Structures of the glycopeptidolipid antigens from serovars in the Mycobacterium avium/Mycobacterium intracellulare/Mycobacterium scrofulaceum serocomplex

Abstract

The 'C-mycosidic' glycopeptidolipid typing antigens from all serovars in the Mycobacterium avium/M. intracellulare/M. scrofulaceum complex have been examined to varying extents. Detailed analysis of those from serovars 8, 9, 16 and 25 show that the antigens consist of short acetylated oligosaccharides linked to a common fattyacyl-peptidyl-O-(3,4-di-O-methylrhamnose) 'core'. The oligosaccharide units, in a form suitable for chemical studies, were liberated as oligosaccharide alditols on treatment of the glycopeptidolipids with alkaline borohydride solution. The alditol in the reduced oligosaccharides from all sources is 6-deoxytalitol. Moreover rhamnose is also always present, indicating that a 'basal' disaccharide, rhamnosyl-6-deoxytalosyl, is always linked to the allo-threonine in the acylpeptide. In addition the oligosaccharides from the glycopeptidolipids of each serovar are distinguished by their own individualistic sugars: 3-O-methylglucose in serovar 8; 2,3-di-O-methylfucose in serovar 9; 2-O-methylfucose in serovar 25; 4-O-methylrhamnose in the oligosaccharide from one of the two glycopeptidolipids in serovar 16 and apparently another rhamnosyl substituent in the other oligosaccharide. The glycopeptidolipid antigens in their structural principals, cellular location and physiological role bear a striking miniscule resemblance to cell wall components of other bacteria such as the O-antigenic and R-antigenic lipopolysaccharides.