Activity-based protein profiling in human M2 macrophages using DHA-based photoaffinity probes

17-Hydroxydocosahexaenoic acid (17-HDHA), an oxidative metabolite of the fish oil constituent docosahexaenoic acid (DHA, 22:6 n-3), is a signaling lipid with anti-inflammatory properties. The molecular mechanisms underlying the biological effect of 17-HDHA are poorly understood. Here, we report the design, synthesis and application of a complementary pair of bioorthogonal photoreactive probes based on the polyunsaturated scaffold of 17-HDHA and DHA. In these probes, an alkyne serves as a handle to introduce a fluorescent reporter group or a biotin-affinity tag via copper(I)-catalyzed azide-alkyne cycloaddition. This pair of chemical probes was used to map specific protein interaction partners of 17-HDHA in primary human macrophages, which led to the identification of prostaglandin reductase 1 (PTGR1) as a target of 17-HDHA, but not DHA. Ensuing biochemical studies revealed that PTGR1 converted 17-HDHA into 17-oxo-DHA, which inhibited the biosynthesis of the pro-inflammatory lipids 5-HETE and LTB4 in human macrophages and neutrophils.