Figure 1. Af-GlnK3 and its physiological role in ammonium uptake.

A) Top view of the trimer Af-GlnK3, highlighting the ligand binding sites between the monomers and the protruding T-loops that are required for blocking ammonium transport. B) As discussed previously [1], [33], ammonium is actively taken up by Amt proteins and used to aminate glutamate in the ATP-dependent reaction of glutamine synthetase (GS). This reaction is coupled to glutamate∶oxoglutarate amidotransferase (GOGAT) that forms two molecules of glutamate from glutamine and 2-oxoglutarate.