Structural elucidation of the exopolysaccharide produced by the mangrove fungus Penicillium solitum

A water soluble extracellular polysaccharide, designated GW-12, was obtained from the liquid culture broth of the mangrove fungus Penicillium solitum by ethanol precipitation, anion-exchange and size-exclusion chromatography. Reversed-phase high performance liquid chromatography analysis showed that GW-12 mainly consisted of d-mannose, and its molecular weight was estimated to be about 11.3 kDa determined by high performance gel permeation chromatography. On the basis of chemical and spectroscopic analyses, including methylation analysis and nuclear magnetic resonance (NMR) spectroscopy, the structure of GW-12 may be represented as a mannan with branches. The main chain of GW-12 was composed of (1→2)-linked α-d-mannopyranose and (1→6)-linked α-d-mannopyranose residues, branched by single α-d-mannopyranose units attached to the main chain at C-6 positions of (1→2)-linked α-d-mannopyranose residues. There was three branch points for every seven sugar residues in the backbone.