A conserved threonine spring‐loads precursor for intein splicing

Protein splicing is an autocatalytic process where an “intein” self‐cleaves from a precursor and ligates the flanking N‐ and C‐“extein” polypeptides. Inteins occur in all domains of life and have myriad uses in biotechnology. Although the reaction steps of protein splicing are known, mechanistic det...

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Published inProtein science Vol. 22; no. 5; pp. 557 - 563
Main Authors Dearden, Albert K., Callahan, Brian, Roey, Patrick Van, Li, Zhong, Kumar, Utsav, Belfort, Marlene, Nayak, Saroj K.
Format Journal Article
LanguageEnglish
Published Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.05.2013
Wiley Subscription Services, Inc
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Summary:Protein splicing is an autocatalytic process where an “intein” self‐cleaves from a precursor and ligates the flanking N‐ and C‐“extein” polypeptides. Inteins occur in all domains of life and have myriad uses in biotechnology. Although the reaction steps of protein splicing are known, mechanistic details remain incomplete, particularly the initial peptide rearrangement at the N‐terminal extein/intein junction. Recently, we proposed that this transformation, an N‐S acyl shift, is accelerated by a localized conformational strain, between the intein's catalytic cysteine (Cys1) and the neighboring glycine (Gly‐1) in the N‐extein. That proposal was based on the crystal structure of a catalytically competent trapped precursor. Here, we define the structural origins and mechanistic relevance of the conformational strain using a combination of quantum mechanical simulations, mutational analysis, and X‐ray crystallography. Our results implicate a conserved, but largely unstudied, threonine residue of the Ssp DnaE intein (Thr69) as the mediator of conformational strain through hydrogen bonding. Further, the strain imposed by this residue is shown to position the splice junction in a manner that enhances the rate of the N‐S acyl shift substantially. Taken together, our results not only provide fundamental understanding of the control of the first step of protein splicing but also have important implications in various biotechnological applications that require precursor manipulation. PDB Code(s): 4GIG
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Grant sponsors: The Interconnect Focus Center funded by the MARCO program of SRC and the State of New York; Grant sponsor: NSF CBET; Grant number: 0931717; Grant sponsor: NIH; Grant number: GM44844.
Brian Callahan's current address is State University of New York at Binghamton Department of Chemistry, 4400 Vestal Parkway East Binghamton, NY 13902.
ISSN:0961-8368
1469-896X
DOI:10.1002/pro.2236