STRUCTURES OF THE GLYCOPEPTIDOLIPID ANTIGENS OF MYCOBACTERIUM-ABSCESSUS AND MYCOBACTERIUM-CHELONAE AND POSSIBLE CHEMICAL BASIS OF THE SEROLOGICAL CROSS-REACTIONS IN THE MYCOBACTERIUM-FORTUITUM COMPLEX

Mycobacterium abscessus and Mycobacterium chelonae, two members of the Mycobacterium fortuitum complex, contain five major glycolipids. A co mbination of NMR spectroscopy, fast atom bombardment mass spectrometry and chemical degradation was used to elucidate their structures. All the compounds belong to the family of glycopeptidolipids. A 6-deoxy-al pha-L-talosyl unit, which may bear one or two acetyl groups, invariabl y occupies the site of glycosylation on the threonine residue in the v arious compounds. A 3,4-di-O-methyl- or 2,3,4-tri-O-methyl-alpha-L-rha mnosyl unit modifies the alaninol end of the diglycosylated molecules. Both species also contain a multiglycosylated compound consisting of alpha-L-rhamnosyl-(1 --> 2)-3,4-di-O-methyl-alpha-L-rhamnosyl linked t o alaninol, which belongs to the class of new variants of glycopeptido lipids recently described. Using an ELISA, the latter glycolipid as we ll as the diglycosylated ones (not previously reported to be antigenic ), were shown to react with the serum raised against the whole lipid a ntigens of M. chelonae. A comparative serologic study of the native an d chemically modified glycopeptidolipid antigens allowed the identific ation of their epitope as the 3,4-di-O-methyl-alpha-L-rhamnosyl residu e. Similar experiments conducted on the glycopeptidolipids isolated fr om the serologically cross-reacting species M. peregrinum led to the c onclusion that the epitope identified in M. chelonae and M. abscessus was involved in the cross-reactions and demonstrated the existence of a second haptenic moiety in the glycolipids of M. peregrinum, the 3-O- methyl-alpha-L-rhamnosyl unit. In addition to this latter non-shared e pitope, the recently described sulfated glycopeptidolipid antigen of M . peregrinum did not react with the M. chelonae serum, thus further ex plaining the difference in the seroreactivity within the complex.