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Updated: May 23, 2026

Photobleaching Enables Super-resolution Imaging of the FtsZ Ring in the Cyanobacterium Prochlorococcus
Published on: November 6, 2018
Structural changes in bacteriorhodopsin caused by two-photon-induced photobleaching.
Daniel Rhinow1, Martin Imhof, Ivan Chizhik
1Department of Structural Biology, Max-Planck-Institute of Biophysics, Max-von-Laue-Str. 3, D-60438 Frankfurt, Germany.
Two-photon absorption (TPA) in bacteriorhodopsin (BR) causes structural changes and irreversible Schiff base reduction. This leads to loss of purple membrane (PM) crystalline order and permanent BR shape changes.
Area of Science:
- Biophysics
- Structural Biology
- Photochemistry
Background:
- Bacteriorhodopsin (BR) is a light-driven proton pump in halobacteria, forming purple membranes (PM).
- The two-photon absorption (TPA) mechanism and its structural consequences in BR remain poorly understood despite high reported TPA cross sections.
Purpose of the Study:
- To investigate the structural and photochemical effects of TPA on bacteriorhodopsin (BR) and purple membranes (PM).
- To elucidate the molecular mechanisms underlying BR's TPA response and its irreversibility.
Main Methods:
- Spectroscopy (FTIR, CD)
- Small-angle X-ray scattering (SAXS)
- Electron microscopy
- Atomic force microscopy (AFM)
Main Results:
- TPA induces an UV-absorbing N-retinyl-bacterioopsin state and loss of PM crystalline order.
- BR trimers and secondary structure are preserved, but TPA causes photochemical reduction of the retinal Schiff base.
- This reduction leads to a permanent asymmetric shape change in BR, causing PM sheets to roll up and lose crystallinity.
Conclusions:
- TPA induces irreversible structural changes in BR via Schiff base reduction.
- The observed shape change in BR disrupts PM crystalline order, providing a model for TPA photoresponse.
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