title: Membrane thickness varies around the circumference of the transmembrane protein BtuB.
abstract: BtuB is a large outer-membrane β-barrel protein that belongs to a class of active transport proteins that are TonB-dependent. These TonB-dependent transporters are based upon a 22-stranded antiparallel β-barrel, which is notably asymmetric in its length. Here, site-directed spin labeling and simulated annealing were used to locate the membrane lipid interface surrounding BtuB when reconstituted into phosphatidylcholine bilayers. Positions on the outer facing surface of the β-barrel and the periplasmic turns were spin-labeled and distances from the label to the membrane interface estimated by progressive power saturation of the electron paramagnetic resonance spectra. These distances were then used as atom-to-plane distance restraints in a simulated annealing routine, to dock the protein to two independent planes and produce a model representing the average position of the lipid phosphorus atoms at each interface. The model is in good agreement with the experimental data; however, BtuB is mismatched to the bilayer thickness and the resulting planes representing the bilayer interface are not parallel. In the model, the membrane thickness varies by 11 Å around the circumference of the protein, indicating that BtuB distorts the bilayer interface so that it is thinnest on the short side of the protein β-barrel.
authors.affiliation: Department of Chemistry and Center for Membrane Biology at the University of Virginia, Charlottesville, Virginia, USA.
authors.forename: Jeffrey F
authors.initials: JF
authors.lastname: Ellena
authors.forename: Pawel
authors.initials: P
authors.lastname: Lackowicz
authors.forename: Hillary
authors.initials: H
authors.lastname: Mongomery
authors.forename: David S
authors.initials: DS
authors.lastname: Cafiso
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism; D004926:Escherichia coli; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D010713:Phosphatidylcholines / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D012997:Solvents / Q000737:chemistry
chemical_list: D001425:Bacterial Outer Membrane Proteins; C044592:BtuB protein, E coli; D029968:Escherichia coli Proteins; D008051:Lipid Bilayers; D026901:Membrane Transport Proteins; D010713:Phosphatidylcholines; D012997:Solvents; C028694:1-palmitoyl-2-oleoylphosphatidylcholine