Bacteriorhodopsin
| Bacteriorhodopsin | ||
|---|---|---|
|
||
| Biological structure, according to PDB 1M0K . | ||
| Mass / length primary structure | 249 amino acids | |
| Secondary to quaternary structure | Homotrimer; multipass membrane protein | |
| Identifier | ||
| Gene name (s) | bop | |
| External IDs | ||
| Transporter classification | ||
| TCDB | 3.E.1 | |
| designation | Ion-displacing microbial rhodopsin | |
| Occurrence | ||
| Homology family | Bacteriorhodopsin | |
| Parent taxon | Halobacteria | |
Bacteriorhodopsin (BR) is an integral membrane protein in the cell membrane of the extremophilic organism Halobacterium salinarum ( Halobacteria ). The BR protein is the light energy converter for the phototrophic energy production of Halobacterium salinarum . By salinarum Halobacterium accomplished prototrophy fundamentally different from Photosynthesen , for example by oxygenic photosynthesis of plants. The light energy is not used here to split water, but is used via the energy converter BR to build up a difference in proton concentration between the interior (cytoplasm) and the exterior of the bacterium. This difference in concentration is the source of energy for ATP synthase . Due to its extraordinary functionality, the protein is of great scientific interest, and a number of technical applications have been proposed for BR.
history
The name "Bacteriorhodopsin" for a protein of the purple membrane (purple membrane) of Halobacterium salinarum ( halobacteria ) was proposed in 1971 by the biochemist Dieter Oesterhelt and the electron microscope specialist Walther Stoeckenius . Together with the biophysicist Allen E. Blaurock, they had proven that the purple membrane of Halobacterium contains a crystalline retinal protein. Two years later, Oesterhelt and Stoeckenius characterized the function of the purple membrane as a light-dependent proton transport, and interpreted this as a simple form of photosynthesis. At the latest after Richard Henderson and Nigel Unwin had created a structural model of the protein using electron microscopy in 1975, bacteriorhodopsin advanced to become a model object of bioenergetics, membrane and structural biology. From the mid-1970s onwards, more than a hundred publications a year appeared on the subject, and related proteins such as halorhodopsin or sensorhodopsins were described. Plans for the technical use of the purple membrane containing the bacteriorhodopsin have been found since the late 1970s.
Structure of the protein
The protein of the BR consists of 248 amino acids which, arranged in seven approximately parallel alpha helices , cross the cell membrane and form a pore. A retinal molecule bound to the protein is located in this pore. Retinal is the chromophore of the molecule and is bound to the amine function of the amino acid Lys216 via an amide bond, usually referred to in this context as Schiff's base . Under physiological conditions the chromophore is only present as all-trans and 13-cis isomers. The isomerization takes place under the action of light.
BR forms two-dimensional crystalline areas in the cell membrane of Halobacterium salinarum , aggregated to trimers . These areas, up to five micrometers in size, in which BR trimers are present in a two-dimensional hexagonal arrangement in the lipid bilayer, are called the purple membrane (PM). The embedding of the BR in the purple membrane leads to a remarkable stability of the protein against physico-chemical influences. In this way, the color and photochemical activity of the PM are retained in the presence of oxygen and in a dry state.
Function of the protein
BR can be thought of as a light energy powered molecular machine that pumps protons . In a multi-step process, initiated by the light-induced isomerization of the chromophore and driven by changes in the proton affinities of amino acid functions, protons are shifted from the cytoplasmic to the extracellular side through the pore of the protein. The isomerization of the retinal chromophore as a result of light absorption is the trigger for the directed proton shift. In the unexposed state, the chromophore is a mixture of all- trans and 13- cis -retinal, after exposure it is only in the 13- cis configuration. Due to the embedding of the chromophore, this results in structural changes in the protein, which has a direct effect on the initially protonated state of the Schiff base . After the isomerization, this proton is in an energetically unfavorable environment and is given off to the direct interaction partner of the Schiff base, Asp85, in the extracellular direction. This is linked to a sequence of four further unidirectional proton shifts before the protein's initial state is finally restored and a new cycle can be run through. This light-driven pumping of protons is linked to a cyclic sequence of spectroscopically distinguishable states of the protein. This sequence is called the photocycle. The passage of the photocycle as a result of exposure is associated with a reversible color change from purple (B-state, absorption maximum 570 nm) to yellow (M-state, absorption maximum 410 nm).
Technical applications
Security printing pigment
Bacteriorhodopsin was first used as a photochromic pigment in security printing inks.
Protein storage with 50 terabytes of capacity
This enormous storage space is made possible by the light sensitivity of the BR protein. When light falls on the protein, it turns into a number of different molecules, each of which has a characteristic shape and color, before it returns to its original state. This intermediate stage is used to generate chemical energy and lasts about an hour in nature. By modifying the bacterium's DNA, this condition can be maintained for several years. Transferred to the binary system of computer technology, the basic state means a 0 and the changed state a 1.
literature
- Jean-Baptiste Waldner: Nano-informatique et intelligence ambiante . Hermes Science Publications, London 2006, ISBN 978-2-7462-1516-0
Individual evidence
- ^ Allen E. Blaurock, Walther Stoeckenius: Structure of the Purple Membrane . In: Nature New Biology . tape 233 , no. 39 , September 1971, p. 152-155 , doi : 10.1038 / newbio233152a0 .
- ↑ Dieter Oesterhelt, Walther Stoeckenius: Rhodopsin-like Protein from the Purple Membrane of Halobacterium halobium . In: Nature New Biology . tape 233 , no. 39 , September 1971, p. 149-152 , doi : 10.1038 / newbio233149a0 .
- ↑ W. Stoeckenius: From membrane structure to bacteriorhodopsin . In: The Journal of Membrane Biology . tape 139 , no. 3 , May 1994, pp. 139-148 , doi : 10.1007 / BF00232619 .
- ↑ Dieter Oesterhelt, Walther Stoeckenius: Functions of a New Photoreceptor Membrane . In: Proceedings of the National Academy of Sciences . tape 70 , no. October 10 , 1973, p. 2853-2857 ( pnas.org ).
- ^ R. Henderson, PNT Unwin: Three-dimensional model of purple membrane obtained by electron microscopy . In: Nature . tape 257 , no. 5521 , September 1975, pp. 28-32 , doi : 10.1038 / 257028a0 .
- ^ Mathias Grote, Maureen A. O'Malley: Enlightening the life sciences: the history of halobacterial and microbial rhodopsin research . In: FEMS Microbiology Reviews . tape 35 , no. 6 , November 2011, p. 1082-1099 , doi : 10.1111 / j.1574-6976.2011.00281.x .
- ↑ Heiko Patzelt, Bernd Simon, Antonius terLaak, Brigitte Kessler, Ronald Kühne, Peter Schmieder, Dieter Oesterhelt, Hartmut Oschkinat: The structures of the active center in dark-adapted bacteriorhodopsin by solution state NMR spectroscopy . In: Proceedings of the National Academy of Sciences . Vol. 99, No. 15, 2002, pp. 9765-9770, doi: 10.1073 / pnas.132253899 .
- ↑ Martin Neebe: Bacteriorhodopsin as a multifunctional photochromic color pigment for security technology . Dissertation Philipps-Universität Marburg 2003, DNB 968682308 .
- ↑ David J. Mehrl, Thomas F. Krile: Multiplexed Holographic Data Storage in Bacteriorhodopsin . June 1999 ( nasa.gov ).
Web links
- Prof. Dr. Norbert Hampp on the use of bacteriorhodopsin as a safety pigment (with experiments) (video on chymiatrie.de)