We express CB2 recombinantly in Escherichia coli as a fusion with maltose-binding protein and several affinity tags. The CB2-fusion protein is solubilized, purified, the fusion cleaved, and CB2 purified again from cleavage products. We extensively studied the effects of detergents, lipids and cannabinoid ligands on stability of the recombinant cannabinoid receptor CB2. The effort resulted in guidelines for preparation and handling of the fully functional receptor suitable for a wide array of downstream applications. We demonstrate that a concerted action of an anionic cholesterol derivative, cholesteryl hemisuccinate (CHS) and high affinity cannabinoid ligands CP-55,940 or SR-144,528 are required for efficient stabilization of the functional fold of CB2 in dodecyl maltoside (DDM)/ CHAPS detergent solutions. Similar to CHS, the negatively charged phospholipids with the serine headgroup (PS) exerted significant stabilizing effects in micelles while uncharged phospholipids were not effective. The purified CB2 reconstituted into lipid bilayers retained functionality for up to several weeks enabling high resolution structural studies of this GPCR at physiologically relevant conditions. Reconstitution of functional CB2 at the level of milligrams, and concentration to a volume of 40 microliters, sufficient for structural studies by solid state NMR has been achieved. Functionality of the receptor was verified by ligand binding using radioactive ligands as well as deuterated ligands in combination with 2H-MAS NMR and by G protein activation studies using recombinantly produced G protein in a GTPgammaS radioactive assay. Composition, size, and homogeneity of proteoliposomes were investigated by analytical NMR, fluorescence spectroscopy using labeled lipid and CB2, dynamic light scattering, and sucrose gradient centrifugation. Exploratory NMR experiments conducted on a 2-mg sample of homogeneously 13C- and 15N labeled CB2 and comparison of experimental results with simulated spectra obtained from the atomic coordinates of a CB2 model have demonstrated feasibility of the experimental concept. Specific isotopic labeling schemes are under development to achieve the desired spectral resolution for structural analysis. Structural and functional studies on CB2 may benefit from immobilization of the purified and functional receptor onto a suitable surface at a controlled density and, preferably in a uniform orientation. We develop strategies for preparation of functional recombinant CB2 and immobilization at solid interfaces. The successful deposition of CB2 was demonstrated by surface plasmon resonance. Membranes with a high content of polyunsaturated phosphatidylethanolamines (PE) facilitate formation of metarhodopsin-II (MII), the photointermediate of bovine rhodopsin that activates the G protein transducin. We determined whether MII-formation is quantitatively linked to the elastic properties of PEs. Curvature elasticity of monolayers of the polyunsaturated lipids 18:0-22:6n-3PE, 18:0-22:5n-6PE and the model lipid 18:1n-9-18:1n-9PE were investigated in the inverse hexagonal phase. All three lipids form lipid monolayers with rather low spontaneous radii of curvature of 26-28 Angstrom. Negative curvature elastic stress in membranes containing high concentrations of polyunsaturated PEs is very high. Release of even a small fraction of this stress from the layer of lipids surrounding the receptor is sufficient to shift the MI/MII equilibrium towards MII, the state that activates G protein. Furthermore, polyunsaturated bilayers have a hydrophobic thickness of about 27 A which has been determined to match the length of the hydrophobic transmembrane helices of rhodopsin. The data show that polyunsaturated lipids are important for class A GPCR activation, and we speculate that the rhodopsin model is particularly relevant for constitutive activity of GPCR and activation by weak agonists. In collaboration with MPBS, NINDS we contribute to investigation of the voltage-gated potassium channel KvAP by conducting solid-state NMR experiments. Our experiments with the S1-S4 voltage sensing domain of the channel suggest that lipids have weak and transient interactions with the protein that do not detectably alter the structure of the domain. Data obtained on S1-S4 domain embedded in lipid membranes are remarkably consistent with both X-ray and solution NMR structures of the domain obtained in detergent micelles. The S1S4 domain exhibits extensive interactions with lipids and the domain is heavily hydrated when embedded in a membrane. There is evidence for some preferential interactions of anionic lipids with the S1S4 domain. The arginine residues within the S1S4 domain, which play a major role in voltage sensing, are well hydrated and are positioned in close proximity to lipids, exhibiting close interactions with both lipid headgroups and acyl chains. We continue our studies on biophysical properties of the lipid matrix that are important for function of integral membrane proteins. In collaboration with laboratories that conduct molecular simulations, we explored the internal structure of the liquid ordered phase that forms in the presence of high cholesterol concentrations in membranes. The liquid ordered phase of a mixture of cholesterol and two lipids was shown to be itself inhomogeneous. Lateral segregation within the phase is observed, with regions of hexagonally packed saturated chains separated by interstitial regions enriched in cholesterol and unsaturated chains. The observed substructure explains existing experimental data and provides a focus for future efforts aimed at understanding the molecular scale structure of cell membranes. This picture of the phase provides an explanation for a number of experimental results, most of them obtained by NMR, which have until now lacked a consistent description in terms of a molecular model.
| Mhurchú, Niamh Ní; Zoubak, Lioudmila; McGauran, Gavin et al. (2018) Simplifying G Protein-Coupled Receptor Isolation with a Calcium-Dependent Fragment Complementation Affinity System. Biochemistry 57:4383-4390 |
| Jiang, Zhiping; Flynn, Jessica D; Teague Jr, Walter E et al. (2018) Stimulation of ?-synuclein amyloid formation by phosphatidylglycerol micellar tubules. Biochim Biophys Acta Biomembr : |
| Yeliseev, Alexei; Gawrisch, Klaus (2017) Expression and NMR Structural Studies of Isotopically Labeled Cannabinoid Receptor Type II. Methods Enzymol 593:387-403 |
| Blasic, Joseph R; Worcester, David L; Gawrisch, Klaus et al. (2015) Pore hydration states of KcsA potassium channels in membranes. J Biol Chem 290:26765-75 |
| Soubias, Olivier; Teague Jr, Walter E; Hines, Kirk G et al. (2015) Rhodopsin/lipid hydrophobic matching-rhodopsin oligomerization and function. Biophys J 108:1125-32 |
| Sodt, Alexander J; Sandar, Michael Logan; Gawrisch, Klaus et al. (2014) The molecular structure of the liquid-ordered phase of lipid bilayers. J Am Chem Soc 136:725-32 |
| Mihailescu, Mihaela; Krepkiy, Dmitriy; Milescu, Mirela et al. (2014) Structural interactions of a voltage sensor toxin with lipid membranes. Proc Natl Acad Sci U S A 111:E5463-70 |
| Kimura, Tomohiro; Vukoti, Krishna; Lynch, Diane L et al. (2014) Global fold of human cannabinoid type 2 receptor probed by solid-state 13C-, 15N-MAS NMR and molecular dynamics simulations. Proteins 82:452-65 |
| Locatelli-Hoops, Silvia C; Yeliseev, Alexei A (2014) Use of tandem affinity chromatography for purification of cannabinoid receptor CB?. Methods Mol Biol 1177:107-20 |
| Soubias, Olivier; Teague, Walter E; Hines, Kirk G et al. (2014) The role of membrane curvature elastic stress for function of rhodopsin-like G protein-coupled receptors. Biochimie 107 Pt A:28-32 |
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