On the regio- and stereospecificity of arachidonic acid peroxidation catalyzed by mammalian 15-lypoxygenases: a combined molecular dynamics and QM/MM study

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. Cause and effect: The peroxidation of arachidonic acid catalyzed by rabbit 15-lipoxygenase-1 is analyzed at the molecular level by means of molecular dynamics and quantum mechanics/molecular mechanics calculations. The key to understanding the high C₁₅/C₁₁ (after hydrogen abstraction from C₁₃) and C₁₂/C₈ (after hydrogen abstraction from C ₁₀) [n+2] regiospecificity for oxygen addition is the presence of steric-shielding residues.