Structural basis for centromere maintenance by Drosophila CENP-A chaperone CAL1

Centromeres are microtubule attachment sites on chromosomes defined by the enrichment of 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 is achieved by HJURP and the Mis18 complex, respectively. Here, using crystal structures we show how Drosophila CAL1, an evolutionarily distinct CENP-A chaperone, binds both CENP-A and the centromere receptor CENP-C without the requirement of the Mis18 complex: while the N-terminal CAL1 fragment wraps around CENP-A/H4 through multiple physical contacts, the C-terminal CAL1 fragment directly binds CENP-C cupin dimer. CAL1, though divergent at the primary structure, binds CENP-A/H4 using evolutionarily conserved and adaptive structural principles. The CAL1 binding site on CENP-C strategically lies near the cupin dimerisation interface restricting just one CAL1 binding per CENP-C dimer. Overall, by demonstrating how CAL1 binds CENPA/H4 and CENP-C, we provide key insights into the minimalistic principles underlying centromere maintenance.