Fig. 3.

Structure of the human nNOSox dimer (PDB: 4D1N). Monomers are colored differently for sake of clarity. The left magnified section (red) shows the ZnS₄ motif, with arrows pointing to the cysteines of the first monomer and the central zinc cation depicted in Van der Waals representation. The right magnified section (blue) provides a view of the active site, with the heme moiety in the center, coordinated to Cys⁴²⁰ on one side and dioxygen on the other. Interacting with the heme carboxylates, the pterin BH₄ cofactor forms π-stacking interactions with Trp⁶⁸³. Glu⁵⁹⁷ stabilizes the substrate above the heme moiety, and the aromatic residues Phe⁵⁸⁹ and Trp⁴¹⁴ sandwich the latter to maintain the proper organization of the active site. Trp⁵⁹², presumably involved in the electron transfer from NOSred to NOSox, is located at the bottom of the heme-binding pocket. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)