Cytochrome P450 Mediated Metabolic Mechanism Of Arachidonic Acid

Arachidonic acid is the most abundant polyunsaturated omega-6 fatty acid and one of the essential fatty acids in the human body. This fatty acid is an important precursor for many bioactivators, i.e., prostaglandins, thromboxanes, leukotrienes, lipoxin, epoxyeicosatrienoic acids(EETs) and hydroxyeicosatetraenoic acids(HETEs). These arachidonic acid metabolites function as key regulators in lipoprotein metabolism, inflammation response, vessel healing, uncontrolled vascular remodling, platelet activation as well as pathogenesis of coronary artery disease and hypertension.Cytochrome P450 2J2(CYP2J2) is the major enzyme for arachidonic acid metabolism in human intestines. This CYP enzyme shows notable polymorphisms for different individuals. These polymorphisms, especially T143 A and N404 Y, can significantly reduce the CYP2J2 enzyme activity so as to lower the metabolism of arachidonic. To study the CYP2J2-mediated metabolism mechanism for arachidonic acid and the mutation-induced disfunction for CYP2J2, we predicted the three-dimensional structure for human CYP2J2, and constructed a structural model for arachidonic acid metabolism. Structural assessment results showed that our computational models were accurate and reliable.In our computational model, arachidonic acid adopted a U conformation to bind in the active site of CYP2J2. Leu378 and Gly486 formed hydrogen bonds with the carbonyl group of arachidonic acid. These hydrogen bonds could recognize and position arachidonic acid in the active site with a favorable orientation for the further metabolism reactions.The alkyl group of arachidonic acid was stabilized by hydrophobic interactions formed by Ile127 and Met128.T143A mutation was located on the N-terminal of C-helix, which was an important component for the water access channel. In T143 A mutation, the diameter of the water access channel was reduced to be 3.87 ± 1.21 ?, much smaller than a water molecule diameter. In such case, water transfer was strongly weakened, causing the coemption of water molecules in the active site, and further shutting down the proton transfer during the metabolism processes.N404Y mutation was located on the loop near the N-terminal of K' helix. The substitution of tyrosine for asparagine at amino acid position 404 led to a comparatively large and aromatic side-chain. The steric effect of Tyr404 side-chain could further re-position the side-chain of Leu378, making it no longer to form a hydrogen bond with the carboxyl group of arachidonic acid. This alteration would weaken the substrate binding affinity, so as to reduce the substrate specificity of CYP2J2.