Conversion of human 5-lipoxygenase to a 15-lipoxygenase by a point mutation to mimic phosphorylation at Serine-663

Locating a lipid at the portal to the lipoxygenase active site

Lipoxygenase enzymes initiate diverse signaling pathways by specifically directing oxygen to different carbons of arachidonate and other polyunsaturated acyl chains, but structural origins of this specificity have remained unclear. We therefore determined the nature of the lipoxygenase interaction with the polar-end of a paramagnetic lipid by electron paramagnetic resonance spectroscopy. Distances between selected grid points on soybean seed lipoxygenase-1 (SBL1) and a lysolecithin spin-labeled on choline were measured by pulsed (electron) dipolar spectroscopy. The protein grid was designed by structure-based modeling so that five natural side chains were replaced with spin labels. Pairwise distances in 10 doubly spin-labeled mutants were examined by pulsed dipolar spectroscopy, and a fit to the model was optimized. Finally, experimental distances between the lysolecithin spin and each single spin site on SBL1 were also obtained. With these 15 distances, distance geometry localized the polar-end and the spin of the lysolecithin to the region between the two domains in the SBL1 structure, nearest to E236, K260, Q264, and Q544. Mutation of a nearby residue, E256A, relieved the high pH requirement for enzyme activity of SBL1 and allowed lipid binding at pH 7.2. This general approach could be used to locate other flexible molecules in macromolecular complexes.

Catalytic convergence of manganese and iron lipoxygenases by replacement of a single amino acid

Lipoxygenases (LOXs) contain a hydrophobic substrate channel with the conserved Gly/Ala determinant of regio- and stereospecificity and a conserved Leu residue near the catalytic non-heme iron. Our goal was to study the importance of this region (Gly(332), Leu(336), and Phe(337)) of a lipoxygenase with catalytic manganese (13R-MnLOX). Recombinant 13R-MnLOX oxidizes 18:2n-6 and 18:3n-3 to 13R-, 11(S or R)-, and 9S-hydroperoxy metabolites (∼80-85, 15-20, and 2-3%, respectively) by suprafacial hydrogen abstraction and oxygenation. Replacement of Phe(337) with Ile changed the stereochemistry of the 13-hydroperoxy metabolites of 18:2n-6 and 18:3n-3 (from ∼100% R to 69-74% S) with little effect on regiospecificity. The abstraction of the pro-S hydrogen of 18:2n-6 was retained, suggesting antarafacial hydrogen abstraction and oxygenation. Replacement of Leu(336) with smaller hydrophobic residues (Val, Ala, and Gly) shifted the oxygenation from C-13 toward C-9 with formation of 9S- and 9R-hydroperoxy metabolites of 18:2n-6 and 18:3n-3. Replacement of Gly(332) and Leu(336) with larger hydrophobic residues (G332A and L336F) selectively augmented dehydration of 13R-hydroperoxyoctadeca-9Z,11E,15Z-trienoic acid and increased the oxidation at C-13 of 18:1n-6. We conclude that hydrophobic replacements of Leu(336) can modify the hydroperoxide configurations at C-9 with little effect on the R configuration at C-13 of the 18:2n-6 and 18:3n-3 metabolites. Replacement of Phe(337) with Ile changed the stereospecific oxidation of 18:2n-6 and 18:3n-3 with formation of 13S-hydroperoxides by hydrogen abstraction and oxygenation in analogy with soybean LOX-1.

Emerging roles of eosinophils and eosinophil-derived lipid mediators in the resolution of inflammation

Acute inflammation and its resolution are essential processes for tissue protection and homeostasis. Once thought to be a passive process, the resolution of inflammation is now shown to involve active biochemical programs that enable inflamed tissues to return to homeostasis. The mechanisms by which acute inflammation is resolved are of interest, and research in recent years has uncovered new endogenous anti-inflammatory and pro-resolving lipid mediators (i.e., lipoxins, resolvins, protectin, and maresin) generated from polyunsaturated fatty acids (PUFAs). This review presents new insights into the cellular and molecular mechanisms of inflammatory resolution, especially the roles of eosinophils, and a series of omega-3 PUFA-derived anti-inflammatory lipid mediators that they generate.