A novel endonuclease mechanism directly visualized for I-PpoI

E. A. Galburt, B. Chevalier, W. Tang, M. S. Jurica, K. E. Flick, Jr Monnat, B. L. Stoddard

Research output: Contribution to journalArticlepeer-review

96 Scopus citations


A novel mechanism of DNA endonucleolytic cleavage has been visualized for the homing endonuclease I-PpoI by trapping the uncleaved enzyme-substrate complex and comparing it to the previously visualized product complex. This enzyme employs a unique single metal mechanism. A magnesium ion is coordinated by an asparagine residue and two DNA oxygen atoms and stabilizes the phosphoanion transition state and the 3'oxygen leaving group. A hydrolytic water molecule is activated by a histidine residue for an in-line attack on the scissile phosphate. A strained enzyme-substrate-metal complex is formed before cleavage, then relaxed during the reaction.

Original languageEnglish
Pages (from-to)1096-1099
Number of pages4
JournalNature Structural Biology
Issue number12
StatePublished - 1999


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