Aspergillus nidulans AmyG Functions as an Intracellular α-Amylase to Promote α-Glucan Synthesis

Microbiol Spectr. 2021 Dec 22;9(3):e0064421. doi: 10.1128/Spectrum.00644-21. Epub 2021 Nov 10.


α-Glucan is a major cell wall component and a virulence and adhesion factor for fungal cells. However, the biosynthetic pathway of α-glucan was still unclear. α-Glucan was shown to be composed mainly of 1,3-glycosidically linked glucose, with trace amounts of 1,4-glycosidically linked glucose. Besides the α-glucan synthetases, amylase-like proteins were also important for α-glucan synthesis. In our previous work, we showed that Aspergillus nidulans AmyG was an intracellular protein and was crucial for the proper formation of α-glucan. In the present study, we expressed and purified AmyG in an Escherichia coli system. Enzymatic characterization found that AmyG mainly functioned as an α-amylase that degraded starch into maltose. AmyG also showed weak glucanotransferase activity. Most intriguingly, supplementation with maltose in shaken liquid medium could restore the α-glucan content and the phenotypic defect of a ΔamyG strain. These data suggested that AmyG functions mainly as an intracellular α-amylase to provide maltose during α-glucan synthesis in A. nidulans. IMPORTANCE Short α-1,4-glucan was suggested as the primer structure for α-glucan synthesis. However, the exact structure and its source remain elusive. AmyG was essential to promote α-glucan synthesis and had a major impact on the structure of α-glucan in the cell wall. Data presented here revealed that AmyG belongs to the GH13_5 family and showed strong amylase function, digesting starch into maltose. Supplementation with maltose efficiently rescued the phenotypic defect and α-glucan deficiency in an ΔamyG strain but not in an ΔagsB strain. These results provide the first piece of evidence for the primer structure of α-glucan in fungal cells, although it might be specific to A. nidulans.

Keywords: AmyG; Aspergillus nidulans; cell wall; α-amylase; α-glucan.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Aspergillus nidulans / chemistry
  • Aspergillus nidulans / enzymology*
  • Aspergillus nidulans / genetics
  • Aspergillus nidulans / metabolism
  • Cell Wall / chemistry
  • Cell Wall / metabolism
  • Fungal Proteins / chemistry
  • Fungal Proteins / genetics
  • Fungal Proteins / metabolism*
  • Fungi / classification
  • Fungi / enzymology
  • Fungi / genetics
  • Glucans / biosynthesis*
  • Glucans / chemistry
  • Maltose / metabolism
  • Phylogeny
  • Sequence Alignment
  • alpha-Amylases / chemistry
  • alpha-Amylases / genetics
  • alpha-Amylases / metabolism*


  • Fungal Proteins
  • Glucans
  • Maltose
  • alpha-Amylases