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Proton Transfer and Protein Conformation Dynamics in Photosensitive Proteins by Time-resolved Step-scan Fourier-transform Infrared Spectroscopy
Published on: June 27, 2014
Time-resolved WAXS reveals accelerated conformational changes in iodoretinal-substituted proteorhodopsin
Erik Malmerberg1, Ziad Omran, Jochen S Hub
1Department of Chemistry, Biochemistry and Biophysics, University of Gothenburg, Gothenburg, Sweden.
Biophysical Journal
|September 28, 2011
Summary
Time-resolved wide-angle x-ray scattering (TR-WAXS) reveals protein dynamics. Halogenating proteorhodopsin (pR) accelerates its photocycle and structural changes, yet the main transient conformation remains unaffected.
Area of Science:
- Biophysics
- Structural Biology
- Photochemistry
Background:
- Proteorhodopsins (pR) are light-driven proton pumps.
- Understanding their conformational changes is key to their function.
- Time-resolved wide-angle x-ray scattering (TR-WAXS) is a powerful technique for observing these dynamics.
Purpose of the Study:
- To compare the dynamics of native proteorhodopsin (SAR86) with a halogenated derivative (13-I-pR).
- To investigate the effect of retinal chromophore substitution on protein conformational changes.
- To elucidate the impact of iodination on the photocycle kinetics and structural rearrangements.
Main Methods:
- Comparative time-resolved wide-angle x-ray scattering (TR-WAXS).
- Transient absorption spectroscopy.
- Molecular dynamics simulations.
Main Results:
- The 13-I-pR photocycle is accelerated and kinetically more complex than native pR.
- Protein structural changes in 13-I-pR occur an order-of-magnitude faster.
- Helical motion amplitude and nature are largely preserved despite C-20 methyl to iodine substitution.
- Simulations show increased free energy for the 13-cis conformation of 13-I-pR.
Conclusions:
- Retinal iodination significantly accelerates the conformational trajectory of proteorhodopsin.
- The major transient conformation populated during the photocycle is not significantly altered by the iodinated retinal.
- TR-WAXS and spectroscopy provide insights into light-driven protein dynamics.
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