Understanding the Molecular Mechanism of the Ala-versus-Gly Concept Controlling the Product Specificity in Reactions Catalyzed by Lipoxygenases:A Combined Molecular Dynamics and QM/MM Study of Coral 8R-Lipoxygenase
Lipoxygenases
(LOXs) are a family of enzymes that catalyze the
highly specific hydroperoxidation of polyunsaturated fatty acids,
such as arachidonic acid. Different stereo- or/and regioisomer hydroperoxidation
products lead later to different metabolites that exert opposite physiological
effects in the animal body and play a central role in inflammatory
processes. The Gly-Ala switch of a single residue is crucial for the
stereo- and regiocontrol in many lipoxygenases. Herein, we have combined
molecular dynamics simulations with quantum mechanics/molecular mechanics
calculations to study the hydrogen abstraction step and the molecular
oxygen addition step of the hydroperoxidation reaction of arachidonic
acid catalyzed by both wild-type Coral 8<i>R</i>-LOX and
its Gly427Ala mutant. We have obtained a detailed molecular understanding
of this Ala-versus-Gly concept. In wild type, molecular oxygen adds
to C<sub>8</sub> of arachidonic acid with an <i>R</i> stereochemistry.
In the mutant, Ala427 pushes Leu385, blocks the region over C<sub>8</sub>, and opens an oxygen access channel now directed to C<sub>12</sub>, where molecular oxygen is added with an <i>S</i> stereochemistry. Thus, the specificity turns out to be dramatically
inverted. Since Leu385 is highly conserved among many lipoxygenase
isoforms, this mechanism can be general, and we propose that the presence
of such type of bulky and hydrophobic residues can be key in controlling
the extreme regio- and stereospecificity of lipoxygenases and, as
a consequence, their physiological effects