gfsA encodes a novel galactofuranosyltransferase involved in biosynthesis of galactofuranose antigen of O ‐glycan in A spergillus nidulans and A spergillus fumigatus

Summary The cells walls of filamentous fungi in the genus A spergillus have galactofuranose ( G al f )‐containing polysaccharides and glycoconjugates, including O ‐glycans, N ‐glycans, fungal‐type galactomannan and glycosylinositolphosphoceramide, which are important for cell wall integrity. Here, we attempted to identify galactofuranosyltransferases that couple G al f monomers onto other wall components in A spergillus nidulans . Using reverse‐genetic and biochemical approaches, we identified that the AN8677 gene encoded a galactofuranosyltransferase, which we called GfsA , involved in G al f antigen biosynthesis. Disruption of gfsA reduced binding of β‐ Gal f ‐specific antibody EB ‐ A 2 to O ‐glycosylated WscA protein and galactomannoproteins. The results of an in‐vitro   G al f antigen synthase assay revealed that GfsA has β1,5‐ or β1,6‐galactofuranosyltransferase activity for O ‐glycans in glycoproteins, uses UDP ‐ d ‐ G al f as a sugar donor, and requires a divalent manganese cation for activity. GfsA was found to be localized at the G olgi apparatus based on cellular fractionation experiments. Δ gfsA cells exhibited an abnormal morphology characterized by poor hyphal extension, hyphal curvature and limited formation of conidia. Several gfsA orthologues were identified in members of the P ezizomycotina subphylum of A scomycota, including the human pathogen A spergillus fumigatus . To our knowledge, this is the first characterization of a fungal β‐galactofuranosyltransferase, which was shown to be involved in G al f antigen biosynthesis of O ‐glycans in the G olgi.