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^●.

Bioluminescence is an attractive alternative to fluorescence for live-cell imaging; however, its low intensity has prevented widespread adoption. Specialized microscopes compensate by sacrificing spatial resolution, field of view and dynamic range—constraints imposed by the highest-sensitivity camera to date: the electron-multiplying charge-coupled device. Recently, quanta image sensor (QIS) technology has emerged for low-light imaging. Here, we show that a commercial QIS camera has exceptional sensitivity; however, its sensor dimensions necessitate a microscope designed to maximize its properties. We introduce a Keplerian-telescope-inspired microscope setup that, with the QIS, results in modestly improved signal-to-noise ratios at substantially higher spatial resolution, field of view and dynamic range, relative to the state of the art. The telescopic design also confers modularity, enabling multimodal imaging with epifluorescence. The ‘QIScope’ makes bioluminescence a viable tool for technically challenging live-cell experiments such as monitoring intracellular and extracellular vesicles simultaneously and the dynamics of low-abundance proteins.