glnA mutations define the structural gene for glutamine synthetase in Aspergillus

Area of Science:

• Biochemistry
• Molecular Biology
• Mycology

Background:

• Glutamine synthetase is a key enzyme in nitrogen assimilation.
• Understanding glutamine auxotrophs aids in elucidating metabolic pathways.
• Aspergillus species are important model organisms in fungal research.

Purpose of the Study:

• To investigate the role of glutamine synthetase (GS) and γ-glutamyl transferase (GGT) in glutamine auxotrophs of Aspergillus.
• To correlate enzyme activity with growth characteristics in mutants lacking L-glutamine.
• To characterize kinetic properties of GS in selected mutants.

Main Methods:

• Assay of glutamine synthetase activity in five allelic glutamine auxotrophs.
• Measurement of γ-glutamyl transferase activity.
• Assessment of fungal growth in the absence of L-glutamine.
• Determination of kinetic parameters (Km for L-glutamate) for glutamine synthetase.

Main Results:

• Glutamine synthetase activity levels directly correlated with the growth ability of the auxotrophic strains in L-glutamine-deficient media.
• γ-glutamyl transferase activity did not show a correlation with either glutamine synthetase levels or growth properties.
• Two mutants exhibited altered Michaelis constants (Km) for L-glutamate in their glutamine synthetase, differing from the wild type.

Conclusions:

• Glutamine synthetase activity is the primary determinant of growth in these Aspergillus glutamine auxotrophs.
• γ-glutamyl transferase appears to play a minor or non-existent role in L-glutamine biosynthesis in these specific mutant strains.
• Mutations can affect the kinetic properties of glutamine synthetase, impacting its substrate affinity for L-glutamate.