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Category: Clinical Microbiology; Fungi and Fungal Pathogenesis
Cell Wall of Aspergillus fumigatus: a Dynamic Structure, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815523/9781555814380_Chap14-1.gif /docserver/preview/fulltext/10.1128/9781555815523/9781555814380_Chap14-2.gifAbstract:
The cell wall is an essential extracellular organelle that accounts for 20 to 40% of the cellular dry weight of most fungi. Due to the pathogenicity of Aspergillus fumigatus, cell wall composition and chemical organization have been studied to identify fungal molecules involved in host-pathogen interactions, resistance to microbial killing mechanisms, and immune defenses. Polysaccharide composition of the A. fumigatus mycelium and conidial cell wall are listed in this chapter. The alkali-soluble fraction of cell wall polysaccharides is mainly composed of α-1,3-glucan. The majority of antigenic proteins are secreted proteins transiently found in the cell wall before they are secreted in the extracellular environment. A thin layer of regularly arranged rodlets covers the surface of aerial fungal conidia. The number of genes encoding α-1,3-glucan synthases and the essentiality of each individual gene vary according to the fungal species. Analysis of the common domains among the eight chitin synthases of A. fumigatus has shown two clusters of three and four genes and a singleton which are associated with chitin synthesis. The fungal cell wall of A. fumigatus is a complex organization of macromolecules resulting from several biosynthetic pathways: protein synthesis in the endoplasmic reticulum (ER), biosynthesis of mannan and glycans in the ER and Golgi complex, and synthesis of homopolysaccharide at the plasma membrane. Molecular biology methods and biochemical approaches have allowed researchers to identify genes and proteins involved in polysaccharide synthesis.
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Cell cycle of A. fumigatus. Transmission electron micrographs show resting conidia, swelling conidia, and a germ tube of A. fumigatus.
Schematic representation of alkali-insoluble and alkali-soluble polymers of the mycelial cell wall of A. fumigatus.
Structure of the repeating unit of the galactomannan produced by A. fumigatus (Latgé et al., 1994).
Schematic melanin biosynthetic pathway in A. fumigatus (modified from Tsai et al., 1998, 1999, 2001; Langfelder et al., 2003). YWA1, heptaketide naphthopyrone; 1,3,6,8-THN, 1,3,6,8-tetrahydronaphtalene; 1,3,8-THN, 1,3,8-trihydronaphthalene; 1,8-DHN, 1,8-dihydronaphthalene; [O], oxidation step.
Temporal events in the biosynthesis of the structural β-1,3-glucan-chitin core. For simplification, only glucan synthase is represented, but chitin synthase is active at the same time and at the same location as glucan synthase. Linear chains of glucan are modified by both branching and cross-linking enzymes.
Polysaccharidic composition of the A. fumigatus mycelium and conidial cell wall a
Enzymes associated with synthesis of the mycelium and conidial cell wall in A. fumigatus