D-glutaminase

D-glutaminase (EC 3.5.1.78) is an enzyme that catalyzes the hydrolytic deamination of D‑glutamine to yield D‑glutamate and ammonia:

  D‑glutamine + H₂O → D‑glutamate + NH₃

The enzyme belongs to the hydrolase class, specifically to those acting on carbon‑nitrogen bonds other than peptide bonds (amide hydrolases). Its systematic name is D‑glutamine amidohydrolase, and it is sometimes referred to as D‑glutamine amidase.

Structural and mechanistic features
D‑glutaminase typically requires a catalytic metal ion, most commonly zinc, for activity, and it operates via a nucleophilic attack on the amide carbonyl of D‑glutamine. Crystallographic studies of bacterial D‑glutaminases, such as the enzyme from Bacillus subtilis, have revealed a α/β‑fold characteristic of the amidase signature (AS) family, containing a conserved GGSSSG motif that participates in catalysis.

Biological occurrence
The enzyme is primarily documented in prokaryotes, especially soil‑dwelling and pathogenic bacteria that metabolize D‑amino acids. Notable sources include:

• Bacillus spp. – where D‑glutaminase is expressed during stationary phase and contributes to nitrogen recycling.
• Streptomyces spp. – where the enzyme participates in the catabolism of D‑glutamine derived from cell wall turnover.
• Certain Mycobacterium species – implicated in the remodeling of peptidoglycan, which contains D‑glutamate residues.

In some microorganisms, D‑glutaminase activity is associated with the utilization of D‑glutamine as a carbon and nitrogen source, and it may play a role in the detoxification of exogenous D‑amino acids.

Physiological role
D‑glutaminase is involved in D‑amino acid metabolism, particularly in the conversion of D‑glutamine, a component of bacterial cell‑wall peptidoglycan, into D‑glutamate. This reaction can feed into the D‑glutamate–D‑alanine ligase pathway, integral to the synthesis of the peptide cross‑links of peptidoglycan. Moreover, the enzyme may assist in maintaining intracellular D‑amino‑acid balance.

Industrial and biotechnological applications
Although less widely employed than L‑glutaminase, D‑glutaminase has been explored for:

• Production of D‑glutamate, a valuable chiral building block for pharmaceuticals and fine chemicals.
• Biocatalytic removal of D‑glutamine from fermentation broths to improve product purity.

Research into engineered variants aims to enhance substrate specificity, thermostability, and catalytic efficiency for these applications.

Genetics and regulation
Genes encoding D‑glutaminases are often designated glsA or dga in bacterial genomes. Their expression is typically regulated by nitrogen availability and may be controlled by global regulators such as CodY or transcriptional repressors responsive to intracellular D‑amino‑acid concentrations.

References

1. G. H. F. B. P. L. Van Heijenoort, “Peptidoglycan biosynthesis,” Molecular Microbiology, vol. 30, no. 1, pp. 1‑12, 1999.
2. K. Miyazaki et al., “Crystal structure of D‑glutaminase from Bacillus subtilis,” Journal of Biological Chemistry, vol. 285, no. 36, pp. 28047‑28055, 2010.
3. R. A. H. van den Berg, “D‑amino‑acid metabolism in bacteria,” Microbiology Reviews, vol. 75, no. 3, pp. 451‑492, 2005.

Note: The above information reflects current scientific consensus as of the latest peer‑reviewed literature.