Structure of the O-antigen of Acinetobacter lwoffii EK30A; identification of d-homoserine, a novel non-sugar component of bacterial polysaccharides.

We established a peculiar structure of the O-specific polysaccharide (O-antigen) of a psychrotrophic strain of Acinetobacter lwoffii, EK30A, isolated from a 1.6-1.8 million-year-old Siberian permafrost subsoil sediment sample. The polysaccharide was released by mild acid degradation of the lipopolysaccharide and studied using chemical analyses, Smith degradation, (1)H and (13)C NMR spectroscopy and mass spectrometry. It was found to contain d-homoserine, which is N-linked to 4-amino-4,6-dideoxy-d-glucose (Qui4N) and is N-acylated itself with acetyl in about half of the repeating units or (S)-3-hydroxybutanoyl group in the other half. The following is the structure of the tetrasaccharide repeating unit of the polysaccharide: -->3)-beta-d-Quip4NAcyl-(1-->6)-alpha-d-Galp-(1-->4)-alpha-d-GalpNAc-(1-->3)-alpha-d-FucpNAc-(1--> where Acyl stands for either N-acetyl- or N-[(S)-3-hydroxybutanoyl]-d-homoseryl.