Main author: Sveinn Bjarnason
Institution or Company: University of Iceland, Science Institute
Co-Authors, Institution or Company:
Pétur Orri Heiðarsson, University of Iceland, Science Institute. Matthías Már Valdimarsson, University of Iceland, Science Institute.
Introduction: Sox2 is a pioneer transcription factor that has the unique ability to initiate cell fate changes by targeting and remodelling condensed, nucleosome-rich chromatin. Like most transcription factors Sox2 consists of a small, structured DNA binding domain (DBD) and long intrinsically disordered regions (IDRs) including the transactivation domain. Little is known about the molecular mechanism of nucleosome binding and opening, and whether the disordered regions are involved.
Methods: Single-molecule spectroscopy in combination with FRET (smFRET) is a powerful technique to study structured and disordered proteins and enables quantitative analysis of distances and dynamics over a wide time scale. We applied smFRET to study Sox2 interactions with DNA and reconstituted nucleosomes, by labelling either proteins or DNA with fluorophores and monitoring changes in FRET upon their interactions.
Results: We observed that full-size Sox2 causes increased bending of free DNA compared to only the DBD, indicating a specific role for the IDR in DNA binding. We found that Sox2 can bind to both free and histone H1-bound nucleosomes, leading to an open state of the nucleosome, with binding affinities that agree with previous studies.
Conclusions: Single-molecule spectroscopy can be used to successfully monitor the interactions of pTFs, DNA and nucleosomes. Using these methods, we observed that Sox2 targets and opens nucleosomes, displaces histone H1 and our preliminary results suggest that the IDRs are involved in DNA binding. Understanding the mechanism of this master transcription factor will impact designs of strategies to control cell identity.
