Membrane protein PurT of 471 aas and 14 TMSs.  In mammals, the concentrative uptake of ascorbic acid (vitamin C) by members of the NAT family is driven by the Na⁺ gradient, while the uptake of nucleobases in bacteria is powered by the H⁺ gradient. The structure of PurC has been determined at 2.80 Å resolution (Weng et al. 2023). PurT_Cp forms a homodimer, and each protomer has 14 transmembrane segments folded into a transport domain (core domain) and a scaffold domain (gate domain). A purine base is present in the structure and defines the location of the substrate binding site. Functional studies reveal that PurT_Cp transports purines but not pyrimidines and that purine binding and transport is dependent on the pH. Mutation of a conserved aspartate residue close to the substrate binding site reveals the critical role of this residue in H⁺-dependent transport of purines. Comparison of the PurT_Cp structure with transporters of the same structural fold suggests that rigid-body motions of the substrate-binding domain are central for substrate translocation across the membrane (Weng et al. 2023).