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Most organisms use photoreceptors to sense and respond to light. Examples of photoreceptors include bacteriorhodopsins and bacteriophytochromes in some bacteria, phytochromes in plants, and rhodopsins in the photoreceptor cells of the vertebral retina. The light-sensitive property of these receptors is because of the bound chromophores, such as bilin in the phytochromes and retinal in the rhodopsins.
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Updated: May 7, 2026

Proton Transfer and Protein Conformation Dynamics in Photosensitive Proteins by Time-resolved Step-scan Fourier-transform Infrared Spectroscopy
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Intramolecular seal against proton backflow in bacteriorhodopsin.

Zhong Ren1,2

  • 1Department of Chemistry, University of Illinois Chicago, Chicago, IL 60607, USA.

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Light-driven proton pumps use an intramolecular seal to prevent backflow. This study visualizes intermediate states of bacteriorhodopsin, revealing the mechanism of this crucial proton transport.

Keywords:
BiophysicsCrystallographyStructural biology

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Microbiology

Background:

  • Microorganisms utilize light energy to create electrochemical gradients via proton pumps.
  • These pumps must overcome molecular-level backflow to maintain the gradient.

Purpose of the Study:

  • To elucidate the molecular mechanism of proton pumping in bacteriorhodopsin.
  • To resolve structural heterogeneity and visualize intermediate states of the proton pump.

Main Methods:

  • Utilized femtosecond serial crystallography to analyze structural data.
  • Unscrambled mixed structural signals to improve electron density maps.

Main Results:

  • Provided clear visualization of isolated intermediate states (I to M) in bacteriorhodopsin.
  • Revealed the motion of an intramolecular seal that partitions cellular channels.
  • Demonstrated how the seal prevents proton backflow.

Conclusions:

  • The intramolecular seal is key to preventing proton backflow during light-driven pumping.
  • Understanding bacteriorhodopsin's mechanism offers insights into bioenergetics and ion transport.