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. 2025 Jun 5;85(11):2080-2096.e6.
doi: 10.1016/j.molcel.2025.05.010. Epub 2025 May 28.

BRCA2 C-terminal clamp restructures RAD51 dimers to bind B-DNA for replication fork stability

Michael A Longo  1 , Syed Moiz Ahmed  2 , Yue Chen  3 , Chi-Lin Tsai  1 , Sarita Namjoshi  1 , Runze Shen  1 , Zamal Ahmed  1 , Xiaoyan Wang  1 , Rajika L Perera  4 , Andy Arvai  5 , Miyoung Lee  6 , Li Ren Kong  7 , Wilfried Engl  8 , Woei Shyuan Ng  8 , Ziqing Winston Zhao  9 , Ashok R Venkitaraman  10 , John A Tainer  11 , Katharina Schlacher  12
Affiliations

BRCA2 C-terminal clamp restructures RAD51 dimers to bind B-DNA for replication fork stability

Michael A Longo et al. Mol Cell. .

Abstract

Tumor suppressor protein breast cancer susceptibility protein 2 (BRCA2) acts with RAD51 in replication fork protection (FP) and homology-directed DNA-break repair (HDR). Critical for cancer etiology and therapy resistance, the BRCA2 C terminus was thought to stabilize recombinogenic RAD51 after the assembly of ATP-extended RAD51 filaments on single-stranded DNA (ssDNA). Here, the detailed crystal structure of the human BRCA2 C-terminal interaction domain (TR2 interface [TR2i]) complexed with ATP-bound RAD51 prior to DNA binding instead reveals TR2i unexpectedly induces a unique ATP-RAD51 dimer conformation that accommodates nucleation onto double-stranded B-DNA unsuited for HDR initiation. Structural, biochemical, and molecular results with interface-guided mutations uncover TR2i's FP mechanism. Proline-driven secondary structure stabilizes residue triads and spans the RAD51 dimer, engaging pivotal interactions of RAD51 M210 and BRCA2 S3291/P3292, the cyclin-dependent kinase (CDK) phosphorylation site that toggles between FP during S phase and HDR in G2. TR2i evidently acts as an allosteric clamp, switching RAD51 from ssDNA to double-stranded and B-DNA binding, enforcing FP over HDR, challenging the current BRCA2-RAD51 dogma.

Keywords: BRCA2; Rad51; SIRF; cancer; crystal structure; genome stability; homology-directed repair; replication fork protection.

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Conflict of interest statement

Declaration of interests The authors declare no competing interests.

Update of

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