Characterization of a Novel Branched Tetrasaccharide of 3-Deoxy-d-manno-oct-2-ulopyranosonic Acid

For the first time, the tetrasaccharide Kdoalpha2-->5Kdoalpha2-->5(Kdoalpha2-->4)Kdo (Kdo is 3-deoxy-D-manno-oct-2-ulopyranosonic acid) has been identified in a bacterial lipopolysaccharide (LPS), i.e. in the core region of LPS from Acinetobacter baumannii NCTC 10303. The LPS was analyzed using compositional analysis, mass spectrometry, and NMR spectroscopy. The disaccharide D-GlcpNbeta1-->6D-GlcpN, phosphorylated at O-1 and O-4', was identified as the carbohydrate backbone of the lipid A. The Kdo tetrasaccharide is attached to O-6' of this disaccharide and is further substituted by short L-rhamnoglycans of varying length and by the disaccharide D-GlcpNAcalpha1-->4D-GlcpNA (GlcpNA, 2-amino-2-deoxy-glucopyranosuronic acid). The core region is not substituted by phosphate residues and represents a novel core type of bacterial LPS. The complete carbohydrate backbone of the LPS is shown in Structure I as follows: where Rha is rhamnose. Except were indicated, monosaccharides possess the D-configuration. Sugars marked with an asterisk are present in non-stoichiometric amounts.