N C N C Ca 2 + D97 D93 D96 Y8 GSH α 2 α 1 α 7 α 3 α 4 α 6 α 8 α 9 α 5 β 2 β 4 β 3 β 1 Medicines can help people suppress the feelings of he ad ac he s or pe ri od pa in s. Bu t at th e sa me ti me , t h e r e a r e s i d e e f f e c t s . S o m e t i m e s p e o p l e f e e l s l e e p y w h e n t h e y u s e m e d i c i n e . M e d i c i n e c o n t a i n i n g a s p i r i n o r i n d o m e t a s i n e i n h i b i t s cyc loo xyg ene se (CO X) tha t cat aly zes the rea cti on fr om ar ac hi do ni c ac id to pr os ta gl an di n ( PG ) H 2 in the arachidonic acid cascade ( Fig. 1 ). PGH 2 is the starting compound which is utilized to obtain other t y p e s o f p r o s t a g l a n d i n , P G D 2 , P G F 2 α a n d P G E 2 , and so on. Each PG has a specific function in the t i s s u e c o n c e r n e d . P G D 2 i n t h e b r a i n h a s t h e f u n c t i o n o f p r o m o t i n g s l e e p , h o w e v e r , i n o t h e r t i s s u e s , P G D 2 i s p r o d u c e d f r o m m a s t c e l l s a s a n allergic mediator or inflammatory mediator. PGF 2 α was the first compound to be discovered which has the role of contracting the oviductal smooth muscle. PGE 2 has the role of regulating body temperature and also promotes wakening. The inhibition of the p r o d u c t i o n o f P G H 2 b y m e d i c i n e c a u s e s s i d e Structure of Prostaglandin D Synthase Complexed with Drug Molecules F i g . 1 . B i o s y n t h e t i c P a t h w a y o f P r o s t a g l a n d i n s ( PGs ) with compositional formulas and their roles. The difference of each PG is the stereochemistry of hydroxyl group or functional group. H-PGDS absolutely requires glutathione ( GSH ) f o r s t e r e o s p e c i f i c i s o m e r z a t i o n f r o m P G H 2 t o PGD 2 . We determined the X-ray structures of the na ti ve an d su bs tr at e an al og co mp le xe s of hu ma n H-PGDS with glutathione ( GSH ) in the presence of Ca 2 + or Mg 2 + . The metal binding site was found at t h e d i m e r i n t e r f a c e w h e r e s i x a s p a r t a t e s , A r g 1 4 and GSH construct a large hydrogen bond network regulated by metal ions ( Fig. 2 ). Ca 2 + reduces the K m value for substrate, while, Mg 2 + reduces the K m v a l u e f o r G S H a s w e l l a s t h e s u b s t r a t e . M g 2 + shows a remarkable change in the hydrogen bond e f f e c t s d u e t o t h e l a c k o f s p e c i f i c p r o s t a n o i d s i n various tissues. Each prostaglandin is formed by a s p e c i f i c e n z y m e , P G D s y n t h a s e , P G F s y n t h a s e and PGE synthase, respectively. As for the design o f a n t i - a l l e r g i c d r u g s , t h e s t r u c t u r e o f h u m a n hematopoietic PGD synthase ( H-PGDS ) is the most p o t e n t t a r g e t , a s d e m o n s t r a t e d i n a n a l l e r g i c asthma model with prostaglandin D receptor gene- d i s r u p t e d m i c e [ 1 ] , a n d a s a l s o d e m o n s t r a t e d b y t r a n s g e n i c m i c e t h a t o v e r p r o d u c e P G D 2 , t h u s exacerbating asthmatic reactions [2]. Fig. 2. The whole structure and the metal binding site of human H-PGDS. The metal b i n d i n g s i t e w a s f o u n d a t t h e d i m e r interface where six aspartates exist. COOH PGH 2 COOH O O OH PGE 2 OH COOH O HO PGD 2 COOH HO OH O PGF sy nthase Anti-allergic Drug Target PGD synthase Inhibited by aspirin Arachidonic acid PGE synthase PGF 2 α α Regulates body temperature Contraction of the oviductal smooth muscle Allergic and inflammatory mediator HO HO OH COOH 16 K112 R14 GSH K198 W39 Y8 (c) C K112 R14 GSH K198 Q36 Q109 W39 (a) K112 R14 GSH K198 Q36 Q109 W39 (b) (c) (a) (b) Base - GSH Attack by GSH & Product release H N NH 3 + S O O - O - O O O N H O H HO HO HO O C R14 R14 recognizes the ω -chain HO O C O O HO O O H N S O - NH 3 + + H 3 N - O N H O - O HN NH R14 ω -chain GSH Insertion of ω -chain & Rotation of R14 O S - HN NH 3 + NH NH 3 + - H N O - O O H N O O O - O O O OH O C HO Ca 2+ O CH 2 OH HO O C 1 3 4 6 8 1 0 2 5 7 9 11 1 2 13 14 15 16 17 18 19 20 Epoxymethano PGF ( U44 ) Methanoepoxy PGF ( U46 ) OH HO O C 1 3 4 6 8 1 0 2 5 7 9 11 1 2 13 14 15 16 17 18 19 20 H 2 C O ne tw or k, pr om ot in g a fr ee ro ta ti on of Arg14, which results in a low K m v a l u e f o r G S H . T h e C a 2 + - a n d M g 2 + - b o u n d c o m p l e x s t r u c t u r e s with two kinds of substrate analogs p r o v i d e s n a p s h o t s o f s u c c e s s i v e binding of the substrate analogs to t h e e n z y m e , i n d i c a t i n g a p o s s i b l e n o v e l r e a c t i o n m e c h a n i s m , regulated by the metal ion, for the i s o m e r i z a t i o n f r o m t h e 9 , 1 1 - e n d p e r o x i d e g r o u p o f P G H 2 t o P G D 2 w i t h t h e 9 - h y d r o x y - 1 1 - k e t o group. Tsuyoshi Inoue a,b (a) Osaka University (b) Japan Science and Technology Corp., PRESTO E-mail: inouet @ chem.eng.osaka-u.ac.jp References [1] T. Matsuoka et al. , Science 287 (2000) 2013. [2] Y. Fujitani et al. , J. Immunol. 168 (2002) 443. [ 3 ] T . I n o u e , N . O k a z a k i , H . S h i s h i t a n i , S . Kinugasa, Y. Okano, H. Matsumura, Y. Kai, M. Ya ma mo to , T. Ku ma sa ka , D. Ir ik ur a, N. U o d o m e , O . H a y a i s h i , a n d Y . U r a d e , i n preparations. F i g . 3 . T w o k i n d s o f s u b s t r a t e a n a l o g s u s e d f o r t h e complex structure analysis. The difference is in only the location of the oxygen atom in the cyclopentane ring. Fig. 4. We obtained three different binding m o t i f s o f t h e s u b s t r a t e a n a l o g s i n t h e presence of Ca 2 + or Mg 2 + , providing X-ray s n a p s h o t s o f t h e s u c c e s s i v e b i n d i n g o f t h e s u b s t r a t e a n a l o g s t o t h e e n z y m e . W e a r e n o w p r o p o s i n g t h e n o v e l r e a c t i o n mechanism on the right side of each figure. K112 D96 R14 GSH K198 W39 Y8 K11 2 D96 R14 GSH K19 8 Q36 Q109 W39 K11 2 D96 R14 GSH K19 8 Q36 Q109 W39 17
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