Jeyaprakash lab paper featured in EMBO Journal. Authors Image Medina-Pritchard, B., Lazou, V., Zou, J., Byron, O., Abad, M.A., Rappsilber, J., Heun, P., and Jeyaprakash, A.A. Summary of Paper by Lori Koch In eukaryotic cells, DNA is packaged into chromosomes by wrapping DNA around histone proteins to form nucleosomes. To be inherited properly, every chromosome must have a region called the centromere where the nucleosomes contain a specialised histone protein called CENP-A. In human cells, the CENP-A protein is inserted in the correct position by a CENP-A specific chaperone HJURP, whose centromere targeting is controlled by the Mis18 protein complex. Interestingly, flies have an evolutionarily distinct CENP-A chaperone protein, CAL1, that seems to combine the functions of human HJURP and Mis18. However, exactly how CAL1 interacts with CENP-A and targets it to the centromere simultaneously was unclear. In their recent study in EMBO Journal, researchers from the Jeyaprakash (JP) lab in collaboration with the Heun lab present x-ray crystal structures of CAL1 in complex with CENP-A/H4 and CAL1 bound to its centromere receptor CENP-C. The researchers obtained two crystal structures of the N-terminus of fly CAL1 in complex with a CENP-A/H4 heterodimer at 3.5 and 4.4 Angstrom resolution. Consistent with previous findings, the complex was a 1:1:1 hetero-trimer. Specifically, they determined that CAL1 amino acids W22 and F29 are crucial for CENP-A/H4 binding by performing in vitro pull-down assays. The Heun lab confirmed the importance of these residues in vivo by performing co-localization experiments where they measured the recruitment of CAL1 to CENP-A tethered to an ectopic locus in human and Drosophila cells. Next, they aimed to determine the structural basis for the centromere association of CAL1. It was known that CAL1 binds to the conserved centromere protein CENP-C but the structure was unknown. Thus, the authors determined a crystal structure of the CAL1 C-terminus in complex with the C-terminus of CENP-C (cupin domain) at 2.3 Angstrom resolution. They found that CAL1 binds the CENP-C cupin domain at a site close to the cupin dimerization interface. This mode of binding restricts association of just one CAL1 per CENP-C dimer. Structure-guided mutations at the binding interface disrupted complex formation in vitro and also prevented recruitment of CAL1 to CENP-C in human and fly cells. Overall, their study presents the structural basis for how CAL1 recognises and targets CENP-A to centromeres in flies and this may inform future studies on the minimal requirements for centromere maintenance through successive generations in diverse organisms. Related links Journal Link Arulanandan Lab Website This article was published on 2024-06-17
