Structure of the human inner kinetochore CCAN complex and its significance for human centromere organization

Centromeres are specialized chromosome loci that seed the kinetochore, a large protein complex that effects chromosome segregation. A 16-subunit complex, the constitutive centromere associated network (CCAN), connects between the specialized centromeric chromatin, marked by the histone H3 variant CENP-A, and the spindle-binding moiety of the kinetochore. Here, we report a cryo-electron microscopy structure of human CCAN. We highlight unique features such as the pseudo GTPase CENP-M and report how a crucial CENP-C motif binds the CENP-LN complex. The CCAN structure has implications for the mechanism of specific recognition of the CENP-A nucleosome. A model consistent with our structure depicts the CENP-C-bound nucleosome as connected to the CCAN through extended, flexible regions of CENP-C. An alternative model identifies both CENP-C and CENP-N as specificity determinants but requires CENP-N to bind CENP-A in a mode distinct from the classical nucleosome octamer. [Display omitted] •A cryo-EM structure of the CCAN is reported•The structure rationalizes relative positions and roles of the 16 CCAN subunits•The CCAN core is shown to prefer naked DNA to CENP-A nucleosomes•Several possible models of organization of centromeric chromatin are discussed The centromere is a specialized chromosome locus that seeds the kinetochore, a macromolecular complex that promotes chromosome segregation. Pesenti, Raisch et al. report the structure of the constitutive centromere-associated network (CCAN), a multi-subunit assembly that surrounds CENP-A/CenH3, the centromere’s epigenetic marker. The structure raises fundamental new questions on centromere organization.