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. 1999 Dec;6(12):1096-9.
doi: 10.1038/70027.

A novel endonuclease mechanism directly visualized for I-PpoI

E A Galburt  1 , B Chevalier, W Tang, M S Jurica, K E Flick, R J Monnat Jr, B L Stoddard
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A novel endonuclease mechanism directly visualized for I-PpoI

E A Galburt et al. Nat Struct Biol. 1999 Dec.

Abstract

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.

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