title: Structures of prostacyclin synthase and its complexes with substrate analog and inhibitor reveal a ligand-specific heme conformation change.
abstract: Prostacyclin synthase (PGIS) is a cytochrome P450 (P450) enzyme that catalyzes production of prostacyclin from prostaglandin H(2). PGIS is unusual in that it catalyzes an isomerization rather than a monooxygenation, which is typical of P450 enzymes. To understand the structural basis for prostacyclin biosynthesis in greater detail, we have determined the crystal structures of ligand-free, inhibitor (minoxidil)-bound and substrate analog U51605-bound PGIS. These structures demonstrate a stereo-specific substrate binding and suggest features of the enzyme that facilitate isomerization. Unlike most microsomal P450s, where large substrate-induced conformational changes take place at the distal side of the heme, conformational changes in PGIS are observed at the proximal side and in the heme itself. The conserved and extensive heme propionate-protein interactions seen in all other P450s, which are largely absent in the ligand-free PGIS, are recovered upon U51605 binding accompanied by water exclusion from the active site. In contrast, when minoxidil binds, the propionate-protein interactions are not recovered and water molecules are largely retained. These findings suggest that PGIS represents a divergent evolution of the P450 family, in which a heme barrier has evolved to ensure strict binding specificity for prostaglandin H(2), leading to a radical-mediated isomerization with high product fidelity. The U51605-bound structure also provides a view of the substrate entrance and product exit channels.
authors.affiliation: Institute of Biochemistry, College of Life Sciences, National Chung Hsing University, Taichung City 402, Taiwan.
authors.forename: Yi-Ching
authors.initials: YC
authors.lastname: Li
authors.forename: Chia-Wang
authors.initials: CW
authors.lastname: Chiang
authors.forename: Hui-Chun
authors.initials: HC
authors.lastname: Yeh
authors.forename: Pei-Yung
authors.initials: PY
authors.lastname: Hsu
authors.forename: Frank G
authors.initials: FG
authors.lastname: Whitby
authors.forename: Lee-Ho
authors.initials: LH
authors.lastname: Wang
authors.forename: Nei-Li
authors.initials: NL
authors.lastname: Chan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D011464:Epoprostenol / Q000096:biosynthesis; D006418:Heme / Q000737:chemistry; D019746:Intramolecular Oxidoreductases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008024:Ligands; D008914:Minoxidil / Q000494:pharmacology; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011463:Prostaglandins H / Q000378:metabolism; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D013379:Substrate Specificity; D013816:Thermodynamics; D015027:Zebrafish / Q000235:genetics / Q000378:metabolism
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D008024:Ligands; D011463:Prostaglandins H; D011994:Recombinant Proteins; D006418:Heme; D008914:Minoxidil; C015014:azo analog I; D003577:Cytochrome P-450 Enzyme System; D011464:Epoprostenol; D019746:Intramolecular Oxidoreductases; C022461:prostacyclin synthetase