High precision FRET studies reveal reversible transitions in nucleosomes between microseconds and minutes

• DOI: 10.1038/s41467-018-06758-1
• Publication Date: 2018-10-31T10:08:28Z
• Authors: Alexander Gansen; Suren Felekyan; Ralf Kühnemuth; Kathrin Lehmann; Katalin Tóth; Claus A. M. Seidel; Jörg Langowski
• Keywords: Models, Molecular; 0301 basic medicine; Photons; Protein Conformation; Science; Q; DNA; Sodium Chloride; Chromatin Assembly and Disassembly; Article; Fluorescence; Nucleosomes; Histones; Kinetics; 03 medical and health sciences; Energy Transfer; Mutation; Fluorescence Resonance Energy Transfer; Thermodynamics; Protein Multimerization; Biologie; Dimerization

AbstractNucleosomes play a dual role in compacting the genome and regulating the access to DNA. To unravel the underlying mechanism, we study fluorescently labeled mononucleosomes by multi-parameter FRET measurements and characterize their structural and dynamic heterogeneity upon NaCl-induced destabilization. Species-selective fluorescence lifetime analysis and dynamic photon distribution analysis reveal intermediates during nucleosome opening and lead to a coherent structural and kinetic model. In dynamic octasomes and hexasomes the interface between the H2A-H2B dimers and the (H3-H4)2 tetramer opens asymmetrically by an angle of ≈20° on a 50 and 15 µs time scale, respectively. This is followed by a slower stepwise release of the dimers coupled with DNA unwrapping. A mutation (H2A-R81A) at the interface between H2A and H3 facilitates initial opening, confirming the central role of the dimer:tetramer interface for nucleosome stability. Partially opened states such as those described here might serve as convenient nucleation sites for DNA-recognizing proteins.