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Figure 3
Cryo-EM analysis of the active NmqNOR dimer. (a) 2D class averages of dimeric NmqNOR particles in multiple orientations after particle polishing, prior to the final 3D refinement (box size of 200 pixels). (b) 3D reconstruction from cryo-EM filtered and coloured by local resolution (as estimated in RELION-3.0), with the core of the structure being valued at ∼3 Å (as indicated by the colour key at the bottom). (c) NmqNOR dimeric model after structure refinement and model building docked into the sharpened cryo-EM-derived map (grey outline). Chains are coloured as purple and cyan cartoons, respectively. Yellow lines mark the lipid bilayer and subsequently the periplasmic (Peri′) and cytoplasmic (Cyt′) sides. The red dashed line indicates the location of TMII. (d) The dimer interface of NmqNOR is mediated by TMII (purple and cyan helices) of each monomer. Val237, Leu240, Leu241 and Ile244 (map contoured at 7σ) are likely to stabilize the dimeric form of NmqNOR.

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