High-resolution structure of the presynaptic RAD51 filament on single-stranded DNA by electron cryo-microscopy.

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• Homologous DNA recombination (HR) is essential for error-free DNA repair, utilizing the RAD51 recombinase.
• RAD51 forms a presynaptic filament on single-stranded DNA to facilitate homologous pairing with double-stranded DNA.

Purpose of the Study:

• To determine the high-resolution structure of the presynaptic human RAD51 filament.
• To elucidate the structural mechanisms underlying RAD51 filament formation and its regulation by BRCA2.
• To understand the structural basis of RAD51 mutations associated with Fanconi anaemia-like diseases.

Main Methods:

• Electron cryo-microscopy was used to obtain the structure of the human RAD51 filament at 3.5-5.0Å resolution.
• Structural modeling was employed to predict binding sites for BRCA2 BRC repeats and analyze mutation effects.

Main Results:

• The structure reveals RAD51 encasing single-stranded DNA in a helical filament with specific pitch, protomer spacing, and rotational parameters.
• Inter-protomer distance is linked to the rotation of an α-helical region, suggesting a mechanism for modulating filament pitch.
• Predicted binding sites for BRCA2 BRC repeat modules on the filament were identified, explaining BRCA2's dual role in HR regulation.

Conclusions:

• The study provides a detailed structural model of the human RAD51 presynaptic filament, advancing our understanding of DNA repair.
• Insights into RAD51-DNA interactions and regulation by BRCA2 offer a mechanistic basis for HR processes and disease.
• The findings clarify the impact of RAD51 mutations in Fanconi anaemia-like diseases and the complex role of BRCA2 in HR.