PMID: 21489986

 

    Legend: Sugar

Title : The structural basis of endocannabinoid oxygenation by cyclooxygenase-2

Abstract :

1. The cyclooxygenases ( COX-1 and COX-2 ) oxygenate arachidonic acid (AA) in the committed step of prostaglandin biogenesis
2. Substitutions of I434V, H513R, and I523V constitute the only differences in residues lining the cyclooxygenase channel between COX-1 and COX-2
3. These changes create a hydrophobic pocket in COX-2 , with Arg-513 located at the base of the pocket, which has been exploited in the design of COX-2-selective inhibitors
4. Previous studies have shown that COX-2 , but not COX-1 , can oxygenate endocannabinoid substrates, including 2-arachidonoyl glycerol (2-AG)
5. To investigate the isoform-specific structural basis of endocannabinoid binding to COX-2 , we determined the crystal structure of the 2-AG isomer 1-arachidonoyl glycerol (1-AG) in complex with wild type and R513H murine (mu) COX-2 to 2.2 and 2.35 Å, respectively, and R513H mu COX-2 in complex with AA to 2.45 Å resolution
6. The 2,3-dihydroxypropyl moiety of 1-AG binds near the opening of the cyclooxygenase channel in the space vacated by the movement of the Leu-531 side chain, validating our previous hypothesis implicating the flexibility of the Leu-531 side chain as a determinant for the ability of COX-2 to oxygenate endocannabinoid substrates
7. Functional analyses carried out to compliment our structural findings indicated that Y355F and R513H mu COX-2 constructs had no effect on the oxygenation of 1-AG and 2-AG, whereas substitutions that resulted in a shortened side chain for Leu-531 had only modest effects
8. Both AA and 1-AG bind to R513H mu COX-2 in conformations similar to those observed in the co-crystal structures of these substrates with wild type enzyme