title: An alternative protein splicing mechanism for inteins lacking an N-terminal nucleophile.
abstract: Variations in the intein-mediated protein splicing mechanism are becoming more apparent as polymorphisms in conserved catalytic residues are identified. The conserved Ser or Cys at the intein N-terminus and the conserved intein penultimate His are absent in the KlbA family of inteins. These inteins were predicted to be inactive, since an N-terminal Ala cannot perform the initial reaction of the standard protein splicing pathway to yield the requisite N-terminal splice junction (thio)ester. Despite the presence of an N-terminal Ala and a penultimate Ser, the KlbA inteins splice efficiently using an alternative protein splicing mechanism. In this non-canonical pathway, the C-extein nucleophile attacks a peptide bond at the N-terminal splice junction rather than a (thio)ester bond, alleviating the need to form the initial (thio)ester at the N-terminal splice junction. The remainder of the two pathways is the same: branch resolution by Asn cyclization is followed by an acyl rearrangement to form a native peptide bond between the ligated exteins.
authors.affiliation: New England BioLabs, 32 Tozer Road, Beverly, MA 01915, USA
authors.forename: M W
authors.initials: MW
authors.lastname: Southworth
authors.forename: J
authors.initials: J
authors.lastname: Benner
authors.forename: F B
authors.initials: FB
authors.lastname: Perler
mesh_terms: D000409:Alanine / Q000737:chemistry; D017398:Alternative Splicing; D001426:Bacterial Proteins; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism*; D002384:Catalysis; D002460:Cell Line; D003001:Cloning, Molecular; D003545:Cysteine / Q000737:chemistry*; D017017:Methanococcus / Q000235:genetics / Q000378:metabolism; D008957:Models, Genetic; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011110:Polymorphism, Genetic; D011499:Protein Processing, Post-Translational; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D012694:Serine / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D011993:Recombinant Fusion Proteins; C088797:klbA protein, Streptomyces lividans; D012694:Serine; D003545:Cysteine; D000409:Alanine