Nonenzymatic acetylation of ubiquitin Lys side chains is modulated by their neighboring residues

Nonenzymatic acetylation of Lys side chains (Lys-SCs) by various in vivo reactive molecules has been suggested to play novel regulatory roles. Ubiquitin (UB) has seven Lys residues that are utilized for synthesis of specific poly-UB chains. To understand the nature of these Lys-SC modifications, the chemical acetylation rate and pKa and Hill coefficient of each UB-Lys-SC were measured. Mutagenesis studies combined with the determination of activation energy indicated that specific neighboring residues of the Lys-SCs have a potential catalytic activity during nonenzymatic acetylation. Based on the shared chemistry between nonenzymatic Lys acetylation and ubiquitylation, the characterized chemical properties of the UB-Lys-SCs could be a reference for deciphering both mechanisms. Our NMR approaches could be useful for studying general nonenzymatic Lys acylations of various proteins.