Crystal Structure of Nitric Oxide Synthase Bound to Nitro Indazole Reveals a Novel Inactivation Mechanism

• Published in: Biochemistry (Easton) Vol. 40; no. 45; pp. 13448 - 13455
• Main Authors: Raman, C. S, Li, Huiying, Martásek, Pavel, Southan, Garry, Masters, Bettie Sue S, Poulos, Thomas L
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 13.11.2001
• Subjects: Binding Sites; Biopterins - analogs & derivatives; Biopterins - chemistry; Crystallization; Crystallography, X-Ray; Drug Design; Enzyme Inhibitors - chemistry; Enzyme Inhibitors - pharmacology; Indazoles - chemistry; Indazoles - pharmacology; Models, Molecular; Nitric Oxide Synthase - antagonists & inhibitors; Nitric Oxide Synthase - chemistry; Nitroarginine - chemistry; Nitroarginine - pharmacology; Protein Conformation; Substrate Specificity
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi010957u

Nitric oxide is generated under normal and pathophysiological conditions by three distinct isoforms of nitric oxide synthase (NOS). A small-molecule inhibitor of NOS (3-Br-7-nitroindazole, 7-NIBr) is profoundly neuroprotective in mouse models of stroke and Parkinson's disease. We report the crystal structure of the catalytic heme domain of endothelial NOS complexed with 7-NIBr at 1.65 Å resolution. Critical to the binding of 7-NIBr at the substrate site is the adoption by eNOS of an altered conformation, in which a key glutamate residue swings out toward one of the heme propionate groups. Perturbation of the heme propionate ensues and eliminates the cofactor tetrahydrobiopterin−heme interaction. We also present three crystal structures that reveal how alterations at the substrate site facilitate 7-NIBr and structurally dissimilar ligands to occupy the cofactor site.