Comprehensive genomic analysis of cell wall genes in Aspergillus nidulans

Knowledge of the mechanisms underlying cell wall biosynthesis in Aspergillus spp. is of high relevance to medicine and food safety, and for biotechnological applications. The cell wall of Aspergillus nidulans is composed of galactomannoproteins, 1,3-α-glucan, β-glucans, and chitin. Here, we present a comprehensive inventory of the cell wall-related genes in A. nidulans. This includes glycan-synthetic and glycan-processing enzymes, spore wall maturation enzymes, GPI-anchor processing enzymes, GPI proteins and hydrophobins, and signaling proteins of the cell wall integrity pathway. All major known fungal cell wall-related genes are represented, except for Pir-CWPs. Importantly, we have identified a gene product that is possibly involved in the synthesis of 1,3/1,4-β-glucan, and we propose that four predicted GPI proteins, a mixed-linked β-glucanase and three amylase-like α-glucanases, may have transglucosidic activities pertaining to the processing of 1,3/1,4-β-glucan and 1,3/1,4-α-glucan, respectively. We further present an updated survey of putative GPI proteins. Finally, we present mass spectrometric evidence suggesting the presence of at least twelve covalently-linked cell wall proteins in the hyphal wall of A. nidulans, including ten predicted GPI proteins, most of which belong to carbohydrate-active enzyme families that are also found in the walls of ascomycetous yeasts.