Extended Data Fig. 3. Crystallography of NXR-ABC.

a, asymmetric unit of the KsNXR-ABC crystal structure (left, in three orientations) compared with interactions present in the tubules (right). The eight KsNXR-ABC heterotrimers in the crystallographic asymmetric unit are shown in different colors; one strand of the double helix making up the asymmetric unit is shown in orange, blue, light blue and red, the other in beige, yellow, purple and green. Each strand consists of the same head-to-tail dimer of heterotrimers (shown in blue and light blue in the topmost orientation shown) that is also observed in the tubules. The strands of the helices in the crystal structure are capped on either side with a further heterotrimer (orange and red in the topmost orientation) that take the position of KsNXR-T in the tubules (top right). b, the locally averaged simulated annealing 2mFo-DFc omit map is shown (beige) as well as the pterins (beige sticks) and molybdenum atom (green sphere) of the final refined KsNXR-ABC structure. The closed proximal pterin of the EBDH structure²⁶ is shown in light green. The density shows that like the distal pterin, the proximal pterin is in the pyran-open state.