Structural and immunological properties of the phenolic glycolids from Mycobacterium gastri and Mycobacterium kansasii

Abstract

Mycobacterial species-specific antigens belong to the three following classes: phenolic glycolipids (Phe G1), acyltrehalose-containing lipooligosaccharidesand polar glycopeptidolipids. These antigens have been chemically defined and alkali-labile epitopes were found to characterize the lipooligosaccharide antigen type. In the present study the major Mycobacterium kansasii phenolic glycolipid epitope namely Phe G1 K-I was delineated as the distal monoacetylated disaccharidic residue: 2,6-dideoxy-4-O-methyl-.alpha.-D-arabino-hexopyranosyl-(1 .fwdarw. 3)-2-O-methyl-4-O-acetyl-.alpha.-L-fucopyranose. This acetoxy group is required for K-I epitope recognition demonstrating that alkali-labile epitopes also occur in the phenolic glycolipid antigen class. Using immunoelectron microscopy, the Phe G1 K-I epitope was localized around the electron-transparent layer on the M. kansasii cell-wall surface. Furthermore, two new phenolic glycolipids namely Phe G1 K-III and Phe-G1 K-IV were discovered in minute amounts. They were purified and characterized by their retention time in direct-phase column HPLC. These molecules are also M. kansasii antigens, whose epitopes differ from that of Phe G1 K-I. The complete family of phenolic glycolipids Phe G1 K-I, K-II, K-III and K-IV was found in both rough and smooth variants of both M. kansasii and Mycobacterium gastri species.