Molecular organization of the alkali-insoluble fraction of Aspergillus fumigatus cell wall

Physical and biological properties of the fungal cell wall are determined b y the composition and arrangement of the structural polysaccharides. Cell w all polymers of fungi are classically divided into two groups depending on their solubility in hot alkali. We have analyaed the alkali-insoluble fract ion of the Aspergillus fumigatus cell wall, which is the fraction believed to be responsible for fungal cell wall rigidity. Using enzymatic digestions with recombinant endo-beta-1,3-glucanase and chitinase, fractionation by g el filtration, affinity chromatography with immobilized lectins, and high p erformance liquid chromatography, Several fractions that contained specific interpolysaccharide covalent linkages were isolated. Unique features of th e A. fumigatus cell wall are (i) the absence of beta-1,6-glucan and (ii) th e presence of a linear beta-1,3/1,4-glucan, never previously described in f ungi. Galactomannan, chitin, and beta-1,3-glucan were also found in the alk ali-insoluble fraction. The beta-1,3-glucan is a branched polymer with 4% o f beta-1,6 branch points. Chitin, galactomannan, and the Linear beta-1,3/1, 4-glucan were covalently linked to the nonreducing end of beta-1,3-glucan s ide chains. As in Saccharomyces cerevisiae, chitin was linked via a beta-1, 4 linkage to beta-1,3-glucan. The data obtained suggested that the branchin g of beta-1,3-glucan is an early event in the construction of the cell wall , resulting in an increase of potential acceptor sites for chitin, galactom annan, and the linear beta-1,3/1,4-glucan.