Cryo-EM Structures of Centromeric Tri-nucleosomes Containing a Central CENP-A Nucleosome

Structure. 2020 Jan 7;28(1):44-53.e4. doi: 10.1016/j.str.2019.10.016. Epub 2019 Nov 8.

Abstract

The histone H3 variant CENP-A is a crucial epigenetic marker for centromere specification. CENP-A forms a characteristic nucleosome and dictates the higher-order configuration of centromeric chromatin. However, little is known about how the CENP-A nucleosome affects the architecture of centromeric chromatin. In this study, we reconstituted tri-nucleosomes mimicking a centromeric nucleosome arrangement containing the CENP-A nucleosome, and determined their 3D structures by cryoelectron microscopy. The H3-CENP-A-H3 tri-nucleosomes adopt an untwisted architecture, with an outward-facing linker DNA path between nucleosomes. This is distinct from the H3-H3-H3 tri-nucleosome architecture, with an inward-facing DNA path. Intriguingly, the untwisted architecture may allow the CENP-A nucleosome to be exposed to the solvent in the condensed chromatin model. These results provide a structural basis for understanding the 3D configuration of CENP-A-containing chromatin, and may explain how centromeric proteins can specifically target the CENP-A nucleosomes buried in robust amounts of H3 nucleosomes in centromeres.

Keywords: CENP-A; centromere; chromatin; cryo-EM; histone variant; nucleosome.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Centromere Protein A / chemistry*
  • Centromere Protein A / metabolism*
  • Cryoelectron Microscopy
  • Histones / chemistry*
  • Histones / metabolism*
  • Humans
  • Models, Molecular
  • Protein Binding
  • Protein Conformation

Substances

  • CENPA protein, human
  • Centromere Protein A
  • Histones