Biophysical Society Thematic Meeting| Les Houches 2019

Multiscale Modeling of Chromatin: Bridging Experiment with Theory

Wednesday Speaker Abstracts

STRUCTURE AND DYNAMICS OF THE TELOMERIC NUCLEOSOME AND CHROMATIN Lars Nordenskiöld 1 Nanyang Technological University, School of Biological Sciences, Singapore, South-West, Singapore Eukaryotic genomic DNA is condensed into chromatin: 146bp DNA wraps around the histone octamer (HO) comprising two copies each of the core histones H2A, H2B, H3 and H4 forming the nucleosome core particle (NCP). A string of nucleosomes folds into the so-called called “30nm” chromatin fibre, which compacts into metaphase chromosomes. Human telomeres constitute the protective structure at the end of the chromosomes with repetitive TTAGGG sequences that are about 10kbp. Little is known about the consequences of this unique sequence for chromatin structural and dynamic properties. Although it is established that telomeric DNA is packaged in chromatin with an unusually short (157 bp) nucleosome repeat length (NRL) and can form nucleosomes and chromatin, almost nothing is known about the telomeric nucleosome core and telomeric chromatin structure at the detailed molecular level. We have characterised the telomeric human HO 145 bp DNA NCP (Telo-NCP), using biophysical methods and determined its structure at 2.1 Å resolution with X-ray crystallography. Although the structure is largely similar to the well-known published atomic resolution NCP structures, several differences can be identified, e.g. DNA stretching on the Telo-NCP is different from that of the “601” (high-affinity nucleosome positioning sequence) and alpha satellite NCPs of the same length. We have designed and prepared 20×157 bp telomeric DNA template repeats, reconstituted these with human HO and performed characterisation of the structural and dynamic properties of the telomeric chromatin fibres with EM, solid-state NMR and single molecule magnetic tweezer experiments. Telomeric chromatin fibres are considerably more homogeneous than corresponding 157 bp repeat fibres reconstituted from 601-DNA array templates. However, the structural and dynamic properties of individual telomeric arrays saturated with 20 nucleosomes, appear similar to equivalent 601 chromatin fibres under the influence of force in single molecule pulling experiment.

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