Crystal structures of cyanide complexes of P450cam and the oxygenase domain of inducible nitric oxide synthase—structural models of the short-lived oxygen complexes

The crystal structure of the ternary cyanide complex of P450cam and camphor was determined to 1.8 Å resolution and found to be identical with the structure of the active oxygen complex [I. Schlichting et al., 2000, Science 287, 1615]. Notably, cyanide binds in a bent mode and induces the active conformation that is characterized by the presence of two water molecules and a flip of the carbonyl of the conserved Asp251. The structure of the ternary complex of cyanide, l-arginine, and the oxygenase domain of inducible nitric oxide synthase was determined to 2.4 Å resolution. Cyanide binds essentially linearly, interacts with l-Arg, and induces the binding of a water molecule at the active site. This water is positioned by backbone interactions, located 2.8 Å from the nitrogen atom of cyanide, and could provide a proton required for O–O bond scission in the hydroxylation reaction of nitric oxide synthase.