Posttranslational modifications (PTMs) of proteins play
central
roles in regulating the protein structure, interactome, and functions.
A notable modification site is the aromatic side chain of Tyr, which
undergoes modifications such as phosphorylation and nitration. Despite
the biological and physiological importance of Tyr-PTMs, our current
understanding of the mechanisms by which these modifications contribute
to human health and disease remains incomplete. This knowledge gap
arises from the absence of natural amino acids that can mimic these
PTMs and the lack of synthetic tools for the site-specific introduction
of aromatic PTMs into proteins. Herein, we describe a facile method
for the site-specific chemical installation of aromatic PTMs into
proteins through palladium-mediated S–C(sp
2
) bond
formation under ambient conditions. We demonstrate the incorporation
of novel PTMs such as Tyr-nitration and phosphorylation analogs to
synthetic and recombinantly expressed Cys-containing peptides and
proteins within minutes and in good yields. To demonstrate the versatility
of our approach, we employed it to prepare 10 site-specifically modified
proteins, including nitrated and phosphorylated analogs of Myc and
Max proteins. Furthermore, we prepared a focused library of site-specifically
nitrated and phosphorylated α–synuclein (α-Syn)
protein, which enabled, for the first time, deciphering the role of
these competing modifications in regulating α-Syn conformation
aggregation in vitro. Our strategy offers advantages over synthetic
or semisynthetic approaches, as it enables rapid and selective transfer
of rarely explored aromatic PTMs into recombinant proteins, thus facilitating
the generation of novel libraries of homogeneous posttranslationally
modified proteins for biomarker discovery, mechanistic studies, and
drug discovery.