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Related Experiment Videos

Protein conformational changes in the bacteriorhodopsin photocycle.

S Subramaniam1, M Lindahl, P Bullough

  • 1MRC Laboratory for Molecular Biology, Cambridge, England. sriram@mrc-lmb.cam.ac.uk

Journal of Molecular Biology
|March 13, 1999
PubMed
Summary

Electron crystallography reveals a single, fundamental conformational change in bacteriorhodopsin

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Area of Science:

  • Structural Biology
  • Biophysics
  • Protein Dynamics

Background:

  • Bacteriorhodopsin is a light-driven proton pump crucial for energy transduction.
  • Understanding its photocycle and conformational changes is key to elucidating its mechanism.
  • Mutations can trap specific photocycle intermediates, offering insights into structural dynamics.

Purpose of the Study:

  • To comprehensively analyze conformational changes in wild-type and mutant bacteriorhodopsin during its photocycle using electron crystallography.
  • To determine the structural basis for kinetic defects in various bacteriorhodopsin mutants.
  • To elucidate the relationship between structural changes and photocycle intermediates.

Main Methods:

  • Electron crystallography of flash-illuminated wild-type and mutant bacteriorhodopsin crystals.

Related Experiment Videos

  • Trapping of photocycle intermediates by rapid freezing.
  • Construction of projection difference Fourier maps at 3.5 Å resolution.

    • Main Results:

    • A significant protein conformational change occurs within 1 ms after light activation in wild-type bacteriorhodopsin.
    • Structural differences between M and N intermediates are small in the same protein but vary significantly across different mutants.
    • Mutations can induce partial or full conformational changes even in the dark.

    Conclusions:

    • Observed structural changes in mutants with long-lived intermediates represent variations of a single fundamental conformational change.
    • The photocycle involves two main protein conformations, approximating early (K, L, M1) and late (M2, N, O) intermediates.
    • This conformational change is critical for switching Schiff base proton accessibility during proton pumping.