Covalent Protein Labeling at Glutamic Acids

Abstract

Covalent labeling of amino acids in proteins by reactive small molecules, in particular at cysteine SH and lysine NH groups, is a powerful approach to identify and characterize proteins and their functions. However, for the less-reactive carboxylic acids present in Asp and Glu, hardly any methodology is available. Employing the lipoprotein binding chaperone PDE6δ as an example, we demonstrate that incorporation of isoxazolium salts that resemble the structure and reactivity of Woodward's reagent K into protein ligands provides a novel method for selective covalent targeting of binding site carboxylic acids in whole proteomes. Covalent adduct formation occurs via rapid formation of enol esters and the covalent bond is stable even in the presence of strong nucleophiles. This new method promises to open up hitherto unexplored opportunities for chemical biology research.

Recent Progress in Chemical Modification of Proteins

“…Waldomann and coworkers reported a unique covalent inhibitor using isoxazolium salts that resemble Woodward's reagent K. This inhibitor formed a stable covalent bond with Asp and Glu present in a binding site of POI. 206 Kelly and coworkers explored an "Inverse Drug Discovery" strategy by employing aryl fluorosulfonates as latent electrophiles, which are essentially unreactive toward the vast majority of proteome, but activated only under certain circumstances. 207,208 They demonstrated that compounds possessing aryl fluorosulfonates react with Lys or Tyr side chains in proximity to cationic residues of ligand binding sites.…”

Reaktive chemische Sonden: Jenseits des Kinase‐Cysteinoms

“…In den vergangenen Jahren wurde über einige neuartige chemische Sonden mit Gefechtsköpfen berichtet, die andere Reste als Cystein oder Lysin anvisieren, nämlich Tyrosin, Serin und sogar Glutamat …”

Covalent Small Molecules as Enabling Platforms for Drug Discovery

“…Histidine has been shown to react with epoxides, sulfonyl fluorides, α,β‐unsaturated systems, and phosphorus‐based reagents . The acidic side chains aspartic acid and glutamic acid have seen limited exposure in the literature, although warheads based on Woodward's reagent K have shown recent promise . Methionine does not possess the inherent nucleophilicity of cysteine, explaining its limited attention to date.…”