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Conformational changes in the core structure of bacteriorhodopsin
T Kluge1, J Olejnik, L Smilowitz
1Physics Department, Molecular Biophysics Laboratory, Boston University, Massachusetts 02215, USA.
Biochemistry
|July 17, 1998
Summary
Bacteriorhodopsin (bR) structural changes in its core were probed using deuterium exchange. Retinal isomerization triggers early conformational changes in the bR core, potentially strengthening alpha-helical hydrogen bonds.
Area of Science:
- Biophysics
- Structural Biology
- Spectroscopy
Background:
- Bacteriorhodopsin (bR) is a light-driven proton pump in Halobacterium salinarium.
- The core structure of bR is typically inaccessible to hydrogen/deuterium (H/D) exchange.
Purpose of the Study:
- To investigate structural changes in the inaccessible core of bR during its photocycle.
- To assign FTIR difference bands to peptide vibrations within the bR core.
Main Methods:
- Utilized Fourier Transform Infrared (FTIR) spectroscopy.
- Employed hydrogen/deuterium (H/D) exchange by reconstituting and regenerating delipidated bR in D2O.
- Analyzed low-temperature FTIR difference spectra of core-deuterated samples.
Main Results:
- Peripheral bR peptide NH groups showed partial H/D exchange, while core backbone structure underwent complete exchange when regenerated in D2O.
- Core-deuterated bR revealed that peptide groups in the core respond to retinal isomerization as early as the K intermediate.
- Significant structural changes in the bR core occur by the M intermediate, indicated by amide I and II band shifts.
Conclusions:
- Retinal isomerization induces early conformational changes in the bacteriorhodopsin core structure.
- These conformational changes may involve enhanced intramolecular alpha-helical hydrogen bonds.
- FTIR difference spectroscopy with H/D exchange is effective for probing inaccessible protein core structures.