Glycobiology Advance Access originally published online on March 10, 2005
Glycobiology 2005 15(7):677-686; doi:10.1093/glycob/cwi052
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Structural elucidation of the predominant motifs of the major cell wall arabinogalactan antigens from the borderline species Tsukamurella paurometabolum and Mycobacterium fallax
2 Département "Mécanismes Moléculaires des Infections Mycobactériennes", Institut de Pharmacologie et Biologie Structurale, UMR 5089 du Centre National de la Recherche Scientifique et de l’Université Paul Sabatier, 205 route de Narbonne, 31077 Toulouse cedex 04, France; and 3 Institut Pasteur, 25 rue du Docteur Roux, 75724 Paris cedex 15, France
1 To whom correspondence should be addressed; e-mail: mamadou.daffe{at}ipbs.fr
Received on December 2, 2004; revised on February 28, 2005; accepted on March 3, 2005
Tsukamurella paurometabolum and Mycobacterium fallax are members of the suprageneric actinomycete group Corynebacterineae that possesses a cell wall skeleton composed of a peptidoglycan to which an arabinogalactan is covalently attached. This polysaccharide is further modified by esterification with C60–C80 mycolic acid residues in mycobacteria and T. paurometabolum. However, M. fallax and T. paurometabolum produce polyenoic (up to six double bonds) mycolic acids whereas the most common type of mycobacterial mycolates, called 
-mycolates, are mono- and di-enoic or -cyclopropanated mycolic acids. To determine whether this difference also applied to the structures of cell wall arabinogalactans, competitive inhibition experiments using antibodies raised against the cell wall from Mycobacterium bovis and the arabinogalactans from T. paurometabolum and M. fallax were performed. They demonstrated the structural identity between the polysaccharide of M. fallax and those of mycobacteria and showed a strong similarity between the latter polysaccharides and that of T. paurometabolum. Structural analyses of the per-O-alkylated alditol fragments derived from the polysaccharides by gas chromatography–mass spectrometry (GC-MS) and 13C nuclear magnetic resonance (NMR) spectroscopy of the intact solubilized polysaccharides demonstrated that the polysaccharides from the two species analyzed contained all the major structural features previously characterized in mycobacterial arabinogalactans. These include (1) the homogalactan of alterning 5-linked galactofuranosyl (Galf) and 6-linked Galf residues, (2) a linear 5-linked arabino furanosyl (Araf), (3) a ß-Araf-(1
2)--Araf disaccharide branched on both position 3 and position 5 of an -Araf unit, and (4) a 5-linked--Araf unit branched on both position 3 and position 5 of an -Araf residue. The polysaccharide from T. paurometabolum possesses additional structural domains composed of a terminal (t) Araf directly linked to either a 5-linked--Araf or to both position 3 and position 5 of a 3,5-linked -Araf unit. Both the remarkable similarity of arabinogalactans from Corynebacterineae and their genus- and/or species-specificities are reflected in their 13C NMR spectra that may be used as a valuable help in the identification of members of the actinomycete group.
Key words: arabinogalactan / cell wall / Mycobacterium / Tsukamurella