Table 3.

Predicted role of the catalytic residues from 4LNN (GSI), 4HPP (GGL), and FluG.

Residues			Predicted role
4LNN	4HPP	FluG
D53	V42	S481	Removes a proton from the ammonium ion to create ammonia
E132	E131	E564	Binds Mβ
E134	E133	E566	Binds Mα; susceptible to interact with inhibitors
E189	E180	E626	Binds Mα and the NH3 molecule
E196	E187	E633	Binds Mα
H245	H236	H682	Binds Mβ, via pros nitrogen
N247	H238	H684	Interacts with ATP γ-phosphate
R298	R290	R720	Interacts with the amide group of the glutamate
E304	W296	W726	Abstracts a proton from the transition state to form glutamine and ADP
R316	R308	R739	Polarizes the bound ATP γ-phosphate that forms the γ-glutamyl phosphate
R321	R313	R744	Contacts with the ATP in the transition state
E333	E332	E752	Binds Mβ

Metals labeled as Mα and Mβ correspond to the first and the second Mg²⁺ atoms. Mα and Mβ are located in the first and the second catalytic domain, respectively.