Structural features of the O-antigen of Rickettsia typhi, the etiological agent of endemic typhus

Elucidation of the O-specific polysaccharide chain of lipopolysaccharide (LPS) from Rickettsia typhi, the etiological agent of endemic typhus, is described. Structural information was established by a combination of monosaccharide and methylation analyses of the O-chain, and by mass (MS) and nuclear magnetic resonance (NMR) spectrometries of oligosaccharides arised through its hydrofluoric (HF) acid degradation. Based on the combined data from these experiments, two major polymer populations of the O-specific chain have been determined with the following structural features: α-L-QuiNAc-(1→4)-[α-D-Glc-(1→3)-α-L-QuiNAc-(1→4)]n-α-D-Glc-(1→4)-α-D-Glc→, α-D-Glc-(1→3)-α-L-QuiNAc-(1→4)-[α-D-Glc-(1→3)-α-L-QuiNAc-(1→4)]n-α-D-Glc→. The linear backbone is most probably flanked with short side chains of D-GlcNAc-(1→3)-α-L-QuiNAc-(1→3)-D-GlcNAc→ that are attached to it via L-QuiNAc as a branching point. It is suggested that a dimer α-L-QuiNAc-(1→3)-α-D-GlcNAc may represent a common epitope in the O-antigens of Proteus vulgaris OX19 and R. typhi responsible for the observed serological cross-reactivity.