ABSTRACT
As internal protein elements , inteins are self-excised from their host protein and catalyze ligation of exteins with a peptide bond .They are widely found in all the three domains of the biological kingdom , and in viral proteins .Intein-mediated protein splicing is a posttranslational autocatalytic process that does not require auxiliary enzymes or cofactors . Protein splicing involves four intramolecular reactions and a small number of key catalytic residues in the intein and exteins . The development of expressed protein ligation ( EPL ) and protein trans-splicing ( PTS ) is assisted by inteins and protein splicing.This review introduces the biosynthesis of backbone-cyclized peptides libraries , and describes the applications of cyclic polypeptides and their prospective applications in the future .