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Glycobiology Advance Access published online on April 24, 2008
Glycobiology, doi:10.1093/glycob/cwn031
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© The Author 2008. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Comparative Structural Analyses of the {alpha}-Glucan and Glycogen from Mycobacterium bovis

Premkumar Dinadayala#,*,, Tounkang Sambou*, Mamadou Daffé and Anne Lemassu

Université Paul Sabatier (Toulouse III) and Centre National de la Recherche Scientifique, Institut de Pharmacologie et Biologie Structurale (UMR 5089), Département ‘Mécanismes Moléculaires des Infections Mycobactériennes’, 205, route de Narbonne, 31077 Toulouse cedex (France).

Corresponding author: Tel: (+33) 561 175 568; fax: (+33) 561 175 580; anne.lemassu{at}ipbs.fr

Received on August 24, 2007; accepted on April 18, 2008

Pathogenic mycobacteria such as Mycobacterium tuberculosis, the causative agent of tuberculosis, are surrounded by a non-covalently bound capsule, whose major carbohydrate constituent is a glycogen-like {alpha}-glucan. In the present study we compared the structures of the extracellular polysaccharide to that of the ubiquitous intracellular glycogen. The {alpha}-glucan was isolated from the culture medium of Mycobacterium bovis BCG, the vaccine strain, in which it is released whereas the intracellular glycogen was obtained after 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 {alpha}-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-{alpha}-D-Glcp-1-> core, substituted at some 6 positions with short chains. Degradation of polysaccharides with pullulanase, followed by mass spectrometry analysis of the resulting products also showed that the lengths of the branched chains do not differ from one another polysaccharide. Interestingly, application of analytical ultracentrifugation and dynamic light scattering to the mycobacterial {alpha}-glucan and glycogen and their enzymatic degradative products indicated that the {alpha}-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 {alpha}-glucan was found to be less accessible to pullulanase, a debranching enzyme, than glycogens.

Key words: Mycobacterium, tuberculosis, capsule, DLS / polysaccharide / pullulanase

# Present address: Sanofi Pasteur, Département recherche, Plateforme Biochimie, 1541 avenue Marcel Merieux, 69280 Marcy l’Etoile, France

* These authors contributed equally to this work.


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