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Sequential Unfolding of Individual Helices of Bacterioopsin Observed in Molecular Dynamics Simulations of Extraction from the Purple Membrane
- Source :
- Biophysical Journal. 91(9):3276-3284
- Publication Year :
- 2006
- Publisher :
- Elsevier BV, 2006.
-
Abstract
- Multiple molecular dynamics simulations of bacterioopsin pulling from its C-terminus show that its a-helices unfold individually. In the first metastable state observed in the simulations, helix G is unfolded at its C-terminal segment while the rest of helix G (residues 200-216) is folded and opposes resistance because of a salt-bridge network consisting of Asp-212 and Lys-216 on helix G and Arg-82 and Asp-85 on helix C. Helix G unfolds inside the bundle because the external force is applied to its C-terminal end in a direction perpendicular to the surface of the membrane. Inversely, helix F has to flip by 180° to exit from the membrane because the applied force and the helical N-C axis point in opposite directions. At the highest peak of the force, which cannot be interpreted in single-molecule force spectroscopy experiments, helix F has a pronounced kink at Pro-186. Mutation of Pro-186 and/or the charged side chains mentioned above, which are involved in very favorable electrostatic interactions in the low-dielectric region of the membrane, are expected to reduce the highest peak of the force. Helices E and D unfold in a similar way to helices G and F, respectively. Hence, the force-distance profile and sequence of events during forced unfolding of bacterioopsin are influenced by the up-and-down topology of the seven-helix bundle. The sequential extraction of individual helices from the membrane suggests that the spontaneous (un)folding of bacterioopsin proceeds through metastable bundles of fewer than seven helices. The metastable states observed in the simulations provide atomic level evidence that corroborates the interpretation of very recent force spectroscopy experiments of bacteriorhodopsin refolding. © 2006 by the Biophysical Society.
- Subjects :
- Models, Molecular
Protein Denaturation
Protein Folding
Molecular simulations
mechanical unfolding
membrane proteins
Protein Conformation
Biophysics
Motion
Molecular dynamics
Protein structure
Purple Membrane
Computer Simulation
bacterioopsin, molecular dynamics
Membranes
biology
Chemistry
Force spectroscopy
Bacteriorhodopsin
Elasticity
Folding (chemistry)
Kinetics
Crystallography
Models, Chemical
Bacteriorhodopsins
Helix
biology.protein
Protein folding
Stress, Mechanical
Triple helix
Subjects
Details
- ISSN :
- 00063495
- Volume :
- 91
- Issue :
- 9
- Database :
- OpenAIRE
- Journal :
- Biophysical Journal
- Accession number :
- edsair.doi.dedup.....154bb0aa672109b90f694770418bea31
- Full Text :
- https://doi.org/10.1529/biophysj.106.088591