influence biological function at the molecular level are now attracting considerable attention. The G-protein-coupled receptor rhodopsin and docosahexaenoic acid, the dominant fatty acid in the retinal membrane, provide the best-studied example of protein function being influenced by lipid environment.

Animals↗
PubMed2005

Expression of human peripheral cannabinoid receptor for structural studies.

Human peripheral-type cannabinoid receptor (CB2) was expressed in Escherichia coli as a fusion with the maltose-binding protein, thioredoxin, and a deca-histidine tag. Functional activity and structural integrity of the receptor in bacterial protoplast membranes was confirmed by extensive binding studies with a variety of natural and synthetic cannabinoid ligands. E. coli membranes expressing CB2 also activated cognate G-proteins in an in vitro coupled assay. Detergent-solubilized receptor was purified to 80%-90% homogeneity by affinity chromatography followed by ion-exchange chromatography. By high-resolution NMR on the receptor in DPC micelles, it was determined that purified CB2 forms 1:1 complexes with the ligands CP-55,940 and anandamide. The receptor was successfully reconstituted into phosphatidylcholine bilayers and the membranes were deposited into a porous substrate as tubular lipid bilayers for structural studies by NMR and scattering techniques.

Escherichia coli↗
PubMed2004

Multinuclear NMR studies of single lipid bilayers supported in cylindrical aluminum oxide nanopores.

Lipid bilayers were deposited inside the 0.2 microm pores of anodic aluminum oxide (AAO) filters by extrusion of multilamellar liposomes and their properties studied by 2H, 31P, and 1H solid-state NMR. Only the first bilayer adhered strongly to the inner surface of the pores. Additional layers were washed out easily by a flow of water as demonstrated by 1H magic angle spinning NMR experiments with addition of Pr3+ ions to shift accessible lipid headgroup resonances. A 13 mm diameter Anopore filter of 60 microm thickness oriented approximately 2.5 x 10(-7) mol of lipid as a single bilayer, corresponding to a total membrane area of about 500 cm2. The 2H NMR spectra of chain deuterated POPC are consistent with adsorption of wavy, tubular bilayers to the inner pore surface. By NMR diffusion experiments, we determined the average length of those lipid tubules to be approximately 0.4 microm. There is evidence for a thick water layer between lipid tubules and the pore surface. The ends of tubules are well sealed against the pore such that Pr3+ ions cannot penetrate into the water underneath the bilayers. We successfully trapped poly(ethylene glycol) (PEG) with a molecular weight of 8000 in this water layer. From the quantity of trapped PEG, we calculated an average water layer thickness of 3 nm. Lipid order parameters and motional properties are unperturbed by the solid support, in agreement with existence of a water layer. Such unperturbed, solid supported membranes are ideal for incorporation of membrane-spanning proteins with large intra- and extracellular domains. The experiments suggest the promise of such porous filters as membrane support in biosensors.

Aluminum Oxide↗
PubMed2004

Multi-dimensional pulsed field gradient magic angle spinning NMR experiments on membranes.

The benefits of gradient techniques in the study of lipid membranes are demonstrated on a sample of 1-palmitoyl-2-oleoyl-sn-glycero-3 phosphocholine (POPC) liposomes embedded with ibuprofen. Most techniques from gradient NMR spectroscopy on solution samples are directly applicable to membrane samples subjected to magic angle spinning (MAS). Gradient-enhanced homo- and heteronuclear chemical shift correlation techniques were used to make resonance assignments. Gradient NOESY experiments provide insight into the location and dynamics of lipids, ibuprofen and water. Application of gradients not only reduces experiment time but also the t(1) noise in the multi-dimensional spectra. Diffusion measurements with pulsed field gradients characterize lateral movements of lipid and drug molecules in membranes. The theoretical framework for data analysis of MAS diffusion experiments on randomly oriented multilamellar liposomes is presented.

Calibration↗