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Unfolding pathways of individual bacteriorhodopsins
F Oesterhelt1, D Oesterhelt, M Pfeiffer
1CeNS and Lehrstuhl für angewandte Physik, Ludwig Maximilians-Universität München, Amalienstrasse 54, 80799 München, Germany.
Science (New York, N.Y.)
|February 7, 2001
Summary
Atomic force microscopy revealed how individual bacteriorhodopsin molecules are anchored in purple membranes. Unfolding pathways showed unique helix interactions, with helix B stabilized by neighbors.
Area of Science:
- Biophysics
- Structural Biology
- Membrane Protein Dynamics
Background:
- Purple membranes from Halobacterium salinarum contain bacteriorhodopsin, a key light-driven proton pump.
- Understanding the mechanical properties and interactions of membrane proteins is crucial for their function.
Purpose of the Study:
- To investigate the anchoring forces and unfolding mechanisms of individual bacteriorhodopsin helices.
- To elucidate the role of inter-helical interactions in protein stability and unfolding pathways.
Main Methods:
- Combined atomic force microscopy (AFM) and single-molecule force spectroscopy (SMFS).
- Localized and extracted individual bacteriorhodopsin molecules from purple membrane patches.
- Imaged vacancies and analyzed force spectra during helix unfolding.
Main Results:
- Determined anchoring forces for different helices (100-200 piconewtons).
- Observed distinct, individual unfolding pathways for bacteriorhodopsin helices.
- Identified pairwise unfolding of helices (G/F, E/D) and sequential unfolding (B/C).
- Demonstrated stabilization of helix B by neighboring helices through experiments with cleaved loops.
Conclusions:
- Bacteriorhodopsin helix unfolding is a complex process with individual pathways.
- Inter-helical interactions significantly contribute to protein stability and mechanical properties.
- AFM and SMFS are powerful tools for probing single-molecule mechanics in biological membranes.
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