title: A minimal transmembrane beta-barrel platform protein studied by nuclear magnetic resonance.
abstract: In this study, we were concerned with the structural role of the surface-exposed extracellular loops of the N-terminal transmembrane (TM) domain of OmpA. A variant of the TM domain of outer membrane protein A (OmpA) with all four such loops shortened, which we call the beta-barrel platform (BBP), was successfully refolded. This indicates that the removed parts of the surface-exposed loops indeed do not contain amino acid sequences critical for this membrane protein's refolding in vitro. BBP has the potential to be used as a template beta-barrel membrane protein structure for the development of novel functions, although our results also highlight the potential difficulties that can arise when functionality is being engineered into the loop regions of membrane proteins. We have used solution nuclear magnetic resonance spectroscopy to determine the global fold of BBP+EF, BBP with a metal ion-binding EF-hand inserted in one of the shortened loops. BBP and BBP+EF in dihexanoylphosphatidylcholine micelles are eight-stranded antiparallel beta-barrels, and BBP represents the smallest beta-structured integral membrane protein known to date.
authors.affiliation: Laboratorium für Physikalische Chemie, ETH Hönggerberg, Wolfgang-Pauli-Strasse 10, CH-8093 Zürich, Switzerland. maria.johansson@nmr.gu.se
authors.forename: Maria U
authors.initials: MU
authors.lastname: Johansson
authors.forename: Simon
authors.initials: S
authors.lastname: Alioth
authors.forename: Kaifeng
authors.initials: K
authors.lastname: Hu
authors.forename: Reto
authors.initials: R
authors.lastname: Walser
authors.forename: Ralf
authors.initials: R
authors.lastname: Koebnik
authors.forename: Konstantin
authors.initials: K
authors.lastname: Pervushin
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry*; D020832:EF Hand Motifs / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008565:Membrane Proteins / Q000737:chemistry*; D008823:Micelles; D010713:Phosphatidylcholines; D017510:Protein Folding; D012996:Solutions
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D008823:Micelles; D010713:Phosphatidylcholines; D012996:Solutions; C078167:OMPA outer membrane proteins; C032166:1,2-hexanoylphosphatidylcholine