ИСТИНА

Nucleosomes are elementary units of chromatin, comprising anoctamer of histone proteins (consisting of two pairs of H3-H4and H2A-H2B histone dimers) which wraps around 150 basepairs of DNA in a left-handed superhelix. While compacting the DNA, nucleosomes remain actively involved in the processes of transcription, DNA replication, repair and provide basis for the epigenetic markup of the genome through the incorporation of histone variants and post-translational modifications. It is knownthat nucleosomes are inherently dynamic structures that mayunwrap DNA or loose certain histone dimers. However, recentfindings suggest that the fine plasticity of the histone octameritself as well as of the individual histone dimers is of key impor-tance for the interaction of nucleosomes with chromatin proteinscomplexes such as nucleosome remodelers. For example, incorpo-ration of disulfide bonds within the histone dimers alters theremodeling process. Motivated by these findings we aimed atdeciphering the various internal motions within the nucleosomecore using molecular dynamics (MD) simulations. We performedMD simulations of a complete nucleosome core particle, a his-tone H3-H4 tetramer, and individual histone dimers as well as the said systems incorporating different mutations. The metady-namics simulations approach was used to explore the systems’behavior along the select collective variables. Particularly theplasticity of the tetrasome structure was explored with respect tothe deformation of the DNA, which resembles DNA stretchingor supercoiling. Using principal component analysis we revealeda number of internal motion modes within the histone dimers,which include long alpha 2 helix bending. Overall our findingscontribute to the understanding of the nucleosome as an inter-nally dynamic entity with implications for functional interactionswith other chromatin proteins. This work was supported by Russian Science Foundation Grant No. 18-74-10006.