Related Experiment Videos
Lipid location in deoxycholate-treated purple membrane at 2.6 A
N Grigorieff1, E Beckmann, F Zemlin
1MRC Laboratory of Molecular Biology, Cambridge, UK.
Journal of Molecular Biology
|December 1, 1995
Summary
High-resolution imaging of deoxycholate-treated purple membrane reveals structural identity with native forms. This study identifies six lipids per bacteriorhodopsin molecule, suggesting strong electrostatic interactions stabilize the crystal structure.
Area of Science:
- Structural biology
- Biophysics
- Membrane protein structure
Background:
- Purple membrane contains bacteriorhodopsin, a light-driven proton pump crucial for energy transduction.
- Understanding bacteriorhodopsin's structure and lipid interactions is key to elucidating its function.
Purpose of the Study:
- To determine the high-resolution structure of deoxycholate-treated purple membrane.
- To compare the structure of native and treated purple membrane.
- To identify the role and number of lipids associated with bacteriorhodopsin.
Main Methods:
- High-resolution cryo-electron microscopy (2.6 Å resolution) using a 200 keV FEG microscope.
- Analysis of projection maps combined with atomic models of bacteriorhodopsin.
- Comparison of crystal lattice parameters and lipid content.
Main Results:
- Deoxycholate treatment resulted in a reduced cell dimension and loss of approximately half the native lipids.
- The internal trimer structure of bacteriorhodopsin remained largely identical between native and treated forms.
- Six lipids per bacteriorhodopsin molecule were identified in the treated crystal form, with three in conserved positions.
Conclusions:
- Bacteriorhodopsin trimers act as rigid bodies with minimal rotation despite significant changes in crystal contacts.
- Strong, long-range electrostatic interactions likely stabilize the purple membrane crystal lattice.
- The identified lipid stoichiometry provides insights into membrane protein-lipid interactions.