9ZZR

Cryo-EM Structure of a RAD51 filament bound by ssDNA and the XRCC3-RAD51C-RAD51D-XRCC2 paralog complex

Summary for 9ZZR

• Entry DOI: 10.2210/pdb9zzr/pdb
• EMDB information: 75014
• Descriptor: DNA repair protein RAD51 homolog 1, DNA (5'-D(P*TP*TP*TP*TP*TP*TP*TP*TP*TP*TP*TP*TP*TP*TP*TP*TP*TP*TP*TP*TP*TP*TP*T)-3'), DNA repair protein XRCC2, ... (9 entities in total)
• Functional Keywords: pentameric, rad51, xrcc3, rad51c, rad51d, xrcc2, dna binding protein-dna complex, dna binding protein/dna
• Biological source: Homo sapiens (human); More
• Total number of polymer chains: 12
• Total formula weight: 393364.13

Authors

Ruben, E.A.,Jia, L.,Olsen, S.K.,Wasmuth, E.V.,Rawal, Y.,Kwon, Y.,Sung, P. (deposition date: 2026-01-07, release date: 2026-04-01, Last modification date: 2026-06-17)

Primary citation

Rawal, Y.,Kwon, Y.,Jia, L.,Ruben, E.A.,Ji, J.H.,Guo, L.,Stratton, C.M.,Nayak, D.,Tovar, M.,Fang, Q.,Jamalruddin, M.A.,Zhou, S.,Kuppa, S.,Syed, S.,Jasper, A.M.,Katz, J.N.,Rogers, C.M.,Kaur, H.,Samentar, L.,Zhao, W.,Dray, E.,Zhang, F.,Stoilova-McPhie, S.,Taylor, A.B.,Burma, S.,Rao, M.K.,Libich, D.S.,Hromas, R.,Mazin, A.V.,Jasin, M.,Zhou, D.,Bernstein, K.A.,Greene, E.C.,Wasmuth, E.V.,Sung, P.,Olsen, S.K.
Structural insight into how RAD51 paralog exchange regulates RAD51 filament formation.
Nat.Struct.Mol.Biol., 33:768-781, 2026

PubMed Abstract: Homologous recombination (HR) repairs DNA double-strand breaks and stabilizes stressed replication forks, and HR deficiency promotes genome instability and cancer. HR requires assembly of RAD51 nucleoprotein filaments on single-stranded DNA (ssDNA), a process regulated by the human RAD51 paralogs RAD51C, XRCC3, RAD51D and XRCC2. Here, using cryo-electron microscopy, we find that the RAD51-XRCC3-RAD51C complex (RAD51-X3C) assembles into an octamer in which XRCC3 engages the RAD51 DNA-binding surface and RAD51 subunits adopt a misaligned configuration incompatible with filament formation. These features define an autoinhibited RAD51-X3C state that limits nonproductive RAD51 binding to double-stranded DNA or RNA-DNA hybrids while preserving RAD51 availability for ssDNA-dependent strand exchange. We further show that the RAD51D-XRCC2 paralog complex remodels RAD51-X3C into a pentameric RAD51-X3CDX2 assembly by engaging the exposed RAD51C surface and disrupting contacts that stabilize the octamer. This remodeling exposes the RAD51 DNA-binding interface, enhances RAD51-ssDNA filament assembly, and promotes strand exchange on RPA-coated ssDNA, and yields a filament-compatible paralog assembly that integrates into ssDNA-bound RAD51 filaments. Together, these findings establish paralog exchange as a mechanism that converts an autoinhibited RAD51-X3C octamer into an activated RAD51-X3CDX2 pentamer to regulate RAD51 filament formation during HR and replication fork preservation.

PubMed: 42020761
DOI: 10.1038/s41594-026-01796-6

Experimental method

ELECTRON MICROSCOPY (2.95 Å)