STRUCTURE OF AN ALPHA-2,6-SIALYLATED LIPOOLIGOSACCHARIDE FROM NEISSERIA-MENINGITIDIS IMMUNOTYPE L1

The recent cloning of the lipooligosaccharide (LOS) alpha-2,3-sialyltr ansferase from Neisseria meningitidis immunotype L3 permitted us to ex amine other immunotypes for this structural gene. We identified the ge ne and measured the enzyme activity in the L1 immunotype strain which had previously been reported to lack sialic acid in its LOS because it contains a terminal alpha-linked galactose which was thought not to b e an acceptor for the sialyltransferase. This finding prompted us to r e-examine the structure of the LOS from the L1 immunotype, which revea led the presence of sialic acid on the terminal alpha-linked galactose . Oligosaccharides derived from the LOS were shown to be sialylated by composition and methylation analysis, mass spectrometry and nuclear m agnetic resonance. The detailed structural analysis showed the sialic acid to occur only at O6 of the terminal alpha-D-galactopyranose resid ue of the alpha-D-Gal-1,4-beta-D-Gal-1,4 -beta-D-glc trisaccharide (P- k epitope) chain of the LOS, in the alpha-D configuration. These data are the first report of a alpha-2,6-linked sialic acid in a bacterial LOS or lipopolysaccharide, and also the first report of a sialylated P -k epitope.