image: Cryo-EM reconstructions of the human ATR–ATRIP complex show how clinical small-molecule inhibitors like VE-822 and RP-3500 bind to and inhibit ATR activity.
Credit: © University of Science & Technology of China
A research team led by Prof. Gang Cai and Prof. Xuejuan Wang at the University of Science and Technology of China has made a groundbreaking discovery by determining the first near-atomic-resolution structure of the full-length human ATR–ATRIP complex in complex with two ATR inhibitors currently undergoing clinical trials. This work sheds light on the mechanisms through which ATR maintains genomic stability and how its inhibition can be leveraged for precision cancer therapy.
ATR (ataxia telangiectasia and Rad3-related protein) is a key kinase that plays a central role in responding to DNA replication stress and single-stranded DNA damage. Disruption of ATR function is closely linked to genomic instability and tumorigenesis. However, due to the technical difficulty in preparing stable ATR–ATRIP samples, only a low-resolution model had previously been available, leaving critical aspects of ATRIP stoichiometry and ATR’s regulation poorly understood.
To address this gap, the team employed cryo-electron microscopy (cryo-EM) to reconstruct the complete structure of the human ATR–ATRIP complex at near-atomic resolution. The results clarified key structural features, such as the organization of ATR’s large N-terminal region and the complete topology of ATRIP. The study identified multiple interaction interfaces, including novel inter-subunit disulfide bonds and a zinc finger structure within ATRIP, providing the first clear picture of how this complex is assembled and stabilized.
Importantly, the researchers analyzed how two clinical ATR inhibitors—VE-822 and RP-3500—interact with the ATR–ATRIP complex. VE-822 was found to induce significant conformational changes in the kinase domain, with up to four VE-822 molecules binding per dimer. In contrast, RP-3500 exhibited a unique binding mode that involves coordination with two water molecules. These findings reveal previously unknown structural selectivity and provide a blueprint for designing next-generation ATR inhibitors.
This work not only enhances our understanding of ATR biology but also has profound implications for improving the efficacy and specificity of ATR-targeted cancer therapies.