Mechanism of atp dependent chromatin modelling and editing by ino80 remodellers
Nucleosomes, ~147 base pairs of DNA wrapped around an histone protein octamer, package and protect nuclear DNA but also carry important biological information. The position and composition of nucleosomes along chromosomal DNA is a key element of defining the state and identity of a cell. Chromatin remodellers are ATP dependent molecular machines that position, move or edit nucleosomes in a genome wide manner. Collectively, they shape the nucleosome landscape and play central roles in the maintenance and differentiation of cells, but also in pathological transformations. INO80, a megadalton large remodeller consisting of 15 or more subunits, is involved in replication, gene expression and DNA repair. It models chromatin by positioning barrier nucleosomes around nucleosome free regions, editing nucleosomes and generating nucleosome arrays. However, structural mechanisms for INO80 and other remodelling machines are poorly understood due to their complexity. To provide a comprehensive mechanistic framework, to understand how INO80 senses nucleosome free regions to position barrier nucleosomes and how it generates arrays or senses DNA breaks, I propose a challenging but ground-breaking endeavour using a combination of cryo-EM and functional approaches. We address structures of fungal and human INO80 complexes at promoter regions, on di-nucleosomes and at DNA ends and develop quantitative positioning assays to reveal common and distinct features of shaping chromatin in different species. We also explore cryo-EM as tool towards revealing distinct steps the chemo-mechanical remodelling reactions. The proposed research will help derive fundamental molecular principles underlying the modelling of the nucleosome landscape.