Endotoxin-like properties of a rhamnolipid exotoxin from Burkholderia (Pseudomonas) plantarii: immune cell stimulation and biophysical characterization.
Here we report on the purification, structural characterization, and biological activity of a glycolipid, 2-O-alpha-L-rhamnopyranosyl-alpha-L-rhamnopyranosyl-alpha(R)-3-hydroxytetradecanoyl-(R)-3-hydroxytetradecanoate (RL-2,2(14)) produced by Burkholderia (Pseudomonas) plantarii. RL-2,2(14) is structurally very similar to a rhamnolipid exotoxin from Pseudomonas aeruginosa and identical to the rhamnolipid of Burkholderia pseudomallei, the causative agent of melioidosis. Interestingly, RL-2,2(14) exhibits strong stimulatory activity on human mononuclear cells to produce tumor necrosis factor alpha, the overproduction of which is known to cause sepsis and the septic shock syndrome. Such a property has not been noted so far for rhamnolipid exotoxins, only for bacterial endotoxins (lipopolysaccharide, LPS). Consequently, we analyzed RL-2,2(14) with respect to its pathophysiological activities as a heat-stable extracellular toxin. Like LPS, the cell-stimulating activity of the rhamnolipid could be inhibited by incubation with polymyxin B. However, immune cell activation by RL-2,2(14) does nor occur via receptors that are involved in LPS (TLR4) or lipopeptide signaling (TLR2). Despite its completely different chemical structure, RL-2,2(14) exhibits a variety of endotoxin-related physicochemical characteristics, such as a cubic-inverted supramolecular structure. These data are in good agreement with our conformational concept of endotoxicity: intercalation of naturally originating virulence factors into the immune cell membrane leads to strong mechanical stress on integral proteins, eventually causing cell activation.
Andrä
Jörg
J
Forschungszentrum Borstel, Leibniz-Zentrum for Medizin und Biowissenschaften, Parkallee 10, D-23845 Borstel, Germany. jandrae@fz-borstel.de
Rademann
Jörg
J
Howe
Jörg
J
Koch
Michel H J
MH
Heine
Holger
H
Zähringer
Ulrich
U
Brandenburg
Klaus
K
D001427:Bacterial Toxins / Q000737:chemistry / Q000302:isolation & purification*; D016957:Burkholderia pseudomallei / Q000737:chemistry*; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D004731:Endotoxins / Q000633:toxicity*; D006017:Glycolipids / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology; D006801:Humans; D007962:Leukocytes / Q000378:metabolism*; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008070:Lipopolysaccharides / Q000276:immunology; D008074:Lipoproteins / Q000276:immunology; D008213:Lymphocyte Activation / Q000187:drug effects*; D011112:Polymyxin B / Q000494:pharmacology; D011550:Pseudomonas aeruginosa / Q000737:chemistry; D013696:Temperature; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
C510849:2-O-alpha-L-rhamnopyranosyl-alpha-L-rhamnopyranosyl-alpha(R)-3-hydroxytetradecanoyl-(R)-3-hydroxytetradecanoate; D001427:Bacterial Toxins; D004731:Endotoxins; D006017:Glycolipids; D008070:Lipopolysaccharides; D008074:Lipoproteins; D014409:Tumor Necrosis Factor-alpha; C418382:rhamnolipid; D011112:Polymyxin B