Fig. 22.
Intein-based chemical conjugation. a Expressed protein ligation (EPL) is a semisynthetic version of NCL in which synthetic and recombinant polypeptides are chemically ligated together. Proteins (A) expressed as intein fusions can be cleaved from the intein with a variety of thiols to give the corresponding α-thioester derivative. Proteins (B) containing N-terminal Cys can be made recombinantly by masking the Cys with a protease tag that can be later removed. b Protein trans-splicing (PTS) post-translationally links two protein fragments. An intein domain is split into two fragments, IntN and IntC, which are fused to the flanking exteins, ExN and ExC. ExN–IntN and IntC–ExC associate and fold to form a functional intein. This functional intein can restore protein splicing activity to excise itself, and to conjugate ExN and ExC with a peptide bond
(Figures adapted with permission from: Ref. [106]. Copyright (2012) Springer)