The small calmodulin-like family protein centrin 2 binds Ca2+ through its four EF-hand domains. Centrin 2 localises to the lumen of the centriole as part of the centrosome and the cilium, but is also part of the xeroderma pigmentosum group C complex, which ensures nucleotide excision repair (NER) after DNA lesion. In their study (Khouj et al., 2019), Ciaran Morrison and colleagues performed a mutagenesis approach to clarify the structural basis for the distinct cellular roles of centrin 2. The authors mutated the EF-hand domains – rendering them unable to bind Ca2+ – and monitored centriole localisation and NER. Whereas protein mutant for all four EF-hand domains was able to rescue the UV sensitivity of centrin 2-deficient cells, with such cells becoming proficient in NER, both centrosomal localisation and primary ciliogenesis were defective with these mutants. In addition, the authors find that the localisation of centrin 2 was impaired when two or more EF-hand domains were mutated and the retention and localisation of crucial centriolar proteins is affected. Taken together, these results establish a structural separation of centrin 2 functions: whereas the Ca2+-binding EF-hand domains of centrin 2 are not needed for efficient NER, they are required for protein interactions at the centriole and ciliogenesis. Deficiencies in cilia formation are linked to human disorders called ciliopathies, and this work contributes to the dissection of the underlying causes and protein networks of aberrant ciliogenesis.
