Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.09.28.313049v1?rss=1 Authors: Paul, D., Mu, H., Tavakoli, A., Dai, Q., Chen, X., Chakraborty, S., He, C., Ansari, A., Broyde, S., Min, J. H. Abstract: XPC/Rad4 initiates eukaryotic nucleotide excision repair on structurally diverse helix-destabilizing/distorting DNA lesions by selectively 'opening' these sites while rapidly diffusing along undamaged DNA. Previous structural studies showed that Rad4, when tethered to DNA, could also open undamaged DNA, suggesting a 'kinetic gating' mechanism whereby lesion discrimination relied on efficient opening versus diffusion. However, solution studies in support of such a mechanism were lacking and how 'opening' is brought about remained unclear. Here, we present crystal structures and fluorescence-based conformational analyses on tethered complexes, showing that Rad4 can indeed 'open' undamaged DNA in solution and that such 'opening' can largely occur without one or the other of the {beta}-hairpin motifs in the BHD2 or BHD3 domains. Notably, the Rad4-bound 'open' DNA adopts multiple conformations in solution notwithstanding the DNA's original structure or the {beta}-hairpins. Molecular dynamics simulations reveal compensatory roles of the {beta}-hairpins, which may render robustness in dealing with and opening diverse lesions. Our study showcases how fluorescence-based studies can be used to obtain information complementary to ensemble structural studies. The tethering-facilitated DNA 'opening' of undamaged sites and the dynamic nature of 'open' DNA may shed light on how the protein functions within and beyond NER in cells. Copy rights belong to original authors. Visit the link for more info