Everything about Proteorhodopsin totally explained
Proteorhodopsin is a photoactive
retinylidene protein in marine bacterioplanktons. Just like the
homologous pigment
bacteriorhodopsin found in some
archaea, it consists of a transmembrane
protein bound to a
retinal molecule and functions as a light-driven
proton pump. Some members of the family (of more than 800 types) are believed to have sensory functions. Members are known to have different absorption spectra.
Proteorhodopsin was first discovered in
2000. It was found in the genomes of several species of uncultivated marine γ-
proteobacteria present in the Eastern
Pacific Ocean, Central North Pacific Ocean and
Southern Ocean,
Antarctica . Subsequently, genes of proteorhodopsin variants have been identified in samples from the
Mediterranean and
Red Seas and the
Sargasso Sea and the
Sea of Japan. These variants are not spread randomly, but have different distributions of absorption maxima along depth gradients and across locations .
On comparison to its better-known archaeal homolog bacteriorhodopsin, most of the active site residues of known importance to the bacteriorhodopsin mechanism are conserved in proteorhodopsin. Homologues of the
active site residues
Arg82, Asp85 (the primary
proton acceptor),
Asp212 and
Lys216 (the
retinal
Schiff base binding site) in bacteriorhodopsin are conserved as Arg94, Asp97, Asp227 and Lys231 in proteorhodopsin. However, in proteorhodopsin, there are no
carboxylic acid residues directly homologous to
Glu194 or Glu204 of bacteriorhodopsin, which are thought to be involved in the proton release pathway at the extracellular surface.
It seems likely that proteorhodopsin functions throughout the Earth's oceans as a light-driven H+ pump, by a mechanism similar to that of bacteriorhodopsin. As in bacteriorhodopsin, the retinal
chromophore of bacteriorhodopsin is covalently bound to the
apoprotein via a protonated
Schiff base at Lys231. The configuration of the retinal chromophore in
unphotolyzed proteorhodopsin is predominantly all-trans, and changes to 13-cis upon illumination with light. Several models of the complete proteorhodopsin photocycle have been proposed, based on
FTIR and UV–visible
spectroscopy; they resemble established photocycle models for bacteriorhodopsin
.
Genetic Engineering with Proteorhodopsins
If the gene for proteorhodopsin is inserted into
E. coli and retinal is given to these modified
bacteria, then that'll incorporate the
pigment into their
cell membrane and will pump protons in the presence of light.
Further Information
Get more info on 'Proteorhodopsin'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://proteorhodopsin.totallyexplained.com">Proteorhodopsin Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
