Crystal structure of an octameric RuvA-Holliday junction complex

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• Holliday junctions are critical intermediates in homologous recombination and DNA repair pathways.
• The bacterial RuvABC system resolves these junctions, with RuvAB facilitating branch migration and RuvC performing strand nicking.

Purpose of the Study:

• To determine the crystal structure of the complex between the RuvA protein and a synthetic four-way DNA junction.
• To elucidate the structural basis of RuvA's role in Holliday junction resolution.

Main Methods:

• X-ray crystallography was used to determine the structure of the RuvA-DNA complex.
• Analysis of the crystal structure focused on protein-DNA interactions and quaternary structure.

Main Results:

• The DNA is sandwiched between two RuvA tetramers, forming a closed octameric shell, contrary to previous suggestions of binding to an open surface.
• A conserved tetramer-tetramer interface stabilizes this octameric structure.
• Interactions between the DNA backbone and helix-hairpin-helix motifs within RuvA suggest a strand separation mechanism.

Conclusions:

• The RuvA protein forms a closed octameric complex to bind Holliday junctions.
• This structure provides insights into the mechanism of strand separation during DNA repair mediated by RuvA.
• The findings refine our understanding of the RuvABC system's function in bacteria.