Ligand and Target Discovery by Fragment-Based Screening in Human Cells

Advances in the synthesis and screening of small-molecule libraries have accelerated the discovery of chemical probes for studying biological processes. Still, only a small fraction of the human proteome has chemical ligands, and the full complement of proteins with potential to be targeted by small molecules remains unknown. Here, we describe a platform that marries fragment-based ligand discovery with quantitative chemical proteomics to map thousands of reversible small molecule-protein interactions directly in human cells, many of which can be site-specifically determined. We advance this knowledge to create ligands that affect the activity of proteins heretofore lacking chemical probes and to identify by phenotypic screening small molecules that promote adipocyte differentiation by engaging the poorly characterized membrane protein PGRMC2. Fragment-based screening in human cells thus provides an extensive proteome-wide map of protein ligandability and facilitates the coordinated discovery of bioactive small molecules and their molecular targets. Overall design: PolyA+ Rnaseq profilling of 3T3-L1 stably overexpressing Gfp or PGRMC2 treated with dmso and induced to differentiate into adipocytes. RNA samples were collected 24 hours after induction of differentiation.