CENP‐C unwraps the human CENP‐A nucleosome through the H2A C‐terminal tail

Abstract

Centromeres are defined epigenetically by nucleosomes containing the histone H3 variant CENP‐A, upon which the constitutive centromere‐associated network of proteins ( CCAN) is built. CENP‐C is considered to be a central organizer of the CCAN. We provide new molecular insights into the structure of human CENP‐A nucleosomes, in isolation and in complex with the CENP‐C central region ( CENP‐ C ^CR ), the main CENP‐A binding module of human CENP‐C. We establish that the short αN helix of CENP‐A promotes DNA flexibility at the nucleosome ends, independently of the sequence it wraps. Furthermore, we show that, in vitro, two regions of human CENP‐C ( CENP‐ C ^CR and CENP‐C ^motif) both bind exclusively to the CENP‐A nucleosome. We find CENP‐ C ^CR to bind with high affinity due to an extended hydrophobic area made up of CENP‐ A ^{V 532} and CENP‐ A ^{V 533}. Importantly, we identify two key conformational changes within the CENP‐A nucleosome upon CENP‐C binding. First, the loose DNA wrapping of CENP‐A nucleosomes is further exacerbated, through destabilization of the H2A C‐terminal tail. Second, CENP‐ C ^CR rigidifies the N‐terminal tail of H4 in the conformation favoring H4 ^K20 monomethylation, essential for a functional centromere.