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. Author manuscript; available in PMC: 2022 Oct 1.
Published in final edited form as: Curr Opin Chem Biol. 2021 Jun 25;64:76–89. doi: 10.1016/j.cbpa.2021.05.007

Figure 2. Protein ligation techniques for the synthetic installation of PTMs.

Figure 2.

a) Native chemical ligation (NCL) is the selective reaction of a peptide containing a C-terminal thioester and another peptide with an N-terminal cysteine. The ligation begins with a reversible transthioesterification reaction followed by an C to N acyl-shift to generate a native amide bond. b) Expressed protein ligation (EPL) extends the power of NCL through the generation of recombinant protein thioesters. Specifically, protein fragments can be recombinantly expressed as N-terminal fusions to a mutant intein protein. This results in the formation of a protein-intein thioester bond that can be intercepted by exogenous thiols.