Fig. 1.

Cartoon representation of the assembled NrtABCD nitrate transporter. NrtA is tethered to the periplasmic membrane by a flexible linker and captures nitrate/nitrite in the periplasm for delivery to the transmembrane complex created by NrtB. In many ABC transporters, the transmembrane pore is created by a dimer of two transmembrane spanning polypeptides. NrtC and NrtD are ATPases that couple ATP hydrolysis to nitrate/nitrite transport through the pore. NrtC is unique in that it contains a C-terminal solute-binding domain homologous to NrtA.