fumigatus, α(1-3) glucan is the major polysaccharide of the cell wall (40% of the cell wall) ( 7). Galactomannan has been shown to be associated with host immune reactions against A. The alkali-soluble (AS) fraction contains mainly α(1-3) glucans and galactomannan ( 1). It is composed of a branched β(1-3) glucan to which are attached chitin, β(1-3) and β(1-4) glucan, and galactomannan ( 7).

The alkali-insoluble (AI) fraction constitutes the wall skeleton. The fungal cell wall of Aspergillus fumigatus is mainly composed of polysaccharides that can be separated into two fractions, depending on their solubility in hot sodium hydroxide ( 7). This result showed that a 50% reduction in the content of the cell wall α(1-3) glucan does not play a significant role in A. Using this model, it was shown that the cell wall and morphogenesis defects of Δags1 and Δags2 were not associated with a reduction in virulence in either mutant. An original experimental model of invasive aspergillosis based on mixed infection and quantitative PCR was developed to analyze the virulence of A. The cellular localization of the two proteins was in agreement with their different functions: Ags1p was localized at the periphery of the cell in connection with the cell wall, whereas Ags2p was intracellularly located. These results showed that Ags1p and Ags2p were functionally different. Only Δags1 presented a reduction in the α(1-3) glucan content of the cell wall. Both Δags mutants have similar altered hyphal morphologies and reduced conidiation levels. fumigatus have an estimated molecular mass of 270 kDa. fumigatus, AGS1 and AGS2, are highly homologous to the AGS genes of Schizosaccharomyces pombe, which encode putative α(1-3) glucan synthases.

In spite of its importance, synthesis of this amorphous polymer has not been investigated to date. Α(1-3) glucan is a main component of the Aspergillus fumigatus cell wall.

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