The Tale of Two Inteins: Similar Inteins with Different C‐termini

Abstract

Protein splicing is a post‐translational process facilitated by an intervening polypeptide, or intein. The intein catalyzes its excision from the flanking polypeptides, or exteins, as well as ligation of the exteins. We studied inteins that interrupt the DNA Polymerase II from the cyanobacteria Synechococcus sp. PCC 7002 (Ssp) and Trichodesmium erythraeum (Tery). The two inteins differ mostly in the residues that promote the third step of splicing, side chain cyclization of the C‐terminal residue coupled to peptide bond cleavage. While the Ssp intein has a native C‐terminal Asn, the Tery intein has a native Gln. We hypothesized that the replacement of the native Asn with Gln might slow splicing, whereas replacement of the native Gln with Asn may accelerate splicing, as cyclization of Asn residues is usually considerably faster. Preliminary results suggest that our hypothesis is correct for isolated side chain cyclization, but that the overall splicing reaction is less affected by the identity of the C‐terminal residue. This suggests that conformational changes after step one, an amide to thioester rearrangement, might affect the rate of side‐chain cyclization.Support or Funding InformationThis material is based upon work supported by the National Science Foundation under grants MCB‐1244089 and MCB‐1517138, a Henry Dreyfus Teacher‐Scholar Award (KVM), and Mrs. Jeremiah W. O'Connor, Jr.