The Early Asexual Development Regulator fluG Codes for a Putative Bifunctional Enzyme.

Area of Science:

• * Molecular Biology
• * Developmental Biology
• * Biochemistry

Background:

• * FluG is a known regulator of asexual development in *Aspergillus nidulans*, with null mutants exhibiting abnormal growth and lacking conidia.
• * Previous research suggested FluG homology to prokaryotic glutamine synthetase, but its catalytic activity remained unconfirmed.

Purpose of the Study:

• * To perform an in-depth sequence analysis of FluG.
• * To elucidate the specific roles of FluG's functional domains in asexual development.
• * To investigate the catalytic requirements and functional conservation of FluG.

Main Methods:

• * Detailed sequence analysis of the FluG polypeptide.
• * Separate expression and functional assessment of N-terminal and C-terminal regions.
• * Site-directed mutagenesis of key catalytic residues.
• * Heterologous expression of functional domain homologs from other bacterial species.

Main Results:

• * FluG comprises distinct N-terminal amidohydrolase and C-terminal γ-glutamyl ligase regions.
• * The C-terminal region is critical for asexual development; the N-terminal region enhances conidial production under nutrient-rich conditions.
• * Essential catalytic residues were identified in both regions, and their mutation abolished function.
• * Homologous regions from *Lactobacillus paracasei* and *Pseudomonas aeruginosa* partially restored FluG function.

Conclusions:

• * FluG functions as a bifunctional enzyme in *Aspergillus nidulans* development.
• * The enzyme likely participates in a novel metabolic or signaling pathway involving γ-glutamylated intermediates.
• * FluG's functional domains exhibit conservation across different bacterial species.