Cellular functions are defined by dynamic assembly, rearrangement, and disassembly of biomolecules to achieve control and specificity. As an example, effective DNA repair is brought about by the concerted action of several DNA processing proteins. Both changes in the structure of individual proteins and in the arrangement of multiple proteins together (referred to here as architecture) are inherent to biological function. These dynamic changes are exemplified in the breast cancer susceptibility protein 2 (BRCA2). BRCA2 is a DNA repair protein that undergoes changes in its own structure and affects changes in molecular architecture with partners during homologous recombination (HR) repair of DNA double strand breaks. These challenging features of BRCA2 protein, its size and predicted stretches of intrinsically disordered regions, have made it difficult to determine the structural consequences and mechanistic importance of interactions between full-length BRCA2 with RAD51 and other HR proteins. In this chapter, we describe scanning force microscopy (SFM)-based approaches to study DNA–protein complexes involved in HR, the architectural plasticity of full-length BRCA2, and the dynamic reorganization of these molecular components associated with essential steps of HR.@en

BRCA2 is a key breast cancer associated protein that is predicted to have interspersed regions of intrinsic disorder. Intrinsic disorder coupled with large size likely allows BRCA2 to sample a broad range of conformational space. We expect that the resulting dynamic arrangements of BRCA2 domains are a functionally important aspect of its role in homologous recombination DNA repair. To determine the architectural organization and the associated conformational landscape of BRCA2, we used scanning force microscopy based single molecule analyses to map the flexible regions of the protein and characterize which regions influence oligomerization. We show that the N- and the C-terminal regions are the main flexible regions. Both of these regions also influence BRCA2 oligomerization and interaction with RAD51. In the central Brc repeat region, Brc 1-4 and Brc 5-8 contribute synergistically to BRCA2 interaction with RAD51. We also analysed several single amino acid changes that are potentially clinically relevant and found one, the variant of F1524V, which disrupts key interactions and alters the conformational landscape of the protein. We describe the overall conformation spectrum of BRCA2, which suggests that dynamic structural transitions are key features of its biological function, maintaining genomic stability.@en