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. 2017 Dec 19;8:1089. doi: 10.3389/fphys.2017.01089

Figure 2.

Figure 2

Reaction catalysis and proton-translocating sites in TH. (A) Hydride transfer between the proximate NAD(H) and NADP(H) binding sites of domains I and III. Shown is a nucleotide-bound (sticks), trimeric (domain I)2:(domain III) structure of TH from T. thermophilus (PDB: 4J16), with the NADP(H) binding site in domain III (cyan) facing up. Flexible loops involved in ligand binding are indicated. (B) Proton translocation in domain II. Domain II dimerization (from T. thermophilus) is mediated by TM2-TM2 interaction. Displacement of the second subunit is observed by the alignment of the two structures (PDB: 5UNI, blue; 4O93, yellow) solved under different pH conditions. Crystallographically solved water molecules (red balls) and the channel gating histidine residue (His42α2 on TM3, green sphere) are shown inside the proton channel within one subunit of 5UNI. Structures shown represent a view from the cytoplasmic side.