Physicochemical characterization and biological activity of a glycoglycerolipid from Mycoplasma fermentans

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Abstract
We report a comprehensive physicochemical characterization of a glycoglycerolipid from Mycoplasma fermentans, MfGl‐II, in relation to its bioactivity and compared this with the respective behaviors of phosphatidylcholine (PC) and a bacterial glycolipid, lipopolysaccharide (LPS) from deep rough mutant Salmonella minnesota strain R595. The β⇆α gel‐to‐liquid crystalline phase transition behavior of the hydrocarbon chains with Tc = 30 °C for MfGl‐II as well as for LPS exhibits high similarity between the two glycolipids. A lipopolysaccharide‐binding protein (LBP)‐mediated incorporation into negatively charged liposomes is observed for both glycolipids. The determination of the supramolecular aggregate structure confirms the existence of a mixed unilamellar/cubic structure for MfGl‐II, similar to that observed for the lipid A moiety of LPS. The biological data clearly show that MfGl‐II is able to induce cytokines such as tumor necrosis factor‐α (TNF‐α) in human mononuclear cells, although to a significantly lower degree than LPS. In contrast, in the Limulus amebocyte lysate test, MfGl‐II is completely inactive, and in the CHO reporter cell line it does not indicate any reactivity with the Toll‐like receptors TLR‐2 and ‐4, in contrast to control lipopeptides and LPS. These data confirm the applicability of our conformational concept of endotoxicity to nonlipid A structures: an amphiphilic molecule with a nonlamellar cubic aggregate structure corresponding to a conical conformation of the single molecules and a sufficiently high negative charge density in the backbone.

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