title: Biophysical characterization of synthetic rhamnolipids.
abstract: Synthetic rhamnolipids, derived from a natural diacylated glycolipid, RL-2,2(14), produced by Burkholderia (Pseudomonas) plantarii, were analyzed biophysically. Changes in the chemical structures comprised variations in the length, the stereochemistry and numbers of the lipid chains, numbers of rhamnoses, and the occurrence of charged or neutral groups. As relevant biophysical parameters, the gel (beta) to liquid crystalline (alpha) phase behavior of the acyl chains of the rhamnoses, their three-dimensional supramolecular aggregate structure, and the ability of the compounds to intercalate into phospholipid liposomes in the absence and presence of lipopolysaccharide-binding protein were monitored. Their biological activities were examined as the ability to induce cytokines in human mononuclear cells and to induce chemiluminescence in monocytes. Depending on the particular chemical structures, the physicochemical parameters as well as the biological test systems show large variations. This relates to the acyl chain fluidity, aggregate structure, and intercalation ability, as well as the bioactivity. Most importantly, the data extend our conformational concept of endotoxicity, based on the intercalation of naturally originating amphiphilic virulence factors into membranes from immune cells. This 'endotoxin conformation', produced by amphiphilic molecules with a hydrophilic charged backbone and apolar hydrophobic moiety, and adopting inverted cubic aggregate structures, causes high mechanical stress in target immune cells on integral proteins, eventually leading to cell activation. Furthermore, biologically inactive rhamnolipids with lamellar aggregate structures antagonize the endotoxin-induced activity in a way similar to lipid A-derived antagonists.
authors.affiliation: Forschungszentrum Borstel, Leibniz-Zentrum für Medizin und Biowissenschaften, Borstel, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Howe
authors.forename: Jörg
authors.initials: J
authors.lastname: Bauer
authors.forename: Jörg
authors.initials: J
authors.lastname: Andrä
authors.forename: Andra B
authors.initials: AB
authors.lastname: Schromm
authors.forename: Martin
authors.initials: M
authors.lastname: Ernst
authors.forename: Manfred
authors.initials: M
authors.lastname: Rössle
authors.forename: Ulrich
authors.initials: U
authors.lastname: Zähringer
authors.forename: Jörg
authors.initials: J
authors.lastname: Rademann
authors.forename: Klaus
authors.initials: K
authors.lastname: Brandenburg
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D016207:Cytokines / Q000096:biosynthesis; D031541:Fluorescence Resonance Energy Transfer; D006017:Glycolipids / Q000037:antagonists & inhibitors / Q000138:chemical synthesis* / Q000737:chemistry* / Q000494:pharmacology; D006801:Humans; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism; D007962:Leukocytes / Q000378:metabolism; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D049449:Luminescence; D008954:Models, Biological; D009000:Monocytes / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism; D017550:Spectroscopy, Fourier Transform Infrared; D051195:Toll-Like Receptor 2 / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D016207:Cytokines; D006017:Glycolipids; D051036:Large-Conductance Calcium-Activated Potassium Channels; D018950:Lipopolysaccharide Receptors; D011956:Receptors, Cell Surface; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; C418382:rhamnolipid