Abstract
Centromeres are microtubule attachment sites on chromosomes defined by the enrichment of histone variant CENP‐A‐containing nucleosomes. To preserve centromere identity, CENP‐A must be escorted to centromeres by a CENP‐A‐specific chaperone for deposition. Despite this essential requirement, many eukaryotes differ in the composition of players involved in centromere maintenance, highlighting the plasticity of this process. In humans, CENP‐A recognition and centromere targeting are achieved by HJURP and the Mis18 complex, respectively. Using X‐ray crystallography, we here show how Drosophila CAL1, an evolutionarily distinct CENP‐A histone chaperone, binds both CENP‐A and the centromere receptor CENP‐C without the requirement for the Mis18 complex. While an N‐terminal CAL1 fragment wraps around CENP‐A/H4 through multiple physical contacts, a C‐terminal CAL1 fragment directly binds a CENP‐C cupin domain dimer. Although divergent at the primary structure level, CAL1 thus binds CENP‐A/H4 using evolutionarily conserved and adaptive structural principles. The CAL1 binding site on CENP‐C is strategically positioned near the cupin dimerisation interface, restricting binding to just one CAL1 molecule per CENP‐C dimer. Overall, by demonstrating how CAL1 binds CENP‐A/H4 and CENP‐C, we provide key insights into the minimalistic principles underlying centromere maintenance.
Highlights
Centromeres are specialised chromosomal regions that act as a platform for the assembly of kinetochores, the microtubule anchoring sites essential for chromosome segregation during mitosis and meiosis (Musacchio & Desai, 2017)
Secondary structure prediction analysis indicated that CAL1 is likely to be a predominantly unstructured protein, it includes an N-terminal domain spanning amino acid residues 1–200 predicted to fold into a helices (Fig EV1A and B)
Limited proteolysis experiments performed on CAL11–160–CENP-A101–225–H4 complex using different proteases suggested that a CENP-A fragment containing aa 144–255 (CENPA144–255) is sufficient to interact with CAL1 and H4
Summary
Centromeres are specialised chromosomal regions that act as a platform for the assembly of kinetochores, the microtubule anchoring sites essential for chromosome segregation during mitosis and meiosis (Musacchio & Desai, 2017). A central player in this process is the CENP-A-specific chaperone HJURP in human and its homologue Scm in fungi (Kato et al, 2007; Foltz et al, 2009; Pidoux et al, 2009; Sanchez-Pulido et al, 2009; Dunleavy et al, 2011) Both HJURP and Scm can bind the CENP-A–histone H4 (CENP-A/H4) heterodimer in its pre-nucleosomal form, and these complexes are targeted to centromeres by the Mis complex (Fujita et al, 2007; Moree et al, 2011; Dambacher et al, 2012; Hayashi et al, 2014; McKinley & Cheeseman, 2014; Nardi et al, 2016; Stellfox et al, 2016; French et al, 2017; Hori et al, 2017).
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