Chemoproteomics identifies protein ligands for monoacylglycerol lipids

Signaling lipids are important hormone-like biomolecules that regulate many physiological processes in humans. However, a significant number of them still remain poorly characterized, despite their direct association to human diseases. While the signaling pathways regulated by the endocannabinoid 2-arachidonoyl-glycerol in mammals are extensively characterized, the same cannot be said about other members of the monoacylglycerol (MAG) family of signaling lipids. Here, we report the synthesis of a bifunctional MAG probe, containing a photoreactive group and an alkyne handle. Using established chemoproteomics approaches coupled to bioorthogonal chemistry, we profile this bifunctional MAG probe in mouse brain and mammalian cell proteomes, and identify hitherto unknown protein ligands for MAG lipids. Finally, we find that the neuronal calcium sensor Hippocalcin is indeed a putative MAG protein ligand, and show that MAG lipids may have a role to play in calcium sensing and downstream signaling in the mammalian brain.