Spontaneous formation of detergent micelles around the outer membrane protein OmpX

TitleSpontaneous formation of detergent micelles around the outer membrane protein OmpX
Publication TypeJournal Article
Year of Publication2005
AuthorsBöckmann R.A, Caflisch A.
JournalBiophysical Journal
Volume88
Issue5
Pagination3191-3204
Date Published2005 May
Type of ArticleResearch Article
ISSN0006-3495
KeywordsBacterial Outer Membrane Proteins, Computer Simulation, Detergents, Escherichia coli, Escherichia coli Proteins, Hydrolases, Lipids, Magnetic Resonance Spectroscopy, Micelles, Models, Molecular, Models, Statistical, Phosphatidylcholines, Phospholipid Ethers, Protein Binding, Protein Conformation, Protein Structure, Secondary, Proteins, Solvents, Surface Properties, Time Factors, Water
Abstract

The structure and flexibility of the outer membrane protein X (OmpX) in a water-detergent solution and in pure water are investigated by molecular dynamics simulations on the 100-ns timescale and compared with NMR data. The simulations allow for an unbiased determination of the structure of detergent micelles and the protein-detergent mixed micelle. The short-chain lipid dihexanoylphosphatidylcholine, as a detergent, aggregates into pure micelles of approximately 18 molecules, or alternatively, it binds to the protein surface. The detergent binds in the form of a monolayer ring around the hydrophobic β-barrel of OmpX rather than in a micellar-like oblate; approximately 40 dihexanoylphosphatidylcholine lipids are sufficient for an effective suppression of water from the surface of the beta-barrel region. The phospholipids bind also on the extracellular, protruding β-sheet. Here, polar interactions between charged amino acids and phosphatidylcholine headgroups act as condensation seed for detergent micelle formation. The polar protein surface remains accessible to water molecules. In total, approximately 90-100 detergent molecules associate within the protein-detergent mixed micelle, in agreement with experimental estimates. The simulation results indicate that OmpX is not a water pore and support the proposed role of the protruding β-sheet as a "fishing rod".

DOI10.1529/biophysj.105.060426
pubindex

0065

Alternate JournalBiophys. J.
PubMed ID15749771
PubMed Central IDPMC1305469
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