Fig. 3: Structural analysis of JtNorQ^WBNorD and functional role of the NorD linker.

a ATPase activities of PdNorQ/D and JtNorQ/D complexes. Numbers given are averages with standard deviation (n = 3). Pd indicates the P. denitrificans enzymes, whereas Jt indicates the enzymes from J. thermophila. WB superscript denotes Walker B mutation, and VWA superscript indicates that the complex was expressed without the NorD N-terminal domain and flexible linker. Source data are provided as a Source Data file. b Cryo-EM structure of JtNorQ^WBNorD at 3.3 Å resolution. The structure is coloured as in Fig. 1. The NorQ protomers are colour-coded in shades of blue according to their position in the spiral, from top (dark) to bottom (light). H2i (helix 2 inserts) are shown in yellow, preS1 (pre-sensor 1) loops in light green, and the tip of the NorD finger is shown in red. c Conformational states refined from the JtNorQ^WBNorD dataset. The proportion of each population in the total dataset is given in %. Major differences are found in the location of the NorD domains. Only models of NorD and NorQ subunits B and E are shown as side view slice (top row) and top view (bottom row). Colour-coding as in Fig. 1 (NorQ coloured in shades of blue according to position in the spiral, NorD^NTD purple with the NorQ subunit it binds to in the different states indicated, NorD^VWA hot pink and the finger red). d Side view slices of state 3 and 4 showing NorD and NorQ subunits C and F. The distances between Cβ atoms of NorD V241 and A393 are indicated as black arrows. e NOR activities and non-haem iron content in the Pd-cNOR from the NorD linker deletion constructs with a schematic overview (using the JtNorQ/D cartoons) to the left. Numbers given are averages with standard deviation (n = 3–4). Source data are provided as a Source Data file.