α-galf 1→6-α-mannopyranoside side chains in Paracoccidioides brasiliensis cell wall are shared by members of the Onygenales, but not by galactomannans of other fungal genera

The water-soluble polysaccharide fraction of the cell wall alkali extract (F1SS) from the mycelial phase of the dimorphic fungus Paracoccidioides brasiliensis is compared with F1SS polysaccharides obtained from the Onygenalean mycelial fungi Ascocalvatia alveolata, Onygena equina and Aphanoascus terreus. These polymers were exclusively composed of mannose and galactose. Data from methylation and NMR analyses reveal that F1SS polysaccharides from the four fungi contain the same residues although in different proportions: [→2,6)-α-D-Manp-(1→]; [2)-α-D-Manp-(1→]; [→6)-α-D-Manp-(1→]; and [α-D-Galf-(1→]. In P. brasiliensis, the repeating unit of the polysaccharide consists of a backbone of [(1→6)-α-D-Manp] substituted at the O-2 position by the disaccharide [α-D-Galf-(1→6)-α-D-Manp-(1→], while the remaining O-2 positions are substituted by single residues of mannose or short chains of (1→2)-mannose. The other species had a lower proportion of galactofuranose-containing side chains and higher proportion of mannose-containing side chains. The similarities found among the F1SS polysaccharides from P. brasiliensis and the Onygenalean A. alveolata, A. terreus and O. equina, reveal the close relatedness of all these fungi, show differences with polysaccharides from other fungal genera and agree with the molecular evidence provided in the scientific literature for the placement of P. brasiliensis within the Onygenales.