User:Maria.mendizabal/sandbox

Original- “Bacteriorhodopsin”

It is the retinal molecule that changes its conformation when absorbing a photon, resulting in a conformational change of the surrounding protein and the proton pumping action. It is covalently linked to Lys216 in the chromophore by Schiff base action. After photoisomerization of the retinal molecule, Asp85 becomes a proton acceptor of the donor proton from the retinal molecule. This releases a proton from a "holding site" into the extracellular side (EC) of the membrane. Reprotonation of the retinal molecule by Asp96 restores its original isomerized form. This results in a second proton being released to the EC side. Asp85 releases its proton into the "holding site," where a new cycle may begin.

Chemiosmotic coupling between the sun energy, bacteriorhodopsin and phosphorylation by ATP synthase(chemical energy) during photosynthesis in halophilic archaea Halobacterium salinarum (syn. H. halobium). The archaeal cell wall is omitted.

The bacteriorhodopsin molecule is purple and is most efficient at absorbing green light (wavelength 500-650 nm, with the absorption maximum at 568 nm). Bacteriorhodopsin has a broad excitation spectrum. For a detection wavelength between 700 and 800 nm, it has an appreciable detected emission for excitation wavelengths between 470 nm and 650 nm (with a peak at 570 nm). When pumped at 633 nm, the emission spectrum has appreciable intensity between 650 nm and 850 nm.

Bacteriorhodopsin belongs to the microbial rhodopsins. They have similarities to vertebrate rhodopsins, the pigments that sense light in the retina. Rhodopsins also contain retinal; however, the functions of rhodopsin and bacteriorhodopsin are different, and there is limited similarity in their amino acid sequences. Both rhodopsin and bacteriorhodopsin belong to the 7TM receptor family of proteins, but rhodopsin is a G protein-coupled receptor and bacteriorhodopsin is not. In the first use of electron crystallography to obtain an atomic-level protein structure, the structure of bacteriorhodopsin was resolved in 1990. It was then used as a template to build models of G protein-coupled receptors before crystallographic structures were also available for these proteins.

Many molecules have homology to bacteriorhodopsin, including the light-driven chloride pump halorhodopsin (for which the crystal structure is also known), and some directly light-activated channels like channelrhodopsin.

All other phototrophic systems in bacteria, algae, and plants use chlorophylls or bacteriochlorophylls rather than bacteriorhodopsin. These also produce a proton gradient, but in a quite different and more indirect way involving an electron transfer chain consisting of several other proteins. Furthermore, chlorophylls are aided in capturing light energy by other pigments known as "antennas"; these are not present in bacteriorhodopsin-based systems. It is possible that phototrophy independently evolved at least twice, once in bacteria and once in archaea.

Edit- “Bacteriorhodopsin”

It is the retinal molecule that changes its conformation when absorbing a photon, resulting in a conformational change of the surrounding protein and the proton pumping action. It is covalently linked to Lys216 in the chromophore by Schiff base action. After photoisomerization of the retinal molecule, Asp85 becomes a proton acceptor of the donor proton from the retinal molecule. This releases a proton from a "holding site" into the extracellular side (EC) of the membrane. Reprotonation of the retinal molecule by Asp96 restores its original isomerized form. This results in a second proton being released to the EC side. Asp85 releases its proton into the "holding site," where a new cycle may begin.

Chemiosmotic coupling between the sun energy, bacteriorhodopsin and phosphorylation by ATP synthase(chemical energy) during photosynthesis in halophilic archaea Halobacterium salinarum (syn. H. halobium). The archaeal cell wall is omitted.

The bacteriorhodopsin molecule is purple and is most efficient at absorbing green light (wavelength 500-650 nm, with the absorption maximum at 568 nm). Bacteriorhodopsin has a broad excitation spectrum. For a detection wavelength between 700 and 800 nm, it has an appreciable detected emission for excitation wavelengths between 470 nm and 650 nm (with a peak at 570 nm). When pumped at 633 nm, the emission spectrum has appreciable intensity between 650 nm and 850 nm.

Bacteriorhodopsin belongs to the microbial rhodopsins. They have similarities to vertebrate rhodopsins, the pigments that sense light in the retina. Rhodopsins also contain retinal; however, the functions of rhodopsin and bacteriorhodopsin are different, and there is limited similarity in their amino acid sequences. Both rhodopsin and bacteriorhodopsin belong to the 7TM receptor family of proteins, but rhodopsin is a G protein-coupled receptor and bacteriorhodopsin is not. In the first use of electron crystallography to obtain an atomic-level protein structure, the structure of bacteriorhodopsin was resolved in 1990. It was then used as a template to build models of G protein-coupled receptors before crystallographic structures were also available for these proteins.

Many molecules have homology to bacteriorhodopsin, including the light-driven chloride pump halorhodopsin (for which the crystal structure is also known), and some directly light-activated channels like channelrhodopsin.

All other phototrophic systems in bacteria, algae, and plants use chlorophylls or bacteriochlorophylls rather than bacteriorhodopsin. These also produce a proton gradient, but in a quite different and more indirect way involving an electron transfer chain consisting of several other proteins. Furthermore, chlorophylls are aided in capturing light energy by other pigments known as "antennas"; these are not present in bacteriorhodopsin-based systems. It is possible that phototrophy independently evolved at least twice, once in bacteria and once in archaea.

Rhodopsins are a subject of ongoing research due to their many practical applications. They serve as a research tool since bacteriorhodopsins can harness the energy of light to move different cations and anions. Halorhodopsins, for example move chloride ions, as well as other halides. By using a similar approach with anions, this could allow for significantly reducing metabolic energy by achieving osmotic balance in a cell. Ongoing research is being devoted seeking for more homologs of the molecule. It is also the reason why rhodopsins are one of the first membrane molecules whose entire crystal structure was characterized by crystallography. Halorhodopsin is currently being used in optogenetics to hyperpolarize specific neurons.

Citations:

Gradinaru, V., Thompson, K. R., & Deisseroth, K. (2008). eNpHR: a Natronomonas halorhodopsin enhanced for optogenetic applications. Brain Cell Biology, 36(1-4), 129–139. http://doi.org/10.1007/s11068-008-9027-6

NIH. (2005). Halorhodopsins. Retrieved September 25, 2017 from: https://meshb.nlm.nih.gov/record/ui?name=Halorhodopsin

OPM. (2013). Bacteriorhodopsin Orientation in membrane. Retrieved September 25, 2017 from: https://meshb.nlm.nih.gov/record/ui?name=Halorhodopsinhttp://opm.phar.umich.edu/contact.php

Maria.mendizabal (talk) 05:51, 26 September 2017 (UTC)

Maria.mendizabal (talk) 19:39, 8 October 2017 (UTC)