4C3G: Cryo-em Structure Of Activated And Oligomeric Restriction Endonuclease Sgrai

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 A 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.
PDB ID: 4C3GDownload
MMDB ID: 113354
PDB Deposition Date: 2013/8/23
Updated in MMDB: 2013/10
Experimental Method:
electron microscopy
Resolution: 8.6  Å
Source Organism:
Similar Structures:
Biological Unit for 4C3G: hexameric; determined by author
Molecular Components in 4C3G
Label Count Molecule
Proteins (2 molecules)
Sgrair Restriction Enzyme
Molecule annotation
Nucleotides(2 molecules)
5'-d(*gp*ap*tp*gp*cp*gp*tp*gp*gp*gp*tp*cp*tp*tp *cp*ap*cp*ap)-3'
Molecule annotation
5'-d(*cp*cp*gp*gp*tp*gp*tp*gp*ap*ap*gp*ap*cp*cp *cp*ap*cp*gp*cp*ap*tp*cp)-3'
Molecule annotation
* Click molecule labels to explore molecular sequence information.

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