Peptide expressed protein ligation

Figure 6 Schematic representation of protein ligation methods applied for the introduction of a lipidated peptide on proteins and an overview of the synthesized libraries of lipidated proteins as exemplified via Ras GTPases. (A) expressed protein ligation (EPL). (B) Maleimidocaproyl (MIC).

The technique of native chemical ligation (NCL) or expressed protein ligation (EPL) (42) tremendously expanded the scope of peptide/protein synthesis. This approach also has been adopted for the construction of neoglycoproteins. For complete synthetic... 

To extend the scope of NCL, efforts have been made to introduce modifications so as not to depend on a Cys site. Cys residues can be selectively desulfurized to Ala [124], even in the presence of Cys(Acm) and Met [125]. Homocysteine and selenocysteine also serve as ligation sites, and can then be converted into Met [126] and into Ala or didehydroalanine, respectively [127]. Recently, ligation at Phe sites has also been accomplished [128]. The use of auxiliaries that are removed after ligation has been extensively studied [129-134]. NCL has also been applied to SPPS [135, 136], and to the synthesis of cyclic peptides [137-139], In another extension of the technique, proteins have been prepared by tandem ligation [135, 140], and expressed protein ligation [141]. Recently, NCL has been applied to the synthesis of glycoproteins [104, 142-144]. 

Figure 8.8 Expressed protein ligation. The final step of protein splicing by the intein is inactivated by the mutation of the C-tenninal Asn to Ala. Proteins expressed as in-frame N-tenninal fusions to such mutant inteins can be cleaved by thiols to give corresponding protein (N-peptide) thioester derivatives. The tagged inteins are removed. The N-peptide thioesters can then react with an aCys-containing peptide (C-peptide)...

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