Bacteriorhodopsins Halobacterium salinarum

Indeed, hydrophilic N- or C-terminal ends and loop domains of these membrane proteins exposed to aqueous phases are able to undergo rapid or intermediate motional fluctuations, respectively, as shown in the 3D pictures of transmembrane (TM) moieties of bacteriorhodopsin (bR) as a typical membrane protein in the purple membrane (PM) of Halobacterium salinarum.176 178 Structural information about protein surfaces, including the interhelical loops and N- and C-terminal ends, is completely missing from X-ray data. It is also conceivable that such pictures should be further modified, when membrane proteins in biologically active states are not always present as oligomers such as dimer or trimer as in 2D or 3D crystals but as monomers in lipid bilayers. 

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... 

Bacteriorhodopsin is a light-driven ion pump that is found in the purple membrane of the archaebacterium Halobacterium salinarum. Bacteriorhodopsin monomers consist of a bundle of seven transmembrane a-helices that are connected by short interhelical loops and enclose a molecule of retinal that is buried in the protein interior, approximately half way... 

Peck RF, Johnson EA, Krebs MP (2002) Identification of a lycopene P-cyclase required for bacteriorhodopsin biogenesis in the archaeon Halobacterium salinarum. J Bacteriol 184 2889-2897... 

In further membrane studies, the surface of Halobacterium salinarum was investigated in order to visualize the distribution of retinal-free and retinal-containing membrane domains (see Figure 11.12) [108]. Therein, the resonantly enhanced retinal moiety was used as a marker for the light-driven, proton-pump bacteriorhodopsin. In the first step, isolated purple membrane (PM) patches were characterized. In experiments on isolated PM patches, the sites of the retinal... 

In the 1970s and early 1980s, four rhodopsins were discovered in the cytoplasmic membrane of the archaeon Halobacterium salinarum the light-driven ion pumps bacteriorhodopsin (BR ) and halor-hodopsin and the phototaxis receptors sensory rhodopsin 1 (SRP), and sensory rhodopsin 11... 

FIGURE 124.2 Primary sequence comparison of the microbial rhodopsins. (Hs Halobacterium salinarum, Np Natronomonas pharaonis, BR bacteriorhodopsin, SR sensory rhodopsin, PR proteorhodopsin, NR Neurospora rhodopsin, CSRA and CSRB Chlamydomonas sensory rhodopsins A and B) Conserved residues are marked with black boxes, and residues in the retinal-binding pocket are marked with an asterisk. 

Bacteriorhodopsin is the predominant protein found in the purple membrane of Halobacterium salinarum (also historically referred to as Halobacterium halobium or Halobacterium salinarium), a halophilic (e.g., salt-loving ) organism that functions in environments where native salt concentrations exceed 4 molar, or approximately six times that of seawater. Introduced in this section are the phylogeny of the organism as well as the native environment of the organism. 

FIGURE 135.2 Magnification of Halobacterium salinarum from the native organism to the protein. (A) A rodshaped cluster of H. salinarum. (B) A single cell of H. salinarum. (C) A top view and side view of the two-dimensional crystalline lattice from the cell membrane of H. salinarum. Bacteriorhodopsin forms a trimer within this lipid lattice. 

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