title: Interaction studies and alanine scanning analysis of a semi-synthetic split intein reveal thiazoline ring formation from an intermediate of the protein splicing reaction.
abstract: We recently reported an artificially split intein based on the Ssp DnaB mini-intein that consists of a synthetic N-terminal intein fragment (Int(N)) and a recombinant C-terminal part (Int(C)), which are 11 and 143 amino acids in length, respectively. This intein holds great promise for the preparation of semi-synthetic proteins by protein trans-splicing. In this work we synthesized a set of Int(N) peptide variants to investigate their structure-function relationship with regard to fragment association and promotion of protein trans-splicing. A further truncation of the Int(N) sequence below 11 amino acids resulted in loss of activity, whereas C-terminal extensions were tolerated. Alanine scanning analysis identified three essential hydrophobic residues, whereas substitutions at other positions were tolerated. We developed assays to monitor association of Int(N) with an Int(C) mutant blocked in protein splicing by native PAGE and fluorescence anisotropy. The kinetic parameters of intein complex formation were K(d) = 1.1 mum, k(on) = 16.8 m(-1) s(-1), and k(off) = 1.8 x 10(-5) s(-1) for the native Int(N11) sequence. Intriguingly, a G(-1)A substitution, previously known to significantly impair protein splicing, was revealed to result in thiazoline ring formation involving the catalytic Cys-1, likely by aberrant dehydration of a oxythiazolidine intermediate. This finding provides experimental evidence for the postulated intermediate during the initial N/S acyl shift and underlines the delicate spatial and temporal alignment required in the intein active site to prevent side reactions of the protein-splicing pathway.
authors.affiliation: Fakultät Chemie/Chemische Biologie, Technische Universität Dortmund, 44227 Dortmund, Germany.
authors.forename: Christina
authors.initials: C
authors.lastname: Ludwig
authors.affiliation: Fakultät Chemie/Chemische Biologie, Technische Universität Dortmund, 44227 Dortmund, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Schwarzer
authors.affiliation: Fakultät Chemie/Chemische Biologie, Technische Universität Dortmund, 44227 Dortmund, Germany. Electronic address: henning.mootz@uni-dortmund.de.
authors.forename: Henning D
authors.initials: HD
authors.lastname: Mootz
mesh_terms: D000409:Alanine / Q000737:chemistry*; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D047668:Inteins; D007700:Kinetics; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods; D013844:Thiazoles / Q000737:chemistry*; D053778:Thiazolidines / Q000737:chemistry
chemical_list: D010455:Peptides; D011506:Proteins; D013844:Thiazoles; D053778:Thiazolidines; D000409:Alanine