Poster abstracts

Poster number 120 submitted by Zach Shaffer

The structural and behavioral characterization of histone protein H2A in nucleosome arrays using solid-state NMR

Zach M. Shaffer (Ohio State Biochemistry Program), Motilal Uttarkabat (Biophysics Graduate Program), Trent W. Franks (Department of Chemistry and Biochemistry), Michael G. Poirier, Christopher P. Jaroniec (Department of Chemistry and Biochemistry)

Abstract:
Chromatin is composed of individual nucleosomes arranged periodically along the length of genomic DNA in eukaryotic cells. Each nucleosome consists of DNA wrapped around octamers of histone proteins H2A, H2B, H3 and H4. Each histone consists of a primarily &alpha-helical rigid core and flexible N-terminal tails that extend out from the core1. The histones are largely positively charged, but surface-exposed residues E56, E61, E64, D90, E91, and E92 of H2A, as well as residues E102, and E110 of H2B comprise a negatively charged region known as the acidic patch, which plays an important role in global chromatin architecture2. Much work has been done using this technique to study mono-nucleosomes, but analogous study of nucleosomes in extended arrays remains lacking due to their size. Magic angle spinning solid-state nuclear magnetic resonance (NMR) spectroscopy is particularly advantageous for studying biological complexes like chromatin because it allows measurements of both the local structure and dynamic behavior of very large biomolecular model systems with atomic-level resolution. Here, I use solid-state NMR to study H2A in 16-mer nucleosome arrays. I used multidimensional 1H-detected experiments to make a near-complete resonance assignment of H2A rigid core residues, as well as the tails. A chemical shift comparison between H2A in a 16-mer nucleosome array with an analogous study of H2A in mono-nucleosomes by Xiang et al.3 show significant chemical shift perturbations with residues Y39, N68, H82, and L83, suggesting structural differences within the histone octamer core brought about by the specific higher order compaction of the 16-mer array. Further experiments probing microsecond-milisecond timescale dynamics of the rigid core will show behavior of H2A within the nucleosome array.

References:
(1)Li, B.; Carey, M.; Workman, J. L. The Role of Chromatin during Transcription. Cell 2007, 128 (4), 707719. https://doi.org/10.1016/j.cell.2007.01.015.
(2)Kalashnikova, A. A.; Porter-Goff, M. E.; Muthurajan, U. M.; Luger, K.; Hansen, J. C. The Role of the Nucleosome Acidic Patch in Modulating Higher Order Chromatin Structure. J. R. Soc. Interface 2013, 10 (82), 20121022. https://doi.org/10.1098/rsif.2012.1022.
(3)Xiang, S.; le Paige, U. B.; Horn, V.; Houben, K.; Baldus, M.; van Ingen, H. Site-Specific Studies of Nucleosome Interactions by Solid-State NMR Spectroscopy. Angew. Chem. Int. Ed. 2018, 57 (17), 45714575. https://doi.org/10.1002/anie.201713158.

Keywords: Chromatin, nucleosome array, solid-state NMR