A journey toward Bioorthogonal Profiling of Protein Methylation inside living cells.

Human protein methyltransferases (PMTs) play essential roles through methylating histone and nonhistone targets. It is very challenging to profile global methylation (or methylome) in the context of relevant cellular settings. Unlike other posttranslational modifications such as lysine acetylation or Ser/Thr/Tyr/His phosphorylation, methylation of lysine or arginine does not significantly alter its physical properties (e.g. charge and size) and therefore may not be probed readily by conventional biological tools such antibodies. It is also not trivial to assign unambiguously dynamic methylation events to specific PMTs given their potential redundancy. This review focuses on the decade-long progress in developing complementary chemical tools to elucidate targets of designated PMTs. One of such efforts was to develop the Bioorthogonal Profiling of Protein Methylation (BPPM) technology in vitro and inside living cells.