An Insight into the Regiospecificity of Linoleic Acid Peroxidation Catalyzed by Mammalian 15-Lipoxygenases

The Journal of Physical Chemistry B (Impact Factor: 3.3). 03/2013; 117(14). DOI: 10.1021/jp312747q
Source: PubMed


15-Lipoxygenases (15-LOs) catalyze the peroxidation reaction of linoleic acid (LA) in mammals producing almost exclusively 13-(S)-hydroperoxyoctadecadienoic acid (13-(S)-HPODE). Although several hypotheses have been formulated, the molecular basis of such enzymatic regiospecificity is unclear. We have here combined quantum mechanics/molecular mechanics (QM/MM) calculations with molecular dynamics simulations to analyze the peroxidation mechanism using a complete rabbit 15-LO-1/LA solvated model. Being equivalent C9 and C13 as for planarity and spin density, the QM/MM potential energy profiles of the O2 addition to those two atoms were calculated. The difference in the potential energy barrier heights is clear enough to justify that O2 selectively attacks C13 giving 13-(S)-HPODE. Oxygenation at C9 is hindered by two steric-shielding residues (Leu597 and Gln548). The calculated free energy profile at 300 K for the O2 addition to C13 confirms that the peroxidation on C13 is a reversible viable process in agreement with experiments. Thus, the subsequent reduction of the peroxyl radical to give the final hydroperoxidated product is expected to give the irreversibility character to the overall process.

Download full-text


Available from: Reynier Suardiaz, Oct 02, 2015
37 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cyclooxygenase (COX) carries out stereospecific oxygen addition to arachidonic acid to generate prostaglandins, plus smaller amounts of 11- and 15-hydroxyeicosatetraenoic acids. For COX-2, the stereochemistry and relative abundance of generated products is influenced by Ser530 acetylation following aspirin treatment. The molecular bases of the high degree of stereospecificity which characterizes COX-2-catalyzed oxygenations are not yet completely understood, nor are the reasons behind the aspirin-induced shift in lipid mediator production. A mechanistic hypothesis is proposed which identifies steric shielding as the main determinant of oxygenation stereospecificity. This hypothesis is supported by a computational model which accurately reproduces experimental oxygenation patterns on both native and aspirin-inhibited COX-2.
    Journal of the American Chemical Society 06/2013; 135(28). DOI:10.1021/ja402870k · 12.11 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 15-Lipoxygenases (15-LOs) catalyse the peroxidation reaction of arachidonic acid (AA) in mammals with remarkable regio- and stereospecificity. This positional-specific peroxidation is of paramount importance because it determines the nature and biological functions of the final metabolites generated by each LO as a result of the oxidative metabolism of AA. Although several hypotheses have been formulated concerning the regio- and stereospecificity of LOs, the molecular basis of such behaviour is still unclear. Herein, we combined quantum mechanics/molecular mechanics calculations with molecular dynamics simulations of the complete rabbit 15-LO/AA solvated model to examine the most accepted hypotheses for the regio- and stereospecificity of LOs. We have found that the clue to explain this specificity is the oxygen-targeting hypothesis through steric shielding of specific residues (mainly Leu597, Gln548 and Phe175, as well as the AA tail itself). Our deductions are based primarily on the analysis of the energy barrier heights from the oxygen addition reaction profiles.
    ChemPhysChem 11/2013; 14(16). DOI:10.1002/cphc.201300629 · 3.42 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We combined quantum mechanics/molecular mechanics calculations with molecular dynamics simulations to study the addition of O2 to the pentadienyl radical of arachidonic acid (AA) catalyzed by the Leu597Val and Leu597Ala mutants of rabbit 15-lipoxygenase (15-rLO). In the Leu597Val mutant, the addition of O2 to C15 of AA is the predominant path, although it reduces the C15/C11 product ratio by almost ten times with respect to the wildtype enzyme. The S stereochemistry is kept. Mutation to Ala causes just the opposite effect: regiospecificity favoring addition to C15 is somewhat sharper than that in the wildtype, but the stereochemistry is R. This is because the extra space created by the mutation to Ala is big enough for AA to move so that it can adopt an alternative binding mode, and this opens new feasible paths for the attack of O2. So, we showed that the Leu597Ala mutant of 15r-LO works as an aspirin-acetylated cyclooxygenase-2, which makes 15-(R)- hydroperoxyeicosatetraenoic acid.
    ChemPhysChem 08/2014; DOI:10.1002/cphc.201402045 · 3.42 Impact Factor