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Lipopolysaccharide (LPS) is a crucial constituent of the outer membrane of most Gram-negative bacteria, playing a fundamental role in the protection of bacteria from environmental stress factors, in drug resistance, in pathogenesis, and in symbiosis. During the last decades, LPS has been thoroughly dissected, and massive information on this fascinating biomolecule is now available. In this Review, we will give the reader a third millennium update of the current knowledge of LPS with key information on the inherent peculiar carbohydrate chemistry due to often puzzling sugar residues that are uniquely found on it. Then, we will drive the reader through the complex and multifarious immunological outcomes that any given LPS can raise, which is strictly dependent on its chemical structure. Further, we will argue about issues that still remain unresolved and that would represent the immediate future of LPS research. It is critical to address these points to complete our notions on LPS chemistry, functions, and roles, in turn leading to innovative ways to manipulate the processes involving such a still controversial and intriguing biomolecule.

Lipopolysaccharide, LPS, structure, Pathogenesis, carbohydrate, function, gram negative bacteria

NCBI PubMed ID: 34286971
Publication DOI: 10.1021/acs.chemrev.0c01321
Journal NLM ID: 2985134R
Publisher: Chem Rev
Correspondence: Antonio Molinaro
Institutions: Department of Chemical Sciences, University of Naples Federico II, via Cinthia 4, 80126 Naples, Italy, Task Force on Microbiome Studies, University of Naples Federico II, Via Cinthia 4, 80126 Naples, Italy, Research Center Borstel Leibniz Lung Center, Parkallee 4a, 23845 Borstel, Germany, Department of Agricultural Sciences, University of Naples Federico II, Via Universita 96, 80055 Portici, Naples, Italy, Department of Chemistry, School of Science, Osaka University, 1-1 Osaka University Machikaneyama, Toyonaka, Osaka 560-0043, Japan

Lipopolysaccharides (LPS) are complex amphiphilic macromolecules forming the external leaflet of the outer membrane of Gram-negative bacteria. The LPS glycolipid portion, named Lipid A, is characterized by a disaccharide backbone carrying multiple acyl chains. Some Lipid A bear very-long-chain-fatty-acids (VLCFA), biosynthesized to span the entire lipid membrane profile. The synbiontic Bradyrhizobium BTAi1 strain carries an unique Lipid A specie, named HoLA, in which VLCFA terminus is covalently-bonded to hopanoid, a triterpenoid displaying structural similarity with eukaryotic sterols. Here, we investigate the role of HoLA in regulating self-assembly, microstructure and thermotropicity of lipid membranes composed by 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-1'-rac-glycerol. DLS and SANS indicated the formation of multilamellar aggregates whose size increases when the hopanoid is present in the bilayer. EPR and DSC showed that HoLA induced a more rigid and ordered organization among the lipids in the bilayer, evocative of a mechanical strengthening. Notably, the presence of calcium ions promote an increase of the bilayer thickness and vesicles size, leading to low curvature aggregates. These results highlight the key role of the hopanoid covalently-linked to VLCFA in defining the physico-chemical properties of bacterial envelope, thus offering a robust scientific basis for the interpretation of the biological activity of the considered strain.

lipopolysaccharides, lipid A, liposomes, Gram-negative bacteria, lipids, Bradyrhizobium, bacterial membranes, hopanoid

NCBI PubMed ID: 33799122
Publication DOI: 10.1016/j.jcis.2021.03.072
Journal NLM ID: 43125
Publisher: Orlando, FL: Academic Press
Correspondence: G. Vitiello ; L. Paduano
Institutions: Department of Chemical, Materials and Production Engineering (DICMaPI), University of Naples Federico II, Piazzale V. Tecchio 80, 80125 Naples, Italy, CSGI, Center for Colloid and Surface Science, via della Lastruccia 3, Sesto Fiorentino (FI), Italy, Department of Chemical Sciences, University of Naples Federico II, via Cintia 4, 80126 Naples, Italy, ISIS Facility, Science & Technology Facilities Council, Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX, United Kingdom
Methods: EPR, DLS, SANS, DCS

lipopolysaccharides, lipid A, liposomes, Gram-negative bacteria, lipids, Bradyrhizobium, bacterial membranes, hopanoid