Physico-chemical analysis of lipid A fractions of lipopolysaccharide from Erwinia carotovora in relation to bioactivity

Highly purified bisphosphoryl, monophosphoryl and dephosphoryl lipids A fro m Erwinia carotovora with different acylation patterns were characterized p hysico-chemically. Applying matrix assisted laser desorption/ionization mas s spectrometry, the purity of the lipid A fractions was determined, and fro m monolayer measurements the molecular space requirement was estimated. Fou rier transform infrared spectroscopy allowed the elucidation of the gel to liquid crystalline phase transition of the acyl chains as well as the deter mination of the tilt angle of the diglucosamine backbone with respect to th e acyl chain direction applying dichroitic measurements with attenuated tot al reflectance. With synchrotron radiation small-angle X-ray diffraction th e supramolecular aggregate structure was determined, and with fluorescence resonance energy transfer spectroscopy the lipopolysaccharide binding prote in induced intercalation of lipid A into a phospholipid matrix correspondin g to that of the macrophage membrane was investigated. From the results, a clear dependence of the physico-chemical parameters on the particular lipid A structure can be followed. Furthermore, these parameters correlate well with the biological activities of the various lipids A as deduced from thei r ability to induce biological activity (Limulus assay and cytokine inducti on in mononuclear cells). These results contribute to a closer interpretati on of the physicochemical prerequisites for endotoxic activity as found for enterobacterial lipid A. (C) 2001 Elsevier Science B.V. All rights reserve d.