Human RAD52 is a coveted anticancer drug target. Its pharmacological inhibition is lethal to cancer cells displaying BRCAness phenotype and those deficient is ATM kinase fuction, while the RAD52 loss of function is well tolerated in normal cells. The challenges in targeting RAD52 include disrupring complex and extensive protein-DNA interactions, paucity of structural information and unsertainly as to exact cellular function of human RAD52 important to cancer cell survival.

RAD52 is involved in several cellular events that support genome stability including mutagenic single-strand annealing, mitotic DNA synthesis and maintenance of stalled DNA replication forks. As a gatekeeper of DNA replication forks RAD52 binds to and stabilizes stalled forks during replication stress protecting them from reversal by motor enzymes and subsequent degradation. Our structural, biochemical and single-molecule analyses revealed that the replication fork DNA promotes a unique nucleoprotein structure containing a spool-like, head-to-head arrangement of the two undecameric RAD52 rings with an extended positively charged surface that accommodates all three arms of the replication fork. In contrast, the strand annealing activity proceeds through side-by-side RAD52-ssDNA complexes and is enhanced by a phosphorylation event that disrupts the two-ring arrangement.

I will discuss our structural insights into RAD52-containing nucleoprotein complexes and our ongoing drug discovery campaign targeting human RAD52.