The structures of the lipid a moieties from the lipopolysaccharides of two phytopathogenic bacteria, Xanthomonas campestris pv. pruni and Xanthomonas fragariae

Lipopolysaccharides (LPSs) are vital and exclusive structural components of the outer membranes of all Gram-negative bacteria. They play an important role in the communication between the pathogen and both animal and vegetal host cells. Structurally, they comprise in their smooth (S) form three regions, namely the O-specific polysaccharide (or O-antigen), the core region and the lipid A (the endotoxic active moiety). In this paper, the structure of the lipid A moieties from two lipopolysaccharides of two phytopathogenic bacteria, X. campestris pv. pruni and Xanthomonas fragariae, is described. The sugar backbone is constituted by the typical bis(phosphorylated)beta-(1'-->6)-linked D-glucosamine disaccharide. Both lipid A fractions are remarkably heterogeneous with respect to the fatty acid chain length. The major species are hexacylated lipid A, with a symmetric [3+3] distribution in which the secondary fatty acids are exclusively ester-linked. The primary structure of these two complex glycolipids is herein elucidated by means of chemical degradation, MS spectrometry and 2D NMR spectroscopy. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).