title: LptE binds to and alters the physical state of LPS to catalyze its assembly at the cell surface.
abstract: The assembly of lipopolysaccharide (LPS) on the surface of Gram-negative bacterial cells is essential for their viability and is achieved by the seven-protein LPS transport (Lpt) pathway. The outer membrane (OM) lipoprotein LptE and the β-barrel membrane protein LptD form a complex that assembles LPS into the outer leaflet of the OM. We report a crystal structure of the Escherichia coli OM lipoprotein LptE at 2.34 Å. The structure reveals homology to eukaryotic LPS-binding proteins and allowed for the prediction of an LPS-binding site, which was confirmed by genetic and biophysical experiments. Specific point mutations at this site lead to defects in OM biogenesis. We show that wild-type LptE disrupts LPS-LPS interactions in vitro and that these mutations decrease the ability of LptE to disaggregate LPS. Transmission electron microscopic imaging shows that LptE can disrupt LPS aggregates even at substoichiometric concentrations. We propose a model in which LptE functions as an LPS transfer protein in the OM translocon by disaggregating LPS during transport to allow for its insertion into the OM.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138;
authors.forename: Goran
authors.initials: G
authors.lastname: Malojčić
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138;
authors.forename: Dorothee
authors.initials: D
authors.lastname: Andres
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ 08544;
authors.forename: Marcin
authors.initials: M
authors.lastname: Grabowicz
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138;
authors.forename: Alexander H
authors.initials: AH
authors.lastname: George
authors.affiliation: Department of Microbiology, The Ohio State University, Columbus, OH 43210; and.
authors.forename: Natividad
authors.initials: N
authors.lastname: Ruiz
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ 08544; tsilhavy@princeton.edu kahne@chemistry.harvard.edu.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Silhavy
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138;Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, MA 02115 tsilhavy@princeton.edu kahne@chemistry.harvard.edu.
authors.forename: Daniel
authors.initials: D
authors.lastname: Kahne
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D001692:Biological Transport / Q000502:physiology; D002384:Catalysis; D003460:Crystallization; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D008070:Lipopolysaccharides; C475958:LptD protein, E coli; C514179:LptE protein, E coli; D046912:Multiprotein Complexes
keywords: endotoxin; glycolipid binding; membrane asymmetry; membrane biogenesis; vesicles