The Recent Progresses in Chemical Synthesis of Proteins with Site-Specific Lysine Post-translational Modifications.

In the past two decades, a plethora of lysine (Lys) posttranslational modifications (PTMs) has been discovered on proteins, major groups are acylation, alkylation, and ubiquitination. Although considered biologically important, functional annotation of proteins with Lys PTMs has largely fallen behind the discovery. One grand challenge of characterizing proteins with PTMs is the procurement of homogenously modified proteins. To resolve this obstacle, sophisticated methods have been developed. These include total synthesis, semisynthesis that is based on native chemical ligation, expressed protein ligation, and enzyme-catalyzed peptide ligation, and the amber-suppression based noncanonical amino acid mutagenesis technique that may need to couple with follow-up bioorthogonal chemistry. This review summarizes currently identified significant PTMs and chemical biology methods for their installation in proteins. We hope that the current review will provide helpful insights and critical perspectives to this important research frontier.