Intein native cleavage reaction

Figure 17.26 The native process leading to intein excision and ligation of extein fragments involves a sequence of reactions involving transthioesterification, cleavage of the intein fragment, and aS->N shift, which ligates the two extein peptides together via an amide bond.

Figure 17.28 EPL reactions can be used to couple a fusion protein to a surface containing a thioester derivative. After cells are grown and the fusion protein expressed, a pH and temperature shift causes intein cleavage with release of the expressed protein with an N-terminal cysteine residue. Reaction with the thioester surface results in a native chemical ligation reaction that forms an amide bond linkage with the expressed protein.

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