标题：Semisynthesis of a segmental isotopically labeled protein splicing precursor: NMR evidence for an unusual peptide bond at the N-extein–intein junction
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2004
卷号：101
期号：17
页码：6397-6402
DOI：10.1073/pnas.0306616101
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：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 1JNC' coupling constant for the (-1) scissile peptide bond at the N-extein-intein junction was found to be {approx}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.
