An Activity-Guided Map of Electrophile-Cysteine Interactions in Primary Human T Cells

Electrophilic compounds originating from nature or chemical synthesis have profound effects on immune cells. These compounds are thought to act by cysteine modification to alter the functions of immune-relevant proteins; however, our understanding of electrophile-sensitive cysteines in the human immune proteome remains limited. Here, we present a global map of cysteines in primary human T cells that are susceptible to covalent modification by electrophilic small molecules. More than 3,000 covalently liganded cysteines were found on functionally and structurally diverse proteins, including many that play fundamental roles in immunology. We further show that electrophilic compounds can impair T cell activation by distinct mechanisms involving the direct functional perturbation and/or degradation of proteins. Our findings reveal a rich content of ligandable cysteines in human T cells and point to electrophilic small molecules as a fertile source for chemical probes and ultimately therapeutics that modulate immunological processes and their associated disorders. [Display omitted] •Chemical proteomics identifies cysteine reactivity changes in activated T cells•Chemical proteomics maps ligandable cysteines in diverse immune-relevant proteins•Cysteine-directed electrophilic compounds suppress T cells by distinct mechanisms•Electrophile-cysteine interactions promote the degradation of immune proteins Integrated chemical proteomics and phenotypic screening furnishes a global portrait of cysteine reactivity and ligandability in primary human T cells and enables the discovery of electrophilic small molecules that suppress T cell activation and promote the degradation of immunomodulatory proteins.