Amino acid determinants in cyclooxygenase-2 oxygenation of the endocannabinoid 2-arachidonylglycerol

The endocannabinoid, 2-arachiclonylglycerol (2-AG), is an endogenous ligand for the central (CBI) and peripheral (CB2) cannabinoid receptors and has b een shown to be efficiently and selectively oxygenated by cyclooxygenase (C OX)-2. We have investigated 2-AG/COX-2 interactions through site-directed m utagenesis. An evaluation of more than 20 site-directed mutants of murine C OX-2 has allowed for the development of a model of 2-AG binding within the COX-2 active site. Most strikingly, these studies have identified Arg-513 a s a critical determinant in the ability of COX-2 to efficiently generate pr ostaglandin Hz glycerol ester, explaining, in part, the observed isoform se lectivity for this substrate. Mutational analysis of Leu-531, an amino acid located directly across from Arg-513 in the COX-2 active site, suggests th at 2-AG is shifted in the active site away from this hydrophobic residue an d toward Arg-513 relative to arachidonic acid. Despite this difference, asp irin-treated COX-2 oxygenates 2-AG to afford 15-hydroxyeicosatetraenoic aci d glycerol ester in a reaction analogous to the C-15 oxygenation of arachid onic acid observed with acetylated COX-2. Finally, the differences in subst rate binding do not alter the stereospecificity of the cyclooxygenase react ion; 2-AG-derived and arachidonic acid-derived products share identical ste reochemistry.