title: Structural insights into the protein splicing mechanism of PI-SceI.
abstract: PI-SceI is a member of a class of proteins (inteins) that excise themselves from a precursor protein and in the process ligate the flanking protein sequences (exteins). We report here the 2.1-A resolution crystal structure of a PI-SceI miniprecursor (VMA29) containing 10 N-terminal extein residues and 4 C-terminal extein residues. Mutations at the N- and C-terminal splicing junctions, blocking in vivo protein splicing, allowed the miniprecursor to be purified and crystallized. The structure reveals both the N- and C-terminal scissile peptide bonds to be in distorted trans conformations (tau approximately 100 degrees ). Modeling of the wild-type PI-SceI based on the VMA29 structure indicates a large conformational change (movement of >9 A) must occur to allow transesterification to be completed. A zinc atom was discovered at the C-terminal splicing junction. Residues Cys(455), His(453), and Glu(80) along with a water molecule (Wat(53)) chelate the zinc atom. The crystal structure of VMA29 has captured the intein in its pre-spliced state.
authors.affiliation: Howard Hughes Medical Institute and Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: B W
authors.initials: BW
authors.lastname: Poland
authors.forename: M Q
authors.initials: MQ
authors.lastname: Xu
authors.forename: F A
authors.initials: FA
authors.lastname: Quiocho
mesh_terms: D000595:Amino Acid Sequence; D003461:Crystallography; D015252:Deoxyribonucleases, Type II Site-Specific / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D019154:Protein Splicing; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid
chemical_list: D029701:Saccharomyces cerevisiae Proteins; C037725:SCEI protein, S cerevisiae; D015252:Deoxyribonucleases, Type II Site-Specific