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Article

Crystal Structure of Human Prostaglandin F Synthase (AKR1C3)^†^,^‡

Junichi Komoto,^§ Taro Yamada,^§ Kikuko Watanabe, and Fusao Takusagawa*^§

Department of Molecular Biosciences, University of Kansas, 1200 Sunnyside Avenue, Lawrence, Kansas 66045-7534, and Division of Applied Life Science, Graduate School of Integrated Science and Art, University of East Asia, 2-1 Ichinomiya-gakuencho, Shimonoseki, Yamaguchi 751-0807, Japan

Biochemistry, 2004, 43 (8), pp 2188–2198

DOI: 10.1021/bi036046x

Publication Date (Web): February 7, 2004

†

This work has been supported by Grant GM37233 (F.T.) from the National Institutes of Health. Use of the Argonne National Laboratory Structural Biology Center beamline at the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Energy Research, under contract W-31-109-ENG-38.

‡

The atomic coordinates and structure factors have been deposited with the Brookhaven Protein Data Bank as entries 1RY0 and 1RY8.

University of Kansas.

University of East Asia.

To whom correspondence should be addressed: Department of Molecular Biosciences, 3004 Haworth Hall, University of Kansas, 1200 Sunnyside Ave., Lawrence, KS 66045-7534. Telephone: (785) 864-4727. E-mail: xraymain@ku.edu.

Abstract

Prostaglandin H₂ (PGH₂) formed from arachidonic acid is an unstable intermediate and is efficiently converted into more stable arachidonate metabolites (PGD₂, PGE₂, and PGF₂) by the action of three groups of enzymes. Prostaglandin F synthase (PGFS) was first purified from bovine lung and catalyzes the formation of 9α,11β-PGF₂ from PGD₂ and PGF₂_α from PGH₂ in the presence of NADPH. Human PGFS is 3α-hydroxysteroid dehydrogenase (3α-HSD) type II and has PGFS activity and 3α-HSD activity. Human lung PGFS has been crystallized with the cofactor NADP⁺ and the substrate PGD₂, and with the cofactor NADPH and the inhibitor rutin. These complex structures have been determined at 1.69 Å resolution. PGFS has an (α/β)₈ barrel structure. The cofactor and substrate or inhibitor bind in a cavity at the C-terminal end of the barrel. The cofactor binds deeply in the cavity and has extensive interactions with PGFS through hydrogen bonds, whereas the substrate (PGD₂) is located above the bound cofactor and has little interaction with PGFS. Despite being largely structurally different from PGD₂, rutin is located at the same site of PGD₂, and its catechol and rhamnose moieties are involved in hydrogen bonds with PGFS. The catalytic site of PGFS contains the conserved Y55 and H117 residues. The carbonyl O₁₁ of PGD₂ and the hydroxyl O₁₃ of rutin are involved in hydrogen bonds with Y55 and H117. The cyclopentane ring of PGD₂ and the phenyl ring of rutin face the re-side of the nicotinamide ring of the cofactor. On the basis of the catalytic geometry, a direct hydride transfer from NADPH to PGD₂ would be a reasonable catalytic mechanism. The hydride transfer is facilitated by protonation of carbonyl O₁₁ of PGD₂ from either H117 (at low pH) or Y55 (at high pH). Since the substrate binding cavity of PGFS is relatively large in comparison with those of AKR1C1 and AKR1C2, PGFS (AKR1C3) could catalyze the reduction and/or oxidation reactions of various compounds over a relatively wide pH range.