BINDING OF CENTRINS AND YEAST CALMODULIN TO SYNTHETIC PEPTIDES CORRESPONDING TO BINDING-SITES IN THE SPINDLE POLE BODY COMPONENTS KAR1P ANDSPC110P

Centrins contain four potential Ca2+ binding sites, known as EF-hands, and have essential functions in centrosome duplication and filament c ontraction. Here we report that centrins hom yeast, green algae, and h umans bound with high affinity to a peptide of the yeast centrosomal c omponent Kar1p, Interestingly, centrin binding was regulated by physio logical relevant changes in [Ca2+], and this Ca2+ dependence was influ enced by acidic amino acids within the Kar1p peptide, which also preve nted efficient binding of the related yeast calmodulin, However, a hyb rid 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 infl uences binding specificity, Besides Kar1p, centrins bound to a yeast c almodulin binding site, explaining the dosage-dependent suppression of a calmodulin mutant by CDC31. Consistent with an essential role of Ca 2+ for centrin functions, mutations in the first or the fourth EF-hand s of Cdc31p, impairing the Ca2+-induced conformational change of Cdc31 p, resulted in nonfunctional proteins in vice, Our results suggest tha t centrins are involved in Ca2+ signaling likely by influencing the pr operties of target proteins in response to changes in [Ca2+].