title: Ligand-specific opening of a gated-porin channel in the outer membrane of living bacteria.
abstract: Ligand-gated membrane channels selectively facilitate the entry of iron into prokaryotic cells. The essential role of iron in metabolism makes its acquisition a determinant of bacterial pathogenesis and a target for therapeutic strategies. In Gram-negative bacteria, TonB-dependent outer membrane proteins form energized, gated pores that bind iron chelates (siderophores) and internalize them. The time-resolved operation of the Escherichia coli ferric enterobactin receptor FepA was observed in vivo with electron spin resonance spectroscopy by monitoring the mobility of covalently bound nitroxide spin labels. A ligand-binding surface loop of FepA, which normally closes its transmembrane channel, exhibited energy-dependent structural changes during iron and toxin (colicin) transport. These changes were not merely associated with ligand binding, but occurred during ligand uptake through the outer membrane bilayer. The results demonstrate by a physical method that gated-porin channels open and close during membrane transport in vivo.
authors.affiliation: Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019, USA.
authors.forename: X
authors.initials: X
authors.lastname: Jiang
authors.forename: M A
authors.initials: MA
authors.lastname: Payne
authors.forename: Z
authors.initials: Z
authors.lastname: Cao
authors.forename: S B
authors.initials: SB
authors.lastname: Foster
authors.forename: J B
authors.initials: JB
authors.lastname: Feix
authors.forename: S M
authors.initials: SM
authors.lastname: Newton
authors.forename: P E
authors.initials: PE
authors.lastname: Klebba
mesh_terms: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D003087:Colicins / Q000494:pharmacology; D003497:Cyclic N-Oxides; D003545:Cysteine / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004758:Enterobactin / Q000378:metabolism* / Q000494:pharmacology; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005290:Ferric Compounds / Q000378:metabolism / Q000494:pharmacology; D007202:Indicators and Reagents; D015640:Ion Channel Gating; D008024:Ligands; D008565:Membrane Proteins / Q000378:metabolism; D008698:Mesylates; D018272:Porins / Q000378:metabolism*; D011487:Protein Conformation; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013113:Spin Labels
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D003087:Colicins; D003497:Cyclic N-Oxides; D029968:Escherichia coli Proteins; D005290:Ferric Compounds; D007202:Indicators and Reagents; D008024:Ligands; D008565:Membrane Proteins; D008698:Mesylates; D018272:Porins; D011956:Receptors, Cell Surface; D013113:Spin Labels; C029489:enterobactin receptor; C057616:tonB protein, Bacteria; C489181:tonB protein, E coli; C017480:4-maleimido-2,2,6,6-tetramethylpiperidinooxyl; D004758:Enterobactin; C074502:methanethiosulfonate; D003545:Cysteine