title: pH-dependent interactions guide the folding and gate the transmembrane pore of the beta-barrel membrane protein OmpG.
abstract: The physical interactions that switch the functional state of membrane proteins are poorly understood. Previously, the pH-gating conformations of the beta-barrel forming outer membrane protein G (OmpG) from Escherichia coli have been solved. When the pH changes from neutral to acidic the flexible extracellular loop L6 folds into and closes the OmpG pore. Here, we used single-molecule force spectroscopy to structurally localize and quantify the interactions that are associated with the pH-dependent closure. At acidic pH, we detected a pH-dependent interaction at loop L6. This interaction changed the (un)folding of loop L6 and of beta-strands 11 and 12, which connect loop L6. All other interactions detected within OmpG were unaffected by changes in pH. These results provide a quantitative and mechanistic explanation of how pH-dependent interactions change the folding of a peptide loop to gate the transmembrane pore. They further demonstrate how the stability of OmpG is optimized so that pH changes modify only those interactions necessary to gate the transmembrane pore.
authors.affiliation: Biotechnology Center, University of Technology, Tatzberg 47, 01307 Dresden, Germany.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Damaghi
authors.forename: Christian
authors.initials: C
authors.lastname: Bippes
authors.forename: Stefan
authors.initials: S
authors.lastname: Köster
authors.forename: Ozkan
authors.initials: O
authors.lastname: Yildiz
authors.forename: Stefania A
authors.initials: SA
authors.lastname: Mari
authors.forename: Werner
authors.initials: W
authors.lastname: Kühlbrandt
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Muller
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D008954:Models, Biological; D008956:Models, Chemical; D018272:Porins / Q000737:chemistry* / Q000378:metabolism*; D017510:Protein Folding; D013057:Spectrum Analysis / Q000379:methods
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; C114347:OmpG protein, E coli; D018272:Porins