Oxidant-Induced Bioconjugation for Protein Labeling in Live Cells

Chemical proteomics is a powerful technology that can
be used in
the studies of the functions of uncharacterized proteins in the human
proteome. It relies on a suitable bioconjugation strategy for protein
labeling. This could be either a UV-responsive photo-crosslinker or
an electrophilic warhead embedded in chemical probes that can form
covalent bonds with target proteins. Here, we report a new protein-labeling
strategy in which a nitrile oxide, a highly reactive intermediate
that reacts with proteins, can be efficiently generated by the treatment
of oximes with a water-soluble and a minimally toxic oxidant, phenyliodine
bis (trifluoroacetate) (PIFA). The resulting intermediate can rapidly
bioconjugate with amino acid residues of target proteins, thus enabling
target identification of oxime-containing bioactive molecules. Excellent
chemoselectivity of cysteine residues by the nitrile oxide was observed,
and over 4000 reactive and/or accessible cysteines, including KRAS
G12C, have been successfully characterized by quantitative chemical
proteomics. Some of these residues could not be detected by conventional
cysteine reagents, thus demonstrating the complementary utility of
this method.