Latent
electrophiles are nowadays very attractive chemical entities
for drug discovery, as they are unreactive unless activated upon binding
with the specific target. In this work, the utility of 4-trifluoromethyl
phenols as precursors of latent electrophiles, quinone methides (QM),
for lysine-targeting is demonstrated. These Michael acceptors were
photogenerated for specific covalent modification of lysine residues
using human serum albumin (HSA) as a model target. The reactive QM-type
intermediates I or II, generated upon irradiation
of 4-trifluoromethyl-1-naphthol (1)@HSA or 4-(4-trifluorometylphenyl)phenol
(2)@HSA complexes, exhibited chemoselective reactivity
toward lysine residues leading to amide adducts, which was confirmed
by proteomic analysis. For ligand 1, the covalent modification
of residues Lys106 and Lys414 (located in subdomains IA and IIIA,
respectively) was observed, whereas for ligand 2, the
modification of Lys195 (in subdomain IIA) took place. Docking and
molecular dynamics simulation studies provided an insight into the
molecular basis of the selectivity of 1 and 2 for these HSA subdomains and the covalent modification mechanism.
These studies open the opportunity of performing protein silencing
by generating reactive ligands under very mild conditions (irradiation)
for specific covalent modification of hidden lysine residues.
Triflusal is a platelet antiaggregant employed for the treatment and prevention of thromboembolic diseases. After administration, it is biotransformed into its active metabolite, the 2-hydroxy-4-trifluoromethylbenzoic acid (HTB). We present here an investigation on HTB photobinding to human serum albumin (HSA), the most abundant protein in plasma, using an approach that combines fluorescence, MS/MS, and peptide fingerprint analysis as well as theoretical calculations (docking and molecular dynamics simulation studies). The proteomic analysis of HTB/HSA photolysates shows that HTB addition takes place at the ε-amino groups of the Lys137, Lys199, Lys205, Lys351, Lys432, Lys525, Lys541 and Lys545 residues and involves replacement of the trifluoromethyl moiety of HTB with a new amide function. Only Lys199 is located in an internal pocket of the protein, and the remaining modified residues are placed in the external part. Docking and molecular dynamic simulation studies reveal that HTB supramolecular binding to HSA occurs in the “V-cleft” region and that the process is assisted by the presence of Glu/Asp residues in the neighborhood of the external Lys, in agreement with the experimentally observed modifications. In principle, photobinding can occur with other trifluoroaromatic compounds and may be responsible for the appearance of undesired photoallergic side effects.
Singlet oxygen photosensitization (studied by time-resolved near-infrared emission spectroscopy) and in vitro phototoxicity (by means of the 3T3 neutral red uptake
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