Page 24 - ILLS Annual Report 2018

BIOLOGY AND HEALTH
Emanuel Schneck. German
Biomaterials Department, Max Planck Institute of Colloids and Interfaces, Potsdam
‘Neutron reflectometry is the ideal tool for the structural characterisation of complex biomolecular layers with high depth resolution.’
Sugar polymers at the outermost surface of bacteria
Vertical reflectometer D17
Lipopolysaccharide (LPS) molecules form the outer surfaces of Gram-negative bacteria, where they expose oligo- and polysaccharides to the aqueous environment. This structurally complex molecular layer is of great scientific interest as it mediates the interaction of bacteria with antimicrobial agents as well as neighbouring bacteria in colonies. Structural studies on LPS surfaces, however, have to
date used chemically simple LPS molecules, so-called rough mutant LPS. Here, by using neutron reflectometry (NR), we have structurally characterised monolayers of wild-type LPS form featuring strain-specific O-side chains in contact with aqueous solutions and under controlled interaction conditions. The model used for the reflectivity analysis gave access to the volume fraction profiles of all the chemical components. The saccharide profiles were found to be bimodal, with dense inner oligosaccharides and more dilute, extended O-side chains. For interacting LPS monolayers, NR revealed the distance-dependent saccharide conformation.
Figure 1
top) Schematic illustration of a single, solid-supported LPS monolayer in aqueous buffer. The solid surface is hydrophobically functionalised with octadecyltrichlorosilane. All LPS molecules comprise the inner oligosaccharide, while only a certain fraction display O-side chains.
bottom) Schematic illustration of two interacting LPS monolayers in a double-monolayer configuration.
AUTHORS
E. Schneck, I. Rodriguez Loureiro and V.M. Latza
(Max Planck Institute of Colloids and Interfaces, Potsdam, Germany) G. Fragneto (ILL)
ARTICLE FROM
Biophys. J. (2018)—doi: 10.1016/j.bpj.2018.02.014
REFERENCES
[1] C. Erridge, E. Bennett-Guerrero and I.R. Poxton, Microbes Infect. 4 (2002) 837
[2] E. Schneck, T. Schubert, O.V. Konovalov, B. Quinn, T. Gutsmann, K. Brandenburg, R.G. Oliveira, D. Pink and M. Tanaka,
Proc. Natl. Acad. Sci. USA 107 (2010) 9147
[3] L.A. Clifton, S.A. Holt, A.V. Hughes, E.L. Daulton, W. Arunmanee, F. Heinrich, S. Khalid, D. Jefferies, T.R. Charlton, J.R.P. Webster, C.J. Kinane and J.H. Lakey, Angew. Chem. Int. Ed. 54
(2015) 11952
[4] I. Rodriguez Loureiro, V.M. Latza, G. Fragneto and E. Schneck, Biophys. J. 114 (2018) 1264
Lipopolysaccharides (LPSs) are the main constituents
of the outer monolayer of the Gram-negative bacterial outer membrane [1]. They govern the mutual interaction between neighbouring bacteria in colonies and (undesired) biofilms, and act as protection against harmful molecules. This protection is weakened, however, when divalent cations such as calcium or magnesium are absent from the aqueous environment.
LPS molecules consist of an extremely invariant part that
is itself constituted of four to seven hydrocarbon chains and a headgroup composed of the inner oligosaccharide (8-12 sugar rings) that carries a negative net charge.
A certain fraction of LPS molecules possess strain-specific O-side chains (OSC) in the form of repetitive oligosaccharide motifs.
The considerable biomedical relevance of Gram-negative bacterial outer-surfaces has motivated numerous structural investigations of LPS layers by X-ray and neutron scattering techniques [2, 3]. These studies have, however, to date dealt almost exclusively with rough mutant LPSs, neglecting the OSC as an important feature of most bacterial surfaces.
ANNUAL REPORT 2018