Structural and biochemical characterization of the exopolysaccharide deacetylase Agd3 required for Aspergillus fumigatus biofilm formation.
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ABSTRACT:
SUBMITTER: Bamford NC
PROVIDER: S-EPMC7229062 | biostudies-literature | 2020 May
REPOSITORIES: biostudies-literature
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Structural and biochemical characterization of the exopolysaccharide deacetylase Agd3 required for Aspergillus fumigatus biofilm formation.
Bamford Natalie C NC Le Mauff François F Van Loon Jaime C JC Ostapska Hanna H Snarr Brendan D BD Zhang Yongzhen Y Kitova Elena N EN Klassen John S JS Codée Jeroen D C JDC Sheppard Donald C DC Howell P Lynne PL
Nature communications 20200515 1
The exopolysaccharide galactosaminogalactan (GAG) is an important virulence factor of the fungal pathogen Aspergillus fumigatus. Deletion of a gene encoding a putative deacetylase, Agd3, leads to defects in GAG deacetylation, biofilm formation, and virulence. Here, we show that Agd3 deacetylates GAG in a metal-dependent manner, and is the founding member of carbohydrate esterase family CE18. The active site is formed by four catalytic motifs that are essential for activity. The structure of Agd3 ...[more]
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Project description:The exopolysaccharide galactosaminogalactan (GAG) plays an important role in mediating adhesion, biofilm formation, and virulence in the pathogenic fungus Aspergillus fumigatus. Previous work showed that in A. fumigatus, the Lim domain-binding protein PtaB can form a complex with the sequence-specific transcription factor SomA for regulating GAG biosynthesis, biofilm formation, and asexual development. However, transcriptional coactivators required for biofilm formation in A. fumigatus remain uncharacterized. In this study, Spt20, an orthologue of the subunit of the Saccharomyces cerevisiae transcriptional coactivator Spt-Ada-Gcn5-acetyltransferase (SAGA) complex, was identified as a regulator of biofilm formation and asexual development in A. fumigatus. The loss of spt20 caused severe defects in the GAG biosynthesis, biofilm formation, conidiation, and virulence of A. fumigatus. RNA sequence data demonstrated that Spt20 positively regulates the expression of the GAG biosynthesis genes uge3 and agd3, the developmental regulator medA, and genes involved in the conidiation pathway. Moreover, more than 10 subunits of the SAGA complex (known from yeast) could be immunoprecipitated with Spt20, suggesting that Spt20 acts as a structural subunit of the SAGA complex. Furthermore, distinct modules of SAGA regulate GAG biosynthesis, biofilm formation, and asexual development in A. fumigatus to various degrees. In summary, the novel biofilm regulator Spt20 is reported, which plays a crucial role in the regulation of fungal asexual development, GAG biosynthesis, and virulence in A. fumigatus. These findings expand knowledge on the regulatory circuits of the SAGA complex relevant for the biofilm formation and asexual development of A. fumigatus. IMPORTANCE Eukaryotic transcription is regulated by a large number of proteins, ranging from sequence-specific DNA-binding factors to transcriptional coactivators (chromatin regulators and the general transcription machinery) and their regulators. Previous research indicated that the sequence-specific complex SomA/PtaB regulates the biofilm formation and asexual development of Aspergillus fumigatus. However, transcriptional coactivators working with sequence-specific transcription factors to regulate A. fumigatus biofilm formation remain uncharacterized. In this study, Spt20, an orthologue of the subunit of the Saccharomyces cerevisiae Spt-Ada-Gcn5-acetyltransferase (SAGA) complex, was identified as a novel regulator of biofilm formation and asexual development in A. fumigatus. The loss of spt20 caused severe defects in galactosaminogalactan (GAG) production, conidiation, and virulence. Moreover, nearly all modules of the SAGA complex were required for the biofilm formation and asexual development of A. fumigatus. These results establish the SAGA complex as a transcriptional coactivator required for the biofilm formation and asexual development of A. fumigatus.
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Project description:BackgroundAspergillus fumigatus R1 produced xylanase under submerged fermentation which degrades the complex hemicelluloses contained in agricultural substrates. Xylanases have gained considerable attention because of their tremendous applications in industries. The purpose of our study was to purify xylanase and study its biochemical properties. We have predicted the secondary structure of purified xylanase and evaluated its active site residues and substrate binding sites based on the global and local structural similarity.ResultsVarious microorganisms were isolated from Puducherry soil and screened by Congo-red test. The best isolate was identified to be Aspergillus fumigatus R1. The production kinetics showed the highest xylanase production (208 IU/ml) by this organism in 96 h using 1 % rice bran as the only carbon source. The purification of extracellular xylanase was carried out by fractional ammonium sulphate precipitation (30-55 %), followed by extensive dialysis and Bio-Gel P-60 Gel-filtration chromatography. The enzyme was purified 58.10 folds with a specific activity of 38196.22 IU/mg. The biochemical characterization of the pure enzyme was carried out for its optimum pH and temperature (5.0 and 50(0)C), pH and temperature stability, molecular mass (Mr) (24.5 kDa) and pI (6.29). The complete sequence of protein was obtained by mass spectrometry analysis. Apparent Km and Vmax values of the xylanase for birchwood xylan were 11.66 mg/ml and 87.6 μmol min(-1) mg(-1) respectively.ConclusionPurified xylanase was analyzed by mass-spectrometry which revealed 2 unique peptides. Xylanase under current study showed significant production using agricultural residues and a broad range of pH stability in the alkaline region. Xylanase produced by Aspergillus fumigatus R1 could serve as the enzyme of choice in industries.
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Project description:The opportunistic fungus Aspergillus fumigatus causes a set of diseases ranging from allergy to lethal invasive mycosis. Within the human airways, A. fumigatus is embedded in a biofilm that forms not only a barrier against the host immune defense system, but also creates a physical barrier protecting the fungi from chemicals such as antifungal drugs. Novel therapeutic strategies aim at combining drugs that inhibit biofilm synthesis or disrupt existing biofilm with classical antimicrobials. One of the major constituents of A. fumigatus biofilm is the polysaccharide galactosaminogalactan (GAG) composed of α1,4-linked N-acetylgalactosamine, galactosamine, and galactose residues. GAG is synthesized on the cytosolic face of the plasma membrane and is extruded in the extracellular space, where it is partially deacetylated. The deacetylase Agd3 that mediates this last step is essential for the biofilm formation and full virulence of the fungus. In this work, a previously described enzyme-linked lectin assay, based on the adhesion of deacetylated GAG to negatively charged plates and quantification with biotinylated soybean agglutinin was adapted to screen microbial natural compounds, as well as compounds identified in in silico screening of drug libraries. Actinomycin X2, actinomycin D, rifaximin, and imatinib were shown to inhibit Agd3 activity in vitro. At a concentration of 100 µM, actinomycin D and imatinib showed a clear reduction in the biofilm biomass without affecting the fungal growth. Finally, imatinib reduced the virulence of A. fumigatus in a Galleria mellonella infection model in an Agd3-dependent manner.
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