Abstract
Differential amino acid reactivity with chemical probes can provide valuable information on the functionality and ligandability of proteins in native biological systems. Here, we present a quantitative, multiplexed chemical proteomic protocol for in-depth reactivity and ligandability profiling of cysteines in proteins in quiescent and stimulated T cells. This protocol illuminates dynamic immune state-dependent alterations in cysteine reactivity, revealing chemoselective and stereoselective small-molecule interactions with cysteines in structurally and functionally diverse proteins that lack chemical probes. For complete details on the use and execution of this protocol, please refer to Vinogradova et al. (2020).