No Laughing Matter: The Unmaking of the Greenhouse Gas Dinitrogen Monoxide by Nitrous Oxide Reductase - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 200

Figure 9 Substrate access and N 2 O binding at the active site of N 2 O reductase. (a) Stereo
representation of the molecular surface at the interface between the cupredoxin domain (blue)
and the ʲ -propeller domain with the active site situated below. Substrate access is provided via a
hydrophic channel along the domain interface, leading to a vestibule close to Cu Z . The access to
the N 2 O binding site on Cu Z is controlled by residues Phe621 and Met627. (b) Observed binding of
N 2 O between Cu A and Cu Z in gas-pressurized crystals of P. stutzeri N 2 OR form I (PDB ID 3SBR).
A difference electron density map for the substrate is shown below a transparent van-der-Waals
surface. Upon N 2 O binding, residue His583 at Cu A was invariably found to coordinate to
the nearby copper ion (Figure 6 ). The positioning of the substrate between the two metal sites
suggests that electron transfer might occur directly from Cu A to N 2 O, rather than involving a
reduction of Cu Z .