Liganding Functional Tyrosine Sites on Proteins Using Sulfur–Triazole Exchange Chemistry

Tuning
reactivity of sulfur electrophiles is key for advancing
click chemistry and chemical probe discovery. To date, activation
of the sulfur electrophile for protein modification has been ascribed
principally to stabilization of a fluoride leaving group (LG) in covalent
reactions of sulfonyl fluorides and arylfluorosulfates. We recently
introduced sulfur–triazole exchange (SuTEx) chemistry to demonstrate
the triazole as an effective LG for activating nucleophilic substitution
reactions on tyrosine sites of proteins. Here, we probed tunability
of SuTEx for fragment-based ligand discovery by modifying the adduct
group (AG) and LG with functional groups of differing electron-donating
and -withdrawing properties. We discovered the sulfur electrophile
is highly sensitive to the position of modification (AG versus LG),
which enabled both coarse and fine adjustments in solution and proteome
activity. We applied these reactivity principles to identify a large
fraction of tyrosine sites (∼30%) on proteins (∼44%)
that can be liganded across >1500 probe-modified sites quantified
by chemical proteomics. Our proteomic studies identified noncatalytic
tyrosine and phosphotyrosine sites that can be liganded by SuTEx fragments
with site specificity in lysates and live cells to disrupt protein
function. Collectively, we describe SuTEx as a versatile covalent
chemistry with broad applications for chemical proteomics and protein
ligand discovery.