Find in Library

The structure of lipid A from lipopolysaccharide (LPS) of <i>Rhodomicrobium vannielii</i> ATCC 17100 (<i>Rv</i>) a phototrophic, budding bacterium was re-investigated using high-resolution mass spectrometry, NMR, and chemical degradation protocols. It was found that the (Glc<i>p</i>N)-disaccharide lipid A backbone was substituted by a Gal<i>p</i>A residue that was connected to C-1 of proximal Glc<i>p</i>N. Some of this Gal<i>p</i>A residue was β-eliminated by alkaline de-acylation, which indicated the possibility of the presence of another so far unidentified substituent at C-4 in non-stoichiometric amounts. One Man<i>p</i> residue substituted C-4′ of distal Glc<i>p</i>N. The lipid A backbone was acylated by 16:0(3-OH) at C-2 of proximal Glc<i>p</i>N, and by 16:0(3-OH), <i>i</i>17:0(3-OH), or 18:0(3-OH) at C-2′ of distal Glc<i>p</i>N. Two acyloxy-acyl moieties that were mainly formed by 14:0(3-<i>O</i>-14:0) and 16:0(3-<i>O</i>-22:1) occupied the distal Glc<i>p</i>N of lipid A. Genes that were possibly involved in the modification of <i>Rv</i> lipid A were compared with bacterial genes of known function. The biological activity was tested at the model of human mononuclear cells (MNC), showing that <i>Rv</i> lipid A alone does not significantly stimulate MNC. At low concentrations of toxic <i>Escherichia coli</i> O111:B4 LPS, pre-incubation with <i>Rv</i> lipid A resulted in a substantial reduction of activity, but, when higher concentrations of <i>E. coli</i> LPS were used, the stimulatory effect was increased.