The Structure of Nitric Oxide Synthase Oxygenase Domain and Inhibitor Complexes

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Abstract
The nitric oxide synthase oxygenase domain (NOS ox ) oxidizes arginine to synthesize the cellular signal and defensive cytotoxin nitric oxide (NO). Crystal structures determined for cytokine-inducible NOS ox reveal an unusual fold and heme environment for stabilization of activated oxygen intermediates key for catalysis. A winged β sheet engenders a curved α-β domain resembling a baseball catcher's mitt with heme clasped in the palm. The location of exposed hydrophobic residues and the results of mutational analysis place the dimer interface adjacent to the heme-binding pocket. Juxtaposed hydrophobic O 2 - and polar l -arginine–binding sites occupied by imidazole and aminoguanidine, respectively, provide a template for designing dual-function inhibitors and imply substrate-assisted catalysis.