Allosteric regulation of DNA cleavage and sequence-specificity through run-on oligomerization.

Dmitry Lyumkis, Heather Talley, Andrew Stewart, Santosh Shah, Chad K Park, Florence Tama, Clinton S Potter, Bridget Carragher, Nancy C Horton

Index: Structure 21(10) , 1848-58, (2013)

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Abstract

SgrAI is a sequence specific DNA endonuclease that functions through an unusual enzymatic mechanism that is allosterically activated 200- to 500-fold by effector DNA, with a concomitant expansion of its DNA sequence specificity. Using single-particle transmission electron microscopy to reconstruct distinct populations of SgrAI oligomers, we show that in the presence of allosteric, activating DNA, the enzyme forms regular, repeating helical structures characterized by the addition of DNA-binding dimeric SgrAI subunits in a run-on manner. We also present the structure of oligomeric SgrAI at 8.6 Å resolution, demonstrating the conformational state of SgrAI in its activated form. Activated and oligomeric SgrAI displays key protein-protein interactions near the helix axis between its N termini, as well as allosteric protein-DNA interactions that are required for enzymatic activation. The hybrid approach reveals an unusual mechanism of enzyme activation that explains SgrAI's oligomerization and allosteric behavior.Copyright © 2013 Elsevier Ltd. All rights reserved.