Prostaglandin F2α formation from prostaglandin H2 by prostaglandin F synthase (PGFS): Crystal structure of PGFS containing bimatoprost

Abstract

Prostaglandin H2 (PGH2) formed from arachidonic acid is an unstable intermediate and is efficiently converted into more stable arachidonate metabolites by the action of enzymes. Prostaglandin F synthase (PGFS) has dual catalytic activities: formation of PGF2α from PGH2 by the PGH2 9,11-endoperoxide reductase activity and 9α, 11/β-PGF2 (PGF2αβ) from PGD 2 by the PGD2 11-ketoreductase activity in the presence of NADPH. Bimatoprost (BMP), which is a highly effective ocular hypotensive agent, is a PGF2α analogue that inhibits both the PGD2 11-ketoreductase and PGH2 9,11-endoperoxide reductase activities of PGFS. To examine the catalytic mechanism of PGH2 9,11-endoperoxide reductase, a crystal structure of PGFS[NADPH + BMP] has been determined at 2.0 Å resolution. BMP binds near the PGD2 binding site, but the α and ω-chains of BMP are locate on the ω- and α-chains of PGD2, respectively. Consequently, the bound BMP and PGD 2 direct their opposite faces of the cyclopentane moieties toward the nicotinamide ring of the bound NADP. The α- and ω-chains of BMP are involved in H-bonding with protein residues, while the cyclopentane moiety is surrounded by water molecules and is not directly attached to either the protein or the bound NADPH, indicating that the cyclopentane moiety is movable in the active site. From the complex structure, two model structures of PGFS containing PGF2α and PGH2 were built. On the basis of the model structures and inhibition data, a putative catalytic mechanism of PGH 2 9,11-endoperoxide reductase of PGFS is proposed. Formation of PGF2α from PGH2 most likely involves a direct hydride transfer from the bound NADPH to the endoperoxide of PGH2 without the participation of specific amino acid residues. © 2006 American Chemical Society.