Protein Trans-splicing Activities of Multiple Split Inteins Derived from Ssp GyrB Intein

Inteins are internal proteins inside precursor proteins and can be viewed as the protein equivalent of introns. Inteins catalyze a protein splicing reaction that excises the intein sequence from the precursor protein and joins the flanking sequences (N- and C-exteins) with a peptide bond. Split inteins, in which the intein sequence is broken into two pieces (IN and IC), can catalyze a trans-splicing reaction that joins the flanking exteins from two separate proteins. Protein trans-splicing has become a powerful tool of protein engineering, which have included fusion of separate polypeptides, segmental production and labeling of proteins, and site-specific addition of chemical modifications or labels to proteins. The Ssp GyrB intein has been particularly interesting, because it could be converted into an atypical split intein (S11 form) that could add synthetic peptides to the C-terminus of target proteins. In this study, we found that this intein could also be converted into other forms of split inteins, and a hexahistidine (H6) tag could be added for easy purification of the intein-containing proteins. An S1 form of the split intein can be particularly useful for adding synthetic peptides to the N-terminus of target proteins, while an overlapping form of the split intein could be advantageous in splicing together recombinant proteins.