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TITLE Dynamic coordination of two-metal-ions orchestrates lambda-exonuclease catalysis
KIAS AUTHORS Hyeon, Changbong,Hwang, Wonseok
JOURNAL NATURE COMMUNICATIONS, 2018
ARCHIVE  
ABSTRACT Metal ions at the active site of an enzyme act as cofactors, and their dynamic fluctuations can potentially influence enzyme activity. Here, we use lambda-exonuclease as a model enzyme with two Mg2+ binding sites and probe activity at various concentrations of magnesium by single-molecule-FRET. We find that while Mg-A(2+) and Mg-B(2+) have similar binding constants, the dissociation rate of Mg-A(2+) is two order of magnitude lower than that of Mg-B(2+) due to a kinetic-barrier-difference. At physiological Mg2+ concentration, the Mg-B(2+) ion near the 5'-terminal side of the scissile phosphate dissociates each-round of degradation, facilitating a series of DNA cleavages via fast product-release concomitant with enzyme-translocation. At a low magnesium concentration, occasional dissociation and slow re-coordination of Mg-A(2+) result in pauses during processive degradation. Our study highlights the importance of metal-ion-coordination dynamics in correlation with the enzymatic reaction-steps, and offers insights into the origin of dynamic heterogeneity in enzymatic catalysis.
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