Fig. 1. N-Acryloylindole (NAI) as a new chemical tool for Cys profiling and imaging.

a Illustration of the attractive features of NAI. Delocalization of π electrons over NAI increases electrophilicity of the acrylamide warhead, resulting in activation of the acrylamide for fast and complete reaction with nucleophilic Cys, which is not found in other acrylamide compounds such as the negative control N-acryloylindoline (NAine). Together with good selectivity toward Cys, low cellular toxicity, and formation of stable Cys-adduct readily detectable by MS, NAI enables both in vitro and live-cell Cys profiling by gel-based and MS-based chemoproteomic experiments. b Synthetic scheme for N-acryloylindole-alkynes, NAIA-4, and NAIA-5, and negative control compounds, N-acryloylindoline 3a and 3b. c Chemical structures of commonly used cysteine-reactive probes, iodoacetamide-alkyne (IAA) and maleimide-alkyne (MIA), and NAines and NAIAs reported in this study.