Which bacteria contain bR?

Structural Properties

Functional Properties

Technological Importance

Which bacteria contain bR? (TOP)

Bacteriorhodopsin (bR) was discovered in membrane of Halobacterium salinarium by Stoeckenius and Oesterheltin in 1973. Halobacterium salinarium is extremely halophilic archaebacterium. This species of bacteria can live in the habitats that have high salt concentration, such as natural salt marshes and salterns, where salt is produced from saltwater by evaporation. The main reason of the red colour in these places is the red carotenoid pigments of Halobacterium. The optimal salt concentration for this bacterium is between 20-25%. This level of the salt concentration is 6-7 times higher than the seawater.  

Tuz Lake (Turkey)

Structural Properties (TOP)

The structure of bR was first determined in 1975 by Richard Henderson and Nigel Unwin using electron micrographs (7 Å) of the purple membrane. Clarification studies of the molecular structure of the bR via cryo-EM (3,4 Å) were carried out by Henderson et al in 1990. More detailed information about the structure of bR in 1.5 Å resolution scale was obtained by novel research activities of several laboratories in 1999.

Bacteriorhodopsin is a 26 kDa weighed integral membrane protein which pumps protons across the membrane by using sunlight. 3D structure of the bR is formed by the arrangement of 248 amino acids in seven transmembrane helical segments.A all-trans retinal chromophore of bR is enclosed within these helical segments.This retinal chromophore is a derivative of the ß- carotene, and it is bound via protonated Schiff base to ε-amino group of Lysine-216 near the center of helices and lies nearly parallel to the plain of membrane. It is found in the cell membrane with a higher concentration ratio with respect to the other membrane proteins. Due to high concentration of bR, the bacterial membrane has a purple–patched appearance.  

Hexagonal structure of Purple Membrane

Functional Properties (TOP)

bR pumps the proton from the inside of the cell to the outside by using the energy it received from sunlight, and as a result,  a proton gradient occurs across the membrane. With the enforcement of this generated proton gradient, protons are driven to inside of the cell through the ATP-synthase, in order to balance proton concentrations between these two environments. In this step, The ATP-synthase provides the production of the ATP using protons, therefore, the energy that the cell required for would be produced.

bR follows a cyclic pathway during proton pumping. bR shows some conformational alterations along with the sunlight. There are some determined transition circumstances of the protein in these alterations, these circumstances are called intermediate, and the intermediates shows the maximum absorption values that are used for nomenclature of the intermediates like this respectively; bR₅₆₈, K₅₉₀, L₅₅₀, M₄₁₂, N₅₅₀, O₆₄₀.

Technological Importance (TOP)

Bacteriorhodopsin (BR) is the key protein for the halobacterial photosynthetic capabilities and is one of the very rare molecules which occur in crystalline form in nature. Since its discovery, which was reported in 1971, many efforts have been made to exploit the obvious technical potential of this molecule. Successful application of gene technology methods for the modification of the physical function of a biomolecule was first demonstrated with BR. This approach points the way to a new class of materials derived from evolutionary optimized biomaterials by genetic re-engineering. Mutated BRs proved to have significant advantages over the wild type in optical applications. The current status of potential technical applications of BR is reviewed. BR is employed as a photoelectric, photochromic or energy- converting element. First systems now exist which demonstrate the successful integration of this new material into existing technologies. Analyzing the patents filed, which claim the processing or application of BR, gives an indication to areas where further technical uses are to be expected in the near future. (N.A.Hampp Appl. Microbiol. Biotechnol. (2000) 53: 633-639.)

3D Memory of bR designed by Birge Group

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