Fig. 5: Glutamate-binding site comparison and glutamine feedback inhibition.

a–d Glutamate binding site in a BsGS-SOX/Mg²⁺/ADP (red, 4LNI), (b) MtGS-2OG/Mg²⁺/ATP (cyan), (c) MtGS apo (cyan), and (d) MsGS-Mg²⁺/ATP (purple). Models are in cartoons with ligands and equivalent residues binding SOX as balls and sticks. Oxygen, nitrogen, sulfur, phosphorus, and magnesium are colored red, blue, dark yellow, orange, and green, respectively. Carbons are colored by chain and ATP carbons in yellow. Hydrogen bonds are visualized as black dashes. The Asp-50’ loop region is highlighted by a blue glow. For MsGS, the Tyr-loop is highlighted with an orange glow. An underlined label highlights the catalytic arginine (e.g., R321 in MtGS). e Alignment of the residues involved in glutamate binding (based on BsGS). Side chain and main chain interactions are highlighted by a blue and green box, respectively. A star highlights the arginine responsible for glutamine feedback inhibition in BsGS. f Specific activity in the absence and presence of glutamine in both archaeal GS. Data is represented as mean ± s.d and individual values are shown as white circles (n = 3).