Title: Redefining Non-Homologous End Joining DNA-repair using Cryo-electron Microscopy
Speaker: Amanda Chaplin, Lecturer in Structural Biology at the University of Leicester, UK
Abstract:
Cellular DNA is exposed to multiple sources of damaging agents, including endogenous sources such as oxidation and exogenous sources such as radiation. DNA repair mechanisms are vital as DNA double-strand breaks (DSBs) can cause cell death and eventually cancer if left unrepaired. Non-homologous end joining (NHEJ) is one of the two mechanisms required for DSB repair. NHEJ is dependent on several canonical proteins, namely DNA-PKcs, Ku70/80, DNA Ligase IV, XRCC4 and XLF, in addition to several regulatory proteins. Traditionally, NHEJ was thought to consist of three simple linear steps. However, recent cryo-EM data has provided an unexpected glimpse of alternate complex protein arrangements, leading us to propose that the mechanism of NHEJ is more complicated that originally believed. We have identified two alternate long-range DNA-PK dimers, one mediated by Ku80 and the other by XLF. These dimers are essential for efficient DNA repair. We have also recently shown that the accessory protein, PAXX can stabilise specifically the Ku80 DNA-PK dimer and how this has overlapping roles with XLF. Furthermore, we have used cryo-EM to visualise small molecules such as IP6 binding and DNA-PKcs inhibitors, which will aid in future therapeutic development.