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Photoisomerization in proteorhodopsin mutant D97N
Martin O Lenz1, Andreas C Woerner, Clemens Glaubitz
1Institute for Physical and Theoretical Chemistry, Johann Wolfgang Goethe-Universität Frankfurt, Germany.
Photochemistry and Photobiology
|July 1, 2006
Summary
The D97N proteorhodopsin (PR) mutant
Area of Science:
- Biochemistry
- Spectroscopy
- Molecular Biology
Background:
- Proteorhodopsin (PR) is a light-driven proton pump.
- Understanding its photocycle is crucial for bioenergetics.
- Mutant studies reveal functional mechanisms.
Purpose of the Study:
- Investigate the initial photocycle steps of the D97N PR mutant.
- Compare its dynamics to native PR and bacteriorhodopsin mutants.
- Elucidate the role of Asp97 in ultrafast isomerization.
Main Methods:
- Ultrafast transient absorption spectroscopy.
- Photocycle analysis of proteorhodopsin mutants.
- Comparative dynamics studies.
Main Results:
- Excited state decay is biexponential (1.4 and 20 ps) via a conical intersection.
- This leads to 13-cis isomerized retinal.
- Dynamics are slower than native PR, even at pH 6.
Conclusions:
- Ultrafast isomerization is influenced by factors beyond retinal pocket electrostatics.
- Steric interactions and water molecules may play a role in Asp97's function.
- Asp97's catalytic role in PR isomerization is complex.