Effect of divalent cation removal on the structure of gram-negative bacterial outer membrane models

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dc.contributor.authorClifton, LAen_AU
dc.contributor.authorSkoda, MWAen_AU
dc.contributor.authorLe Brun, APen_AU
dc.contributor.authorCiesielski, Fen_AU
dc.contributor.authorKuzmenko, Ien_AU
dc.contributor.authorHolt, SAen_AU
dc.contributor.authorLakey, JHen_AU
dc.date.accessioned2024-10-03T23:14:23Zen_AU
dc.date.available2024-10-03T23:14:23Zen_AU
dc.date.issued2015-01-13en_AU
dc.date.statistics2024-08-28en_AU
dc.description.abstractThe Gram-negative bacterial outer membrane (GNB-OM) is asymmetric in its lipid composition with a phospholipid-rich inner leaflet and an outer leaflet predominantly composed of lipopolysaccharides (LPS). LPS are polyanionic molecules, with numerous phosphate groups present in the lipid A and core oligosaccharide regions. The repulsive forces due to accumulation of the negative charges are screened and bridged by the divalent cations (Mg2+ and Ca2+) that are known to be crucial for the integrity of the bacterial OM. Indeed, chelation of divalent cations is a well-established method to permeabilize Gram-negative bacteria such as Escherichia coli. Here, we use X-ray and neutron reflectivity (XRR and NR, respectively) techniques to examine the role of calcium ions in the stability of a model GNB-OM. Using XRR we show that Ca2+ binds to the core region of the rough mutant LPS (RaLPS) films, producing more ordered structures in comparison to divalent cation free monolayers. Using recently developed solid-supported models of the GNB-OM, we study the effect of calcium removal on the asymmetry of DPPC:RaLPS bilayers. We show that without the charge screening effect of divalent cations, the LPS is forced to overcome the thermodynamically unfavorable energy barrier and flip across the hydrophobic bilayer to minimize the repulsive electrostatic forces, resulting in about 20% mixing of LPS and DPPC between the inner and outer bilayer leaflets. These results reveal for the first time the molecular details behind the well-known mechanism of outer membrane stabilization by divalent cations. This confirms the relevance of the asymmetric models for future studies of outer membrane stability and antibiotic penetration. © 2014 American Chemical Society. This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.en_AU
dc.description.sponsorshipThis research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. This work was supported by ISIS beam-time award 1410126. J.H.L. wishes to thank the Wellcome Trust for support (Grant Nos. 080342 and 093581). A.P.L.B. thanks the Australian Research Council for a Discovery Early Career Researcher Award (DE140101788).en_AU
dc.format.mediumPrint-Electronicen_AU
dc.identifier.citationClifton, L. A., Skoda, M. W. A., Le Brun, A. P., Ciesielski, F., Kuzmenko, I., Holt, S. A., & Lakey, J. H. (2015). Effect of divalent cation removal on the structure of gramnegative bacterial outer membrane models. Langmuir, 31(1), 404-412. doi:10.1021/la504407ven_AU
dc.identifier.issn0743-7463en_AU
dc.identifier.issn1520-5827en_AU
dc.identifier.issue1en_AU
dc.identifier.journaltitleLangmuiren_AU
dc.identifier.pagination404-412en_AU
dc.identifier.urihttps://doi.org/10.1021/la504407ven_AU
dc.identifier.urihttps://apo.ansto.gov.au/handle/10238/15721en_AU
dc.identifier.volume31en_AU
dc.languageEnglishen_AU
dc.language.isoenen_AU
dc.publisherAmerican Chemical Societyen_AU
dc.subjectCationsen_AU
dc.subjectBacteriaen_AU
dc.subjectPhospholipidsen_AU
dc.subjectLipopolysaccharidesen_AU
dc.subjectMoleculesen_AU
dc.subjectOligosaccharidesen_AU
dc.subjectCalciumen_AU
dc.titleEffect of divalent cation removal on the structure of gram-negative bacterial outer membrane modelsen_AU
dc.typeJournal Articleen_AU
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