Identification and characterization of β-d-galactofuranosidases from Aspergillus nidulans and Aspergillus fumigatus

• Published in: Journal of bioscience and bioengineering 2021-01, Vol.131 (1), p.1-7
• Main Authors: Matsunaga, Emiko, Tanaka, Yutaka, Toyota, Saki, Yamada, Hisae, Oka, Takuji, Higuchi, Yujiro, Takegawa, Kaoru
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Aspergillus fumigatus; Aspergillus fumigatus - enzymology; Aspergillus fumigatus - genetics; Aspergillus nidulans - enzymology; Aspergillus nidulans - genetics; Aspergillusnidulans; Galactose - metabolism; Glycoside Hydrolases - chemistry; Glycoside Hydrolases - genetics; Glycoside Hydrolases - metabolism; Hydrolysis; Oligosaccharides - metabolism; Phylogeny; Substrate Specificity; α-l-Arabinofuranose; α-l-Arabinofuranosidase; β-d-Galactofuranose; β-d-Galactofuranosidase
• ISSN: 1389-1723; 1347-4421
• DOI: 10.1016/j.jbiosc.2020.09.006

Although β-d-galactofuranosidases (Galf-ases) that hydrolyze β-d-galactofuranose (Galf)-containing oligosaccharides have been characterized in various organisms, to date no Galf-specific Galf-ase-encoding genes have been reported in Aspergillus fungi. Based on the amino acid sequences of previously identified bacterial Galf-ases, here we found two candidate Galf-specific Galf-ase genes AN2395 (gfgA) and AN3200 (gfgB) in the genome of Aspergillus nidulans. Indeed, recombinant GfgA and GfgB proteins exhibited Galf-specific Galf-ase activity, but no detectable α-l-arabinofuranosidase (Araf-ase) activity. Phylogenetic analysis of GfgA and GfgB orthologs indicated that there are two types of Aspergillus species: those containing one ortholog each for GfgA and GfgB; and those containing only one ortholog in total, among which Aspergillus fumigatus there is a representative with a single ortholog Galf-ase Afu2g14520. Unlike GfgA and GfgB, the recombinant Afu2g14520 protein showed higher Araf-ase activity than Galf-ase activity. An assay of substrate specificity revealed that although GfgA and GfgB are both exo-type Galf-ases and hydrolyze β-(1,5) and β-(1,6) linkages, GfgA hydrolyzes β-(1,6)-linked Galf-oligosaccharide more effectively as compared with GfgB. Collectively, our findings indicate that Galf-ases in Aspergillus species may have a role in cooperatively degrading Galf-containing oligosaccharides depending on environmental conditions.