Light-driven proton-pump membrane protein

ITowever, membrane proteins can also be distributed in nonrandom ways across the surface of a membrane. This can occur for several reasons. Some proteins must interact intimately with certain other proteins, forming multisubunit complexes that perform specific functions in the membrane. A few integral membrane proteins are known to self-associate in the membrane, forming large multimeric clusters. Bacteriorhodopsin, a light-driven proton pump protein, forms such clusters, known as purple patches, in the membranes of Halobacterium halobium (Eigure 9.9). The bacteriorhodopsin protein in these purple patches forms highly ordered, two-dimensional crystals. 

BR from H. salinarum is a light-driven proton pump, which is triggered by the photoisomerization of retinal covalently linked to its Lys216. It consists of a single polypeptide of 248 amino-acid residues, including seven a-helical TM chains A-G and interconnecting loops, as schematically illustrated in Figure 23. BR is one of the most intensively studied membrane proteins. A variety of experimental techniques have shown it to be... 

The CP MAS NMR spectroscopy has been also extensively used for studies of proteins containing retinylidene chromophore like proteorhodopsin or bacteriorhodopsin. Bacteriorhodopsin is a protein component of purple membrane of Halobacterium salinarium.71 7 This protein contains 248 amino acids residues, forming a 7-helix bundle and a retinal chromophore covalently bound to Lys-216 via a Schiff base linkage. It is a light-driven proton pump that translocates protons from the inside to the outside of the cell. After photoisomerization of retinal, the reaction cycle is described by several intermediate states (J, K, L, M, N, O). Between L and M intermediate states, a proton transfer takes place from the protonated Schiff base to the anionic Asp85 at the central part of the protein. In the M and/or N intermediate states, the global conformational changes of the protein backbone take place. 

The incorporation of a membrane protein into a polymerizable liposome from (22) was demonstrated by R. Pabst n9). The chromoprotein bacteriorhodopsin — a light-driven proton pump from halophilic bacteria — was incorporated into monomeric sulfolipid liposomes by ultrasonication. The resulting proteoliposomes were poly-... 

A three-dimensional structure also has been elucidated for bacteriorhodopsin, an integral membrane protein of the halophilic (salt-loving) bacterium Halobacterium halobium. This protein has been studied intensively because of its remarkable activity as a light-driven proton pump (see chapter 14). It forms well-ordered arrays in two-dimensional sheets that can be studied by electron diffraction. Measurements of the diffraction patterns show clearly that bacteriorhodopsin has seven transmembrane helices (fig. 17.12). 

Many of the early genetic studies were done on H. halobium and its related strains. The popularity of these strains stemmed from the fact that several interesting spontaneous mutations could be readily detected. Among the most characterized mutations are those that affect the production of the protein part of the purple membrane, the heavily studied light-driven proton pump bacteriorhodopsin. Spontaneous mutations occur at a frequency of lO 4. Analysis of these mutations showed that in almost every case a foreign DNA sequence was introduced into the bacterioopsin (bop) structural gene or into sequences surrounding it. 

Light is indispensable for life. Green plants and some bacteria use solar energy for the energy source in their photosynthesis [1-3]. Archeal bacteriorhodopsin is a membrane bound protein and works as a light-driven proton pump [4, 5]. Another role of light is information carrier that is recognized in vision and photo-sensors. 

Bacteriorhodopsin, a light-driven proton pump, is a large (27000 Dalton) membrane protein, located in the purple membrane of halobacterium halobium (for a recent review see Lanyi, 1993). It spans the membrane by seven-a-helices (see Fig 6.6-7). The chro-mophore retinal is embedded inside the protein, shielded by the helices. Retinal connects to the Lys 216 of the protein via a protonated Schiff s base (Fig. 6.6-7). 

Bacteriorhodopsin is the sole membrane protein of seven a-helical transmembrane chains present in the purple membrane of Halobacterium salinarum. This is active as a light-driven proton pump through the photoisomerization of retinal (Fig. 2) from the aW-trans, 15-anti to the 13-cis, 15-anti form covalently linked to Lys216 (helix G) of a single-chain polypeptide of 248 amino acid... 

We summarise recent work on computer modelling and simulation of proteins involved in bioenergetic processes and in peptide-membrane interactions. Homology modelling, electrostatic calculations and conformational analysis of a photosynthetic reaction centre protein are described. Bacteriorhodopsin, a light-driven proton pump protein is examined from several aspects, including its hydration and conformational thermodynamics. Finally, we present results on lipid perturbation on interaction with a cyclic decapeptide antibiotic, gramicidin S. 

Very recently first SERRS results about bacteriorhodopsin have been communicated by Nabiev et al. Bacteriorhodopsin is a membrane protein found in bacteria which functions as a light driven proton pump. Using the short-range mechanism of SERS (Chapt. 4.1) the active site (retinal chromophore) position of the protein in the membrane has been estimated with high accuracy It is interesting to note, that adsorption of bacteriorhodopsin on silver colloids seems to fix light-induced cyclic transformations in the protein active sites. 

The photocycle of bacteriorhodopsin, the protein pigment of the purple membrane of Halobacterium halobium has generated considerable interest in the field of molecular photobiology, (see Ref. 2-4 for recent views). This is due to the close relationship between its photocycle and the mechanism of the light-driven proton pump ) which is capable of driving ATP synthesisand also to the striking structural and photophysical analogies between bacteriorhodopsin... 

The purple membrane (PM) exists in the plasma membrane of Halobacterium halobium, and its constituent protein, bacteriorhodopsin (bR), functions as a light-driven proton pump. In the PM, bR monomers are associated to form a trimeric oligomer and the trimers are arranged in a hexagonal lattice (see also chapters 17 and 18). However, several aspects in the crystal formation remain open for example, (1) trimer-trimer interaction sites and association energy and (2) existence of preformed trimers in the fluidic noncrystal region. In the 2D crystal of bR and any crystals in general, they are in dynamic equilibrium with the constituents at the interface between the crystal and the liquid phase. Here, we visualized dynamic events at the interface in the PM to provide information of the crystal formation and intermolecular interactions. ... 

---