Structural analysis of the lipopolysaccharide core of a rough, cystic fibrosis isolate of Pseudomonas aeruginosa

Lipopolysaccharide (LPS) expressed by isolates of Pseudomonas aeruginosa fr om cystic fibrosis patients lacks the O-polysaccharide chain but the degree to which the rest of the molecule changes has not been determined. We anal yzed, for the first time, the core structure of an LPS from a rough, cystic fibrosis isolate of P. aeruginosa. The products of mild acid hydrolysis an d strong alkaline degradation of the LPS were studied by ESI MS, MALDI MS, and NMR spectroscopy. The following structure was determined for the highes t-phosphorylated core-lipid A backbone oligosaccharide isolated after alkal ine deacylation of the LPS: [GRAPHICS] where Kdo and Hep are 3-deoxy-D-manno-octulosonic acid and L-glycero-D-mann o-heptose, respectively; all sugars are in the pyranose form and have the D configuration unless stated otherwise. The outer core region occurs as two isomeric glycoforms differing in the position of rhamnose (Rha). The inner core region carries four phosphorylation sites at two Hep residues, Hep(I) being predominantly bisphosphorylated and Hep(II) monophosphorylated. In t he intact LPS, both Hep residues carry monophosphate and diphosphate groups in nonstoichiometric quantities, GaIN is N-acylated by an L-alanyl group, Hep(II) is 7-O-carbamoylated, and the outer core region is nonstoichiometri cally O-acetylated at four sites. Therefore, the switch to the, LPS-rough p henotype in cystic fibrosis isolates of P. aeruginosa is not accompanied by losses of core monosaccharide, phosphate or acyl components. The exact pos itions of the O-acetyl groups and the role of the previously undescribed O- acetylation in the LPS core of P. aeruginosa remain to be determined.