title: Crystal structure of constitutive endothelial nitric oxide synthase: a paradigm for pterin function involving a novel metal center.
abstract: Nitric oxide, a key signaling molecule, is produced by a family of enzymes collectively called nitric oxide synthases (NOS). Here, we report the crystal structure of the heme domain of endothelial NOS in tetrahydrobiopterin (H4B)-free and -bound forms at 1.95 A and 1.9 A resolution, respectively. In both structures a zinc ion is tetrahedrally coordinated to pairs of symmetry-related cysteine residues at the dimer interface. The phylogenetically conserved Cys-(X)4-Cys motif and its strategic location establish a structural role for the metal center in maintaining the integrity of the H4B-binding site. The unexpected recognition of the substrate, L-arginine, at the H4B site indicates that this site is poised to stabilize a positively charged pterin ring and suggests a model involving a cationic pterin radical in the catalytic cycle.
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine 92697-3900, USA.
authors.forename: C S
authors.initials: CS
authors.lastname: Raman
authors.forename: H
authors.initials: H
authors.lastname: Li
authors.forename: P
authors.initials: P
authors.lastname: Martásek
authors.forename: V
authors.initials: V
authors.lastname: Král
authors.forename: B S
authors.initials: BS
authors.lastname: Masters
authors.forename: T L
authors.initials: TL
authors.lastname: Poulos
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001708:Biopterins / Q000031:analogs & derivatives* / Q000378:metabolism; D002384:Catalysis; D002412:Cations / Q000378:metabolism; D002417:Cattle; D003460:Crystallization; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000378:metabolism; D019281:Dimerization; D006418:Heme / Q000378:metabolism; D006860:Hydrogen Bonding; D008958:Models, Molecular; D018716:Molecular Mimicry; D019001:Nitric Oxide Synthase / Q000737:chemistry* / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III; D017433:Protein Structure, Secondary; D011622:Pterins / Q000378:metabolism*; D016415:Sequence Alignment; D015032:Zinc / Q000378:metabolism*
chemical_list: D002412:Cations; D011622:Pterins; D001708:Biopterins; D006418:Heme; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; C003402:sapropterin; D015032:Zinc; D003545:Cysteine