Molecular Organization of the Alkali-insoluble Fraction ofAspergillus fumigatus Cell Wall

Abstract

Physical and biological properties of the fungal cell wall are determined by the composition and arrangement of the structural polysaccharides. Cell wall polymers of fungi are classically divided into two groups depending on their solubility in hot alkali. We have analyzed the alkali-insoluble fraction 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 gel filtration, affinity chromatography with immobilized lectins, and high performance liquid chromatography, several fractions that contained specific interpolysaccharide covalent linkages were isolated. Unique features of the A. fumigatus cell wall are (i) the absence of beta-1,6-glucan and (ii) the presence of a linear beta-1, 3/1,4-glucan, never previously described in fungi. Galactomannan, chitin, and beta-1,3-glucan were also found in the alkali-insoluble fraction. The beta-1,3-glucan is a branched polymer with 4% of 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 side 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 branching 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, galactomannan, and the linear beta-1,3/1,4-glucan.

Genomic sequence of the pathogenic and allergenic filamentous fungus Aspergillus fumigatus

“…The A. fumigatus cell wall is composed of a fibrillar branched b1,3-glucan core bound to chitin, galactomannan and b1,3-1,4-glucan, embedded in an amorphous cement composed of a1,3-glucan, galactomannan and polygalactosamine 22 . b1,6-glucan and peptidomannan, both present in yeast cell walls, are missing in A. fumigatus.…”

Paracoccidioides brasiliensis: chemical and molecular tools for research on cell walls, antifungals, diagnosis, taxonomy

“…While b-1,3-glucan and chitin are recurrent cell wall polysaccharides in the Kingdom Fungi [9], a-1,3-glucan is a rather infrequent occurrence. Besides P. brasiliensis, it has been reported in Schizosaccharomyces pombe [16], Aspergillus nidulans [17], Aspergillus niger [18], Aspergillus fumigatus [19], Cryptococcus neoformans [20], Histoplasma capsulatum [21], and Blastomyces dermatitidis [22], among a few others. A partial chemical structure was reported long ago in P. brasiliensis a-1,3-glucan [14].…”

Clinical significance of non‐Candida fungal blood isolation in patients undergoing high‐risk allogeneic hematopoietic stem cell transplantation (1993–2001)

“…The current criteria, which are far from satisfactory, suggest probable systemic mycoses; they include 1) an immunologically susceptible host (severe granulocytopenia, cellular immune dysfunction, or both), 2) breakthrough fungal infections in patients receiving subtherapeutic antifungals as prophylaxis, and 3) radiographic and clinical features consistent with fungal tissue invasion and tissue damage. 2,18 Detection of fungal antigens, such as galactomannan or D-glucan, in patients' sera may provide important adjuvant information regarding the source of Aspergillus or non-Aspergillus filamentous mold in blood culture samples [22][23][24][25] ; however, nondetectable antigenemia in patients receiving prophylactic or empiric antifungal therapy, such as itraconazole and amphotericin B, may cause serum antigen levels to go undetected and to be misconstrued as (false-) negative results. 26 Serial detection of fungusspecific molecular markers by nucleic acid hybridization and amplification techniques in the host's blood, in bronchioalveolar lavage sample, or in samples from other infected sites may serve as an important adjuvant tool in determining clinically significant fungemia.…”

“…27 These methods also may improve the ability of clinicians to make informed, evidence-based decisions when considering treatment options for immunosuppressed cancer patients or stem cell transplantation recipients with positive blood cultures for a non-Candida fungal species. 28,29 Detection of fungal cell wall components 22 as well as organism-specific and classspecific nucleic acid amplification assays 30 appears promising in diagnosis of clinically significant fungemia and pseudofungemia. We recognize that a critical evaluation of the new and old diagnostic laboratory tests is needed to establish a comprehensive protocol that can be applied with relative ease in hospitalized patients to improve the accuracy of antemortem diagnoses of invasive fungal infections.…”