From Proteopediaproteopedia link
Crystal structure of hH-PGDS with water displacing inhibitor
[HPGDS_HUMAN] Bifunctional enzyme which catalyzes both the conversion of PGH2 to PGD2, a prostaglandin involved in smooth muscle contraction/relaxation and a potent inhibitor of platelet aggregation, and the conjugation of glutathione with a wide range of aryl halides and organic isothiocyanates. Also exhibits low glutathione-peroxidase activity towards cumene hydroperoxide.       
Publication Abstract from PubMed
The inhibition of hH-PGDS has been proposed as a potential target for the development of anti-allergic and anti-inflammatory drugs. Herein we describe our investigation of the binding pocket of this important enzyme and our observation that two water molecules bind to our inhibitors and the enzyme. A series of compounds were prepared to the probe the importance of the water molecules in determining the binding affinity of the inhibitors to the enzyme. The study provides insight into the binding requirements for the design of potent hH-PGDS inhibitors.
Investigation of the binding pocket of human hematopoietic prostaglandin (PG) D2 synthase (hH-PGDS): A tale of two waters.,Trujillo JI, Kiefer JR, Huang W, Day JE, Moon J, Jerome GM, Bono CP, Kornmeier CM, Williams ML, Kuhn C, Rennie GR, Wynn TA, Carron CP, Thorarensen A Bioorg Med Chem Lett. 2012 Jun 1;22(11):3795-9. Epub 2012 Apr 13. PMID:22546671
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.