No^• represses the oxygenation of arachidonoyl pe by 15lox/pebp1: Mechanism and role in ferroptosis

We recently discovered an anti-ferroptotic mechanism inherent to M1 macrophages whereby high levels of NO^• suppressed ferroptosis via inhibition of hydroperoxy-eicosatetraenoyl-phosphatidylethanolamine (HpETE-PE) production by 15-lipoxygenase (15LOX) complexed with PE-binding protein 1 (PEBP1). However, the mechanism of NO^• interference with 15LOX/PEBP1 activity remained unclear. Here, we use a biochemical model of recombinant 15LOX-2 complexed with PEBP1, LC-MS redox lipidomics, and structure-based modeling and simulations to uncover the mechanism through which NO^• suppresses ETE-PE oxidation. Our study reveals that O₂ and NO^• use the same entry pores and channels connecting to 15LOX-2 catalytic site, resulting in a competition for the catalytic site. We identified residues that direct O₂ and NO^• to the catalytic site, as well as those stabilizing the esterified ETE-PE phospholipid tail. The functional significance of these residues is supported by in silico saturation mutagenesis. We detected nitrosylated PE species in a biochemical system consisting of 15LOX-2/PEBP1 and NO^• donor and in RAW264.7 M2 macrophages treated with ferroptosis-inducer RSL3 in the presence of NO^•, in further support of the ability of NO^• to diffuse to, and react at, the 15LOX-2 catalytic site. The results provide first insights into the molecular mechanism of repression of the ferroptotic Hp-ETE-PE production by NO^• .