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Figure 2
Monomeric, zinc-bound crystallographic structure of NmqNOR. (a) Monomeric NmqNOR crystal structure with three zinc-binding sites (grey spheres; Zn1, Zn2 and Zn3) and with the periplasmic (Peri′) and cytoplasmic (Cyt′) ends of the lipid bilayer marked with yellow lines. (b) The Zn1 binding site near the proposed proton-entry site at the cytoplasmic end; the 2Fo − Fc density map is shown as a blue mesh, with Zn1 ligated by His257 (contoured at 1.9σ), Glu573 (contoured at 2.4σ), Glu576 (contoured at 3σ) and His577 (contoured at 2σ) (salmon sticks), (c) Zn2 is located close to the binuclear centre (heme b3 and FeB; brown sphere), where it is bound by three conserved glutamates [Glu498 (1.5σ), Glu494 (1σ) and Glu563 (1σ)]. FeB is ligated by only three histidines (His490, His541 and His542; all contoured at 1.5σ), with extra density between the heme b3 iron and nonheme iron modelled as a water (red sphere).

IUCrJ
Volume 7| Part 3| May 2020| Pages 404-415
ISSN: 2052-2525
https://doi.org/10.1107/S2052252520003656