Beyond Autoxidation and Lipoxygenases: Fatty Acid Oxidation Products in Plant Oils

For decades, research on oxidation of linoleic acid (LA, C18:2 n6) and α-linolenic acid (ALA, C18:3 n3) in plant oils has focused on autoxidatively formed and lipoxygenase-derived 9-hydro(pero)xy- and 13-hydro(pero)xy-LA and -ALA. Here, using a non-targeted approach, we show that other hydroxy fatty acids are more abundant in plant oils. Liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry analyses unveiled highly abundant peaks in flaxseed and rapeseed oils. Using authentic reference standards, seven of the peaks were identified as 9-, 10-, 12-, 13-, and 15-HODE as well as 9- and 13-HOTrE. Additionally, six peaks were characterized based on the retention time, the exact mass of the [M-H]- ion, and its fragment ions as 16-OH-C18:3, 18-OH-C18:3, three isomers of 12-OH-C18:2, and one of 15-OH-C18:2. 16-OH-C18:3 and 18-OH-C18:3 were tentatively identified as 16-OH-ALA and 18-OH-ALA, respectively, based on autoxidation and terminal hydroxylation of ALA using CYP4F2. Investigation of formation pathways suggests that fatty acid desaturase 3 is involved in the formation of the 12-OH-C18:2 isomers, 15-HODE, and its isomer. The dominantly occurring 12-OH-C18:2 isomer was identified as 12R,S-OH-9Z,15Z-octadecadienoic acid (densipolic acid) based on a synthetic standard. The characterized oxylipins occurred in cold-pressed flaxseed and rapeseed oils at concentrations of up to 0.1 g/100 g and thus about sixfold higher than the well-known 9-hydro(pero)xy- and 13-hydro(pero)xy-LA and -ALA. Concentrations in sunflower oil were lower but increased when oil was pressed from preheated seeds. Overall, this study provides fundamental new information about the occurrence of oxidized fatty acids in plant oils, having the potential to characterize their quality and authenticity.

Structure-based evolution of a promiscuous inhibitor to a selective stabilizer of protein-protein interactions

The systematic stabilization of protein–protein interactions (PPI) has great potential as innovative drug discovery strategy to target novel and hard-to-drug protein classes. The current lack of chemical starting points and focused screening opportunities limits the identification of small molecule stabilizers that engage two proteins simultaneously. Starting from our previously described virtual screening strategy to identify inhibitors of 14-3-3 proteins, we report a conceptual molecular docking approach providing concrete entries for discovery and rational optimization of stabilizers for the interaction of 14-3-3 with the carbohydrate-response element-binding protein (ChREBP). X-ray crystallography reveals a distinct difference in the binding modes between weak and general inhibitors of 14-3-3 complexes and a specific, potent stabilizer of the 14-3-3/ChREBP complex. Structure-guided stabilizer optimization results in selective, up to 26-fold enhancement of the 14-3-3/ChREBP interaction. This study demonstrates the potential of rational design approaches for the development of selective PPI stabilizers starting from weak, promiscuous PPI inhibitors.

Small molecule stabilizers of protein–protein interactions hold great therapeutic potential. Based on virtual screening and molecular docking, the authors here develop a strategy to evolve weak, promiscuous inhibitors of 14-3-3 interactions into selective stabilizers of the 14-3-3/ChREBP complex.