China 
Africa 
Explore chapters and articles related to this topic
Receptors and Signal Transduction Pathways Involved in Autonomic Responses
Published in Kenneth J. Broadley, Autonomic Pharmacology, 2017
The amino acid sequences of the G protein-linked receptors have been determined and shown to consist of single polypeptide chains. None of the receptors have been crystallized, so that the three-dimensional geometry of the receptors is not yet known. Bacteriorhodopsin is the purple-membrane protein of Halobacterium halobium, a halophilic (salt-loving) bacterium, which contains a retinal chromophore similar to rhodopsin, the visual pigment of mammalian eyes. This 25 kDa protein has a photosynthetic function in the absence of oxygen, to pump protons (H+) from inside the bacterial cell to the outside, when it is exposed to light. As a result, ADP is converted to ATP. Bacteriorhodopsin is a membrane-spanning protein not coupled to a G protein, but probably making up the ion channel of the proton pump. It has been crystallized, making X-ray crystallography possible for elucidating the three-dimensional structure. High-resolution electron microscopy has shown this protein to consist of seven closely packed hydrophobic membrane-spanning α-helices extending nearly perpendicular to the plane of the membrane, some of the α-helices probably being tilted. Subsequently, the sequence of the visual pigment, bovine rhodopsin, was determined and its predicted structure was similar to that identified for bacteriorhodopsin. This model has served as the basis for the structural arrangement of all G protein-coupled receptors.
General and Practical Aspects of Membrane Protein Crystallization
Published in Hartmut Michel, Crystallization of Membrane Proteins, 1991
With most other membrane protein crystals the situation is different. In the case of bacteriorhodopsin, the reaction center from Rb. sphaeroides, several light-harvesting complexes from photosynthetic bacteria, and porin from E. coli with the same precipitating agent and under the same conditions of ionic strength, pH, and temperature, the same crystal form is obtained when a slightly different detergent is used. These observations probably indicate that protein-protein interactions are the dominant driving forces for the crystallization of these proteins.
FT-IR Studies of Molecular Conformation in Biological Membranes
Published in R. Michael Gendreau, Spectroscopy in the Biomedical Sciences, 1986
David G. Cameron, Richard A. Dluhy
In addition to the rhodopsin molecule in vertebrates, another photosensitive membrane has been the object of much biophysical interest. It is the purple membrane from Halobacterium halobium which contains the protein bacteriorhodopsin. This bacterial pigment also contains the retinal chromophore covalently linked via a protonated Schiff base to its protein matrix. However, unlike rhodopsin, the conversion of light to chemical energy in bacteriorhodopsin serves to generate a proton gradient across the cell membrane by acting as a proton pump.
Advances with weak affinity chromatography for fragment screening
Published in Expert Opinion on Drug Discovery, 2019
Fotios Tsopelas, Anna Tsantili-Kakoulidou
The sterically stabilized bilayer disks, termed lipodisks, have been suggested as an interesting alternative to liposomes. Polypispersity is avoided, while their surfaces are more accessible to the surroundings. For stabilization polyethylene glycol (PEG) is used, since it was found that Polyethylene glycol (PEG) substituted lipids often used at low amount in liposomes begin to form bilayer disks upon increase of their concentration [68]. Lipodisks have a planar and circular shape, where the PEG lipids are located at the rim of the disks, offering steric protection against fusion and self-closure. It has been shown that they function well as model membranes in drug partition studies [69–71], while they can be immobilized on Superdex gel beads material to be used as columns in ILC [70]. Further investigations using bacteriorhodopsin suggest that bilayer disks are suitable matrix for reconstitution of membrane proteins [70]. The gradual progress from liposomes to lipodisks and to ‘proteolipodisks’ integrated in ILC, created the circumstances which enabled further advancement of WAC Chromatography to include membrane proteins as targets for fragment ligand interactions. The protein immobilized with lipodisks onto a silica surface can achieve two possible positions, as shown in Figure 3. The ideal situation is indirect attachment via the primary amine of the lipodisk (i.e., solely via the lipodisks). Or the protein is coupled directly to the silica via amine moieties present in the protein [53,54].
An outlook on using serial femtosecond crystallography in drug discovery
Published in Expert Opinion on Drug Discovery, 2019
Alexey Mishin, Anastasiia Gusach, Aleksandra Luginina, Egor Marin, Valentin Borshchevskiy, Vadim Cherezov
An entirely different type of injectors based on the electrospinning principle was designed to substantially reduce the crystal flow rate and thus sample consumption. The first version, called a microfluidic electrokinetic sample holder (MESH) [41], could achieve flow rates down to 0.14 µl/min but required the addition of a cryoprotectant, which was remedied by an optimized construction of a concentric-flow microfluidic electrokinetic sample holder (coMESH) [42]. Another very important injector, known as a lipidic cubic phase (LCP) or viscous media injector [43], offers a wide range of flow rates down to 1 nl/min and compatibility with crystallization of membrane proteins in a membrane-like environment of LCP [44]. An LCP injector was used to obtain about a dozen GPCR structures using less than 0.3 mg of crystallized protein per structure [45] and to record molecular movies of light-induced conformational changes in bacteriorhodopsin [46]. Apart from membrane proteins crystallized in LCP, an LCP injector can be used to efficiently deliver crystals of soluble proteins upon mixing them with a viscous carrier matrix, such as LCP, agarose, grease, etc. [47].
Collective excitations in α-helical protein structures interacting with the water environment
Published in Electromagnetic Biology and Medicine, 2020
Vasiliy N. Kadantsev, Alexey Goltsov
Then, we considered solutions of Equation (39) at weak damping, i.e., when 2013; Xie et al. 2002). Another mechanism of slow relaxation of the collective modes was suggested to be based on the experimental observation of vibrational wave pockets of a long lifetime over 500 picoseconds in bacteriorhodopsin exposed by picosecond far IR sources (Xie et al. 2002). The authors discussed a possible mechanism of slow relaxation due to quantum effects of restricted interaction of the low-frequency collective modes with solvent and suggested a link between undamped collective vibration and the conformational transitions in proteins enriched by α-helical structures.