Newly found 2-N-acetyl-2,6-dideoxy-beta-glucopyranose containing methyl glucose polysaccharides in M.bovis BCG: revised structure of the mycobacterial methyl glucose lipopolysaccharides.

The specific mycobacterial methyl polysaccharides 3- O -methyl mannose polysaccharide (MMP) and the 6- O -methyl glucose lipopolysaccharides (MGLPs) were shown to modulate the fatty acid biosynthesis by the mycobacterial fatty acid synthetase I (FAS I). This activity is attributed to their fatty acid complexing properties allowing the release of the neo synthesized fatty acyl chain from the enzyme and probably their transport in the cell. To elucidate, at a molecular level, the mechanism of this unusual kind of polysaccharide-lipid biological interaction, we first analyzed, by mass spectrometry and proton nuclear magnetic resonance (1H NMR) spectroscopy, the structure of the polysaccharidic backbone (MGPs) of the MGLPs from Mycobacterium bovis BCG. This work reveals that this strain produces a new kind of MGP containing an unusual monosaccharide never described in the mycobacterial genus: a 2- N -acetyl-2,6-dideoxy-beta-glucopyranosyl. In addition,1H NMR data afforded evidence for the revision of three glycosidic linkages described previously. These modifications affect mainly the reducing end tetrasaccharide and have great consequences on the previously proposed molecular model of the MGP.