Candida albicans cell wall comprises a branched β-D-(1→6)-glucan with β-D-(1→3)-side chains

The structure of immunogenic and immunomodulatory cell wall glucans of Candida albicans is commonly interpreted in terms of a basic polysaccharide consisting of a beta-D-(1 -> 3)-linked glucopyranosyl backbone possessing beta-D-(1 -> 6)-linked side chains of varying distribution and length. This proposed molecular architecture has been re-evaluated by the present study on the products of selective enzymolysis of insoluble C albicans glucan particles (GG). High resolution H-1 (400 and 700 MHz) and C-13 (100 and 175 MHz) NMR analyses were performed on a soluble P-glucan preparation (GG-Zym) obtained by GG digestion with endo-beta-D-(1 -> 3)-glucanase and on its high- (Pool 1) and low-molecular weight (Pool 2) sub-fractions. The resonances typical of uniformly beta-D-(1 -> 6)- and beta-D-(1 -> 3)-linked linear glucans, together with additional multiplets assigned to short-chain oligogluco sides, were detected in GG-Zym. Pool 1 (46.3 +/- 6.4% of GG-Zym content) consisted of beta-D-(1 -> 6)-linked glucopyranosyl polymers, with short beta-D-(1 -> 3)-branched side chains of 2.20 +/- 0.02 units (branching degree (DB) = 0. 14 +/- 0.03). Pool 2 was a mixture of glucose and linear short-chain beta-D-(1 -> 3)-oligoglucosides. Further digestion of Pool 1 by beta-D-(1 -> 6)-glucanase yielded a mixture of glucose and short beta-D-(1 -> 6)-linked, either linear or beta-D-(1 -> 3,6) branched, oligomers. These endoglucanase digestion patterns were consistent with the presence in C. albicans cell wall glucans of beta-D-(1 -> 6)-linked glucopyranosyl backbones possessing beta-D-(1 -> 3)-linked side chains, a structure very close to that of beta-D-(1 -> 6)-glucan from Saccharornyces cerevisiae yeast. This finding may provide the grounds for further elucidation of the cell wall structure and a better understanding of the biological properties of C. albicans beta-glucans. (c) 2008 Elsevier Ltd. All rights reserved.