Hematopoietic prostaglandin (PG) D synthase (H-PGDS) is responsible for the production of PGD2 as an allergy or inflammation mediator in mast and Th2 cells. We determined the X-ray structure of human H-PGDS complexed with an inhibitor, 2-(2'-benzothiazolyl)-5-styryl-3-(4'-phthalhydrazidyl) tetrazolium chloride (BSPT) at 1.9 Å resolution in the presence of Mg2+. The styryl group of the inhibitor penetrated to the bottom of the active site cleft, and the tetrazole ring was stabilized by the stacking interaction with Trp 104, inducing large movement around the α 5-helix, which caused the space group of the complex crystal to change from P21 to P1 upon binding of BSPT. The phthalhydrazidyl group of BSPT exhibited steric hindrance due to the cofactor, glutathione (GSH), increasing the IC50 value of BSPT for human H-PGDS from 36.2 μM to 98.1 μM upon binding of Mg2+, because the Km value of GSH for human H-PGDS was decreased from 0.60 μM in the presence of EDTA to 0.14 μM in the presence of Mg2+. We have to avoid steric hindrance of the GSH molecule that was stabilized by intracellular Mg2+ in the mM range in the cytosol for further development of structure-based anti-allergic drugs.
The Japanese Biochemical Society