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

•Lipid A and O-antigen structures from P. entomophila was determined.•The lipid A resembles that from other Pseudomonas.•Lipid A has low inflammatory activity.•O-antigen is novel and has a tetrasaccharide repeating unit.•Only 6-deoxy-2acetamido l-sugars compose the O-chain.

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)-α-l-FucNAc-(1→4)-α-l-FucNAc-(1→3)-α-l-FucNAc-(1→3)-β-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.

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