Structure and assembly of epiglucan, the extracellular (1→3; 1→6)-β-glucan produced by the fungus Epicoccum nigrum strain F19

In a previous article [Carbohydr. Res. 2001, 331, 163-171] two different structures for the possible modular repeating unit of the extracellular P-glucan, epiglucan produced by the fungus Epicoccum nigrum strain F19 were proposed. Clarifying which was the more likely one was considered essential before attempts were made to understand how epiglucan was assembled by this fungus. Data from Smith degradation analyses of epiglucan were consistent with the repeating unit of structure I, where single glucosyl residues are attached by (1 -> 6)-beta-linkages to two out of every three glucosyl residues in the (1-3)-beta-linked glucan backbone. Repeated Smith degradations of C-14-glucose labelled epiglucan showed that chain elongation occurred from its non-reducing end. Side chain insertion into the growing glucan was followed by analysis of real time incorporation of C-13-glucose into epiglucan by C-13 NMR, and C-14-glucose by enzymic digestion of the synthesised C-14-epiglucan. All data obtained were consistent with the view that single (1 -> 6)-beta-linked glucosyl side residues are inserted simultaneously as the glucan backbone elongates. [GRAPHICS] (c) 2005 Elsevier Ltd. All rights reserved.