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Proc Natl Acad Sci U S A. 2004 Apr 27;101(17):6397-402. Epub 2004 Apr 15.

Semisynthesis of a segmental isotopically labeled protein splicing precursor: NMR evidence for an unusual peptide bond at the N-extein-intein junction.

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Laboratory of Synthetic Protein Chemistry, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.


Protein splicing is a posttranslational autocatalytic process in which an intervening sequence, termed an intein, is removed from a host protein, the extein. Although we have a reasonable picture of the basic chemical steps in protein splicing, our knowledge of how these are catalyzed and regulated is less well developed. In the current study, a combination of NMR spectroscopy and segmental isotopic labeling has been used to study the structure of an active protein splicing precursor, corresponding to an N-extein fusion of the Mxe GyrA intein. The (1)J(NC') coupling constant for the (-1) scissile peptide bond at the N-extein-intein junction was found to be approximately 12 Hz, which indicates that this amide is highly polarized, perhaps because of nonplanarity. Additional mutagenesis and NMR studies indicate that conserved box B histidine residue is essential for catalysis of the first step of splicing and for maintaining the (-1) scissile bond in its unusual conformation. Overall, these studies support the "ground-state destabilization" model as part of the mechanism of catalysis.

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