PMID: 15077103 , Related PDB ids: 1UT5, 1UT8

Authors:

Feng M, Patel D, Dervan JJ, Ceska T, Suck D, Haq I, Sayers JR

Title:

Roles of divalent metal ions in flap endonuclease-substrate interactions.

Journal:

Nat Struct Mol Biol. 2004 May;11(5):450-6. Epub 2004 Apr 11.

Abstract:

Flap endonucleases (FENs) have essential roles in DNA processing. They catalyze exonucleolytic and structure-specific endonucleolytic DNA cleavage reactions. Divalent metal ions are essential cofactors in both reactions. The crystal structure of FEN shows that the protein has two conserved metal-binding sites. Mutations in site I caused complete loss of catalytic activity. Mutation of crucial aspartates in site II abolished exonuclease action, but caused enzymes to retain structure-specific (flap endonuclease) activity. Isothermal titration calorimetry revealed that site I has a 30-fold higher affinity for cofactor than site II. Structure-specific endonuclease activity requires binding of a single metal ion in the high-affinity site, whereas exonuclease activity requires that both the high- and low-affinity sites be occupied by divalent cofactor. The data suggest that a novel two-metal mechanism operates in the FEN-catalyzed exonucleolytic reaction. These results raise the possibility that local concentrations of free cofactor could influence the endo- or exonucleolytic pathway in vivo.