Amide utilization in Aspergillus nidulans: evidence for a third amidase enzyme

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Fungal nitrogen metabolism relies on amidase enzymes for nutrient assimilation.
• Aspergillus nidulans utilizes various nitrogen sources, including amides.
• Specific amidases in A. nidulans have been previously characterized.

Purpose of the Study:

• To investigate the genetic basis for the inability of Aspergillus nidulans to utilize certain amides as nitrogen sources.
• To characterize the enzyme affected by the gmdA mutation.
• To elucidate the regulation and substrate specificity of amidase enzymes in A. nidulans.

Main Methods:

• Genetic analysis of A. nidulans mutants.
• Enzyme activity assays for amidase function.
• Biochemical characterization of enzyme properties and regulation.

Main Results:

• A mutation in the gmdA gene leads to the loss of ability to use benzamide, phenylacetamide, and other amides as sole nitrogen sources.
• The gmdA1 lesion results in significantly reduced levels of a general amidase enzyme with broad substrate activity.
• The general amidase is repressed by nitrogenous metabolites like ammonium but not by induction or carbon catabolite repression.
• Evidence suggests the general amidase is distinct from previously known acetamidase and formamidase.
• A fourth amidase activity, capable of hydrolyzing valeramide and hexanamide, was identified.

Conclusions:

• The gmdA gene is essential for the expression of a general amidase in A. nidulans, which is critical for utilizing a wide range of amides.
• The general amidase is subject to regulation by nitrogen metabolites, with ammonium acting as a repressor.
• A. nidulans possesses multiple amidase enzymes with distinct substrate specificities and regulatory mechanisms.