Determination of the structure of the O-antigen and the lipid A from the entomopathogenic bacterium Pseudomonas entomophila lipopolysaccharide along with its immunological properties

The structure and the immunology of the lipopolysaccharide (LPS) of Pseudomonas entomophila, an entomopathogenic bacterium isolated from the fruit fly Drosophila melanogaster, was characterized. The O-antigen portion was established and resulted to be built up of a repetitive unit constituted by four monosaccharide residues, all L configured, all deoxy at C-6 and with an acetamido function at C-2: ->3)-?-l-FucNAc-(1->4)-?-l-FucNAc-(1->3)-?-l-FucNAc-(1->3)-?-l-QuiNAc-(1-> The structural analysis of lipid A, showed a mixture of different species. The diphosphorylated glucosamine backbone carries six fatty acids consistent with the composition C10:0 3(OH), C12:0 2(OH) and C12:0 3(OH), whereas other species differs by the number of phosphates and/or of fatty acids. The immunology experiments demonstrated that the LPS structure of P. entomophila displayed a low ability to engage the TLR4-mediated signaling correlated to a significant antagonistic activity toward hexa-acylated LPS structures.