Abstract 1537 Mechanisms of BAZ2B Chromatin Remodeling at G Quadruplex DNA

Bromodomain Adjacent to Zinc finger 2B (BAZ2B) is a regulatory subunit member of the Imitation Switch (ISWI) chromatin remodeling family whose molecular activity has not been studied. Recent clinical characterizations suggest that BAZ2B haploinsufficiency contributes to neurodevelopmental disorders including autism spectrum disorder, developmental delay, and intellectual disability. We have identified BAZ2B as a novel regulator of G quadruplex (G4) DNA, a non-canonical nucleic acid secondary structure that can form in guanine-rich regions of the genome. G4 DNA has physiological roles in gene regulation, transcription, translation, and DNA replication. However, G4 DNA is also known to trigger genome instability and mutagenesis by disrupting cellular processes such as replication and transcription. The mechanisms by which G4 DNA formation and resolution is controlled are incompletely understood. BAZ2B is predicted to biochemically interact with either ISWI ATPase active subunits, SMARCA1 or SMARCA5, however, the members of the BAZ2B complex that regulate G4 DNA are not known. Here we show via Proximity Ligation Assays (PLA) that both SMARCA1 and SMARCA5 colocalize with G4 DNA in human cells. Our data shows that preferential binding of the BAZ2B-SMARCA5 complex occurs at G4s suggesting that this might be the complex important for G4 regulation. Measuring the spatial relationship between G4 DNA and BAZ2B will provide further insight into the identities of the chromatin remodeling complex that is relevant to G4 DNA regulation. To identify additional proteins in the BAZ2B interactome, we have established a customized proximity biotin labeling system, miniTurbo-BAZ2B, to covalently label proteins within 2-3 nanometers of BAZ2B in cells. Further exploration of the relationship between BAZ2B and G4 DNA regulation will contribute to an enhanced understanding of BAZ2B's function as a chromatin modifier and its effect on genome stability and neurodevelopment. This work was supported by the Northeastern University AJC Merit Research Scholarship, the Northeastern University Undergraduate Research and Fellowships Office Project-Based Exploration for the Advancement of Knowledge (PEAK) Trail-Blazer Award, and the Northeastern University College of Science Advancing Women in Science Award.