Centrins contain four potential Ca2+ binding sites, known as EF-hands, and have essential functions in centrosome duplication and filament contraction. Here we report that centrins from yeast, green algae, and humans bound with high affinity to a peptide of the yeast centrosomal component Kar1p. Interestingly, centrin binding was regulated by physiological relevant changes in [Ca2+], and this Ca2+ dependence was influenced by acidic amino acids within the Kar1p peptide, which also prevented efficient binding of the related yeast calmodulin. However, a hybrid protein with the third and fourth EF-hands from the yeast centrin Cdc31p and the amino-terminal half from yeast calmodulin behaved more like Cdc31p, indicating that the carboxyl-terminal half of Cdc31p influences binding specificity. Besides Kar1p, centrins bound to a yeast calmodulin binding site, explaining the dosage-dependent suppression of a calmodulin mutant by CDC31. Consistent with an essential role of Ca2+ for centrin functions, mutations in the first or the fourth EF-hands of Cdc31p, impairing the Ca2+-induced conformational change of Cdc31p, resulted in nonfunctional proteins in vivo. Our results suggest that centrins are involved in Ca2+ signaling, likely by influencing the properties of target proteins in response to changes in [Ca2+].
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