Glycobiology Advance Access originally published online on April 24, 2008
Glycobiology 2008 18(7):502-508; doi:10.1093/glycob/cwn031
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Comparative structural analyses of the 
-glucan and glycogen from Mycobacterium bovis
Département ‘Mécanismes Moléculaires des Infections Mycobactériennes’, Institut de Pharmacologie et Biologie Structurale (UMR 5089), Université Paul Sabatier (Toulouse III) and Centre National de la Recherche Scientifique, 205, route de Narbonne, 31077 Toulouse cedex, France
1 To whom correspondence should be addressed: Tel: (+33)-561-175-568; Fax: (+33)-561-175-580; e-mail: anne.lemassu{at}ipbs.fr
Received on August 24, 2007; revised on April 16, 2008; accepted on April 18, 2008
Pathogenic mycobacteria such as Mycobacterium tuberculosis, the causative agent of tuberculosis, are surrounded by a noncovalently bound capsule, whose major carbohydrate constituent is a glycogen-like 
-glucan. In the present study we compared the structures of the extracellular polysaccharide to that of the ubiquitous intracellular glycogen. The -glucan was isolated from the culture medium of Mycobacterium bovis Bacille Calmette Guérin, the vaccine strain, in which it is released whereas the intracellular glycogen was obtained after the disruption of cells. The two purified polysaccharides were eluted from permeation gel at a similar position but glycogen was less soluble and gave a more opalescent solution in water than -glucan. Combination of gas chromatography-mass spectrometry analysis of partially O-methylated, partially O-acetylated alditols and NMR analysis confirmed that both polysaccharides were composed of 
4--D-Glcp-1 core, substituted at some six positions with short chains. Degradation of polysaccharides with pullulanase, followed by mass spectrometry analysis of the resulting products, also showed that the two polysaccharides do not differ in terms of lengths of branching. Interestingly, application of analytical ultracentrifugation and dynamic light scattering to the mycobacterial -glucan and glycogen and their enzymatic degradative products indicated that the -glucan possessed a higher molecular mass and was more compact than the glycogen from the same species, allowing the formulation of working structural models for the two polysaccharides. Consistent with the models, the -glucan was found to be less accessible to pullulanase, a debranching enzyme, than glycogen.
Key words: capsule / DLS / Mycobacterium tuberculosis / polysaccharide / pullulanase
2 Present address: Sanofi Pasteur, Département recherche, Plateforme Biochimie, 1541 avenue Marcel Merieux, 69280 Marcy l’Etoile, France.