A University of Iowa-led research team has uncovered a previously unknown structure of the DNA repair protein RAD52, offering new insights that could aid the development of future anti-cancer drugs. The study, published in Nature on April 2, 2024, reveals how RAD52 binds and protects replicating DNA, helping cancer cells survive despite defects in their DNA repair mechanisms.
“RAD52 is a coveted drug target for treating cancers with DNA repair deficiencies, such as those linked to BRCA1 and BRCA2 mutations,” said Maria Spies, PhD, professor of biochemistry and molecular biology at the University of Iowa Carver College of Medicine and senior author of the study. “This protein is dispensable in healthy cells but becomes essential for survival in cancer cells that lack proper DNA repair pathways.”
Cancers with defective DNA repair often depend on backup systems like RAD52 to keep proliferating. Blocking RAD52 can therefore selectively destroy cancer cells while sparing healthy ones. Previous studies have shown that RAD52 inhibitors can kill cancer cells and reduce toxicity from radiation and chemotherapy, similar to PARP inhibitors such as olaparib. However, resistance to PARP inhibitors often develops, highlighting the need for new treatment strategies targeting RAD52.
The Iowa team, working with collaborators in Italy, has now revealed the molecular structure of RAD52 using cryogenic electron microscopy (CryoEM). Their analysis showed that RAD52 forms an unexpected spool-like double ring — two connected rings, each composed of 11 protein units — that binds to and stabilises DNA replication forks. This structure shields the DNA from harmful enzymatic activity, preserving its integrity during replication.
To capture the detailed 3D image, researchers engineered a DNA sample mimicking a stalled replication fork. This allowed them to visualise RAD52 interacting with all three DNA arms, confirming that both single- and double-stranded DNA components help stabilise the protein complex. Additional single-molecule imaging revealed that RAD52’s protection occurs through highly dynamic protein-DNA interactions.
“This is the first time we’ve seen RAD52 forming two rings together on DNA,” Spies explained. “The new structure provides clues about which regions of the protein can be targeted for drug development.”
The findings were supported by computational modelling from M. Ashley Spies of the UI College of Pharmacy and cellular studies led by Pietro Pichierri at the Istituto Superiore di Sanità in Rome. Together, the teams demonstrated that the two-ring structure is critical to RAD52’s DNA protection function and cancer cell survival.
“This study sets the foundation for developing new, more precise RAD52 inhibitors,” said Spies. “By understanding how this protein works, we move closer to creating next-generation therapies for hard-to-treat cancers.”