title: Molecular Interactions of Lipopolysaccharide with an Outer Membrane Protein from Pseudomonas aeruginosa Probed by Solution NMR.
abstract: Pseudomonas aeruginosa is an opportunistic human pathogen causing pneumonias that are particularly severe in cystic fibrosis and immunocompromised patients. The outer membrane (OM) of P. aeruginosa is much less permeable to nutrients and other chemical compounds than that of Escherichia coli. The low permeability of the OM, which also contributes to Pseudomonas' significant antibiotic resistance, is augmented by the presence of the outer membrane protein H (OprH). OprH directly interacts with lipopolysaccharides (LPS) that constitute the outer leaflet of the OM and thus contributes to the structural stability of the OM. In this study, we used solution NMR spectroscopy to characterize the interactions between LPS and OprH in molecular detail. NMR chemical shift perturbations observed upon the addition of LPS to OprH in DHPC micelles indicate that this interaction is predominantly electrostatic and localized to the extracellular loops 2 and 3 and a number of highly conserved basic residues near the extracellular barrel rim of OprH. Single-site mutations of these residues were not enough to completely abolish binding, but OprH with cumulative mutations of Lys70, Arg72, and Lys103 no longer binds LPS. The dissociation constant (∼200 μM) measured by NMR is sufficient to efficiently bind LPS to OprH in the OM. This work highlights that solution NMR is suitable to study specific interactions of lipids with integral membrane proteins and provides a detailed molecular model for the interaction of LPS with OprH; i.e., an interaction that contributes to the integrity of the OM of P. aeruginosa under low divalent cation and antibiotic stress conditions. These methods should thus be useful for screening antibiotics that might disrupt OprH-LPS interactions and thereby increase the permeability of the OM of P. aeruginosa.
authors.affiliation: Center for Membrane and Cell Physiology and Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine , Charlottesville, Virginia 22908, United States.
authors.forename: Iga
authors.initials: I
authors.lastname: Kucharska
authors.affiliation: Center for Membrane and Cell Physiology and Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine , Charlottesville, Virginia 22908, United States.
authors.forename: Binyong
authors.initials: B
authors.lastname: Liang
authors.affiliation: Center for Membrane and Cell Physiology and Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine , Charlottesville, Virginia 22908, United States.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Ursini
authors.affiliation: Center for Membrane and Cell Physiology and Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine , Charlottesville, Virginia 22908, United States.
authors.forename: Lukas K
authors.initials: LK
authors.lastname: Tamm
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D008070:Lipopolysaccharides / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D017510:Protein Folding; D011550:Pseudomonas aeruginosa / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D001425:Bacterial Outer Membrane Proteins; D008070:Lipopolysaccharides