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Bacteriorhodopsin is involved in halobacterial photoreception
S I Bibikov1, R N Grishanin, A D Kaulen
1A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russia.
Summary
Bacteriorhodopsin (BR) gene introduction enabled a blind Halobacterium salinarium mutant to sense light. The study shows BR-mediated photoreception relies on light-dependent generation of proton motive force (delta mu H+).
Area of Science:
- Microbiology
- Biophysics
- Molecular Biology
Background:
- Halobacterium salinarium utilizes retinal proteins for phototaxis.
- A specific mutant lacked all retinal proteins, rendering it blind.
- Understanding the function of bacteriorhodopsin (BR) in light sensing is crucial.
Purpose of the Study:
- To investigate the role of bacteriorhodopsin (BR) in light sensing and phototaxis.
- To determine if BR can restore light sensitivity in a 'blind' mutant.
- To elucidate the mechanism of BR-mediated photoreception.
Main Methods:
- Genetic transformation of Halobacterium salinarium with the bacterio-opsin gene.
- Behavioral assays to assess phototactic responses (attraction and repulsion).
- Biochemical analysis of proton motive force (delta mu H+) generation and its modulation.
Main Results:
- Transformed cells exhibited BR-mediated orientation in spatial light gradients.
- Light intensity changes elicited attractant and repellent responses, with some differences from wild-type.
- BR-mediated responses were linked to light-dependent generation of delta mu H+ and modulated by chemical agents.
- Mutant BR D96N showed reduced responses, indicating the importance of proton pump activity.
Conclusions:
- Bacteriorhodopsin (BR) mediates photoreception in Halobacterium salinarium through light-dependent generation of proton motive force (delta mu H+).
- The cell likely monitors membrane energization levels via a 'protometer' system.
- BR's role in phototaxis is confirmed, distinct yet comparable in some aspects to sensory rhodopsins.