• Bacteriorhodopsin

    measured on the SURFE2R N1

Bacteriorhodopsin

Target Synonyms and Classification: Bacteriorhodopsin (BR) belongs to the Ion-translocating Microbial Rhodopsin Family (MRF, TCDB: 3.E.1), which catalyzes light-driven ion translocation across microbial cytoplasmic membranes or serve as light receptors.

Function: BR provides a major source of energy: Using light energy it pumps protons across the membrane out of the cell and generates a proton gradient, which in turn is used to generate chemical energy in form of ATP through the action of the ATP-Synthase. Upon light absorption (λmax = 570 nm), the covalently bound cofactor Retinal undergoes a series of conformational transitions, which are coupled to the translocation of one proton. Proton translocation involves binding, intramolecular transfer, and release of a proton which requires – besides retinal – different amino acids. The whole photocycle takes about 15 ms.

Organism and Localization: Bacteriorhodopsin is used by Archaea, most notably by Haloarchaea like Halobacterium salinarum, an extremophile that occupies hypersaline lakes. BR forms two-dimensional crystalline patches known as the purple membrane, which can occupy up to 50 % of the surface area of the archaeal cell.

Substrates and Inhibitors: Proton translocation by BR is inhibited by blue light, which is known as the “blue light effect”. Blue light enables a shortcut within the photocycle which leads to uncoupling of light adsorption from H+ translocation. BR can be inactivated by mutation of the proton donor D96 to asparagine. The mutant can be reactivated using sodium azide, which essentially functions as a mobile proton donor.

Related Transporters: All Rhodopsins share the properties of a covalently bound retinal coupling light adsorption with ion translocation. There are several bacterial sensory Rhodopsins, such as the Cl- pumping Halorhodopsin, the Na+ pumping Rhodopsin KR2, Proteorhodopsin, which acts very similar to BR and Channelrhodopsin, which has a channel-like mechanism. Beside energy conversion they play key roles in phototaxis. Rhodopsins are also found in vertebrates, where they belong to the class of G protein-coupled receptors. Here, they are commonly found in light-sensing organs and responsible for the eyesight in humans.

Data and Applications

BR – pH dependence on the SURFE2R N1

BR pH dependence Slider

Icon N1   SURFE2R N1 data and applications:

Light induced currents have been measured at different pH values. Proton translocation depends on proton binding and release which show apparent pK values of > 10.5 and 4.9 respectively.

BR – different light intensities on the SURFE2R N1

BR Figure 2  intensity

Icon N1   SURFE2R N1 data and applications:

Light induced currents have been measured at different light intensities. The SURFE2R N1 SOLs standard green LED is able to satturate BR activity at ~ 100 mA.




BR – Action vs. Absorption Spectra on SURFE2R N1

BR Figure 2  wavelength

Icon N1   SURFE2R N1 data and applications:

Light induced currents have been measured using five LED sensor plates with different emission wavelengths. The wavelength dependent peak currents (action spectra) overlay with the absorption spectrum of BR






Posters

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Publications

2002 - Photocurrents Generated by Bacteriorhodopsin Adsorbed on Thiol/Lipid Bilayers Supported by Mercury

Icon N1   SURFE²R-technology (custom-built system) publication in Langmuir (2002)

Authors:
Dolfi A., Tadini-Buoninsegni F., Moncelli M.R., Guidelli R.

1993 - Charge transport by ion translocating membrane proteins on solid supported membranes

Icon N1   SURFE²R-technology (custom-built system) publication in Biophysical Journal (1993)

Authors:
Seifert K., Fendler K., Bamberg E.

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