Proteorhodopsin

Abstract

The membrane‐bound protein Proteorhodopsin (PR) is a simple light‐dependent proton pump. The single gene that encodes PR was detected in 2000 on genomic fragments of heterotrophic marine bacteria. Over the following years, researchers realised that the majority of bacteria in the photic zone (where light is present) of nearly all oceanic water bodies possess this protein. The high abundance of closely related PR genes in only distantly related bacteria is very likely due to frequent lateral gene transfer. Experiments with PR‐containing pure cultures did not show uniform results on improved growth upon illumination, indicating a functional diversity that probably depends on environmental nutrient conditions. In most cases, PR will help bacteria to produce additional energy without the need of oxidising organic carbon. This energy can be used to grow better, move faster or survive longer during starvation periods.

Key Concepts:

  • Most marine bacteria in surface waters contain proteorhodopsin, a protein that is closely related to other rhodopsins of Archaea and Eukarya.

  • Proteorhodopsin is a light‐dependent proton pump.

  • The huge phylogenetic diversity of PRs in the environment might reflect to some degree a functional diversity as well.

  • Environmental conditions have an impact on the function of PR for the residing bacteria.

  • The activity of PR can result in enhanced growth, faster movement or extended starvation survival.

  • The simplicity of the PR photosystem makes it an interesting target for biotechnological exploitation.

Keywords: proteorhodopsin; rhodopsin; bacteriorhodopsin; retinal; photoheterotroph; proton pump

Figure 1.

Schematic phylogenetic tree illustrating the relatedness of Proteorhodopsin to other opsins found in Archaea and Eukarya. Based on figures from Mongodin et al. and McCarren and DeLong .

Figure 2.

Red pigmented E. coli cells containing heterologously expressed proteorhodopsin.

Figure 3.

From the discovery of a gene in a marine water sample to an advanced hypothesis on its function and importance for the environment: A timeline and landmark papers of ten years of research on Proteorhodopsin.

Figure 4.

Simplified mode of action of Proteorhodopsin: Light energy is used to pump protons over the cytoplasmic membrane and create a proton motive force. This proton motive force will produce additional ATP that can be used for a variety of energy‐requiring processes.

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Further Reading

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Walter JM, Greenfield D and Liphardt J (2010) Potential of light‐harvesting proton pumps for bioenergy applications. Current Opinion in Biotechnology 21(3): 265–270.

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How to Cite close
Miyake, Sou, and Stingl, Ulrich(Mar 2011) Proteorhodopsin. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0022837]