Expressed Protein Ligation and Inteins

Muir et al. (1998) realized that the intein reaction could be used to facilitate a native chemical ligation with a synthetic N-terminal cysteine-containing peptide or cysteine-containing molecule. With the discovery of a mutant intein that could form an intermediate thioester but not go on to complete the splice and ligation reaction (Xu and Perler, 1996 Chong et al., 

this expression technology now could be combined with the native chemical ligation reaction to facilitate a new Expressed Protein Ligation (EPL) method. 

Fusion vectors are available that combine a recombinant protein with a mutant mini intein segment (not containing an endonuclease domain) and followed by a chitin binding domain (CBD Zhang et al., 2001). These mutants typically also have an alanine substitution that replaces the cysteine or serine/threonine usually found on the C-extein splice junction. Alanine 

Protein-peptide ligation by amide bond formation 

EPL extends the applicability of native chemical ligation to recombinantly produced proteins using the mutant mini intein vector system. Proteins being expressed using this method will 

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