Analysis of lanthanide-induced conformational change of the C-terminal domain on centrin.

Centrin, an EF-hand calcium-binding protein with high homology to calmodulin (CaM), is an essential component of microtubule-organizing center (MTOC). Lanthanide (Ln) ions can improve the stability, increase the amount and enhance the orderliness of microtubules, which are components of cytoskeleton. In order to investigate the structural basis of Ln ions on enhancing orderliness of microtubules, we characterized the binding properties of Ln ions with the isolated C-terminal domain of the Euplotes centrin (C-EoCen). Results suggested that Ln ions may occupy the canonical Ca(2+) binding sites on C-EoCen with middle affinity. Near- and far-UV CD spectra of C-EoCen displayed pronounced differences before and after additing Ln ions. The asymmetry of microenvironments of Phe on C-EoCen was changed. Using 2-p-toluidinylnaphthalene-6- sulfonate (TNS) as probe, Ln ions induced C-EoCen to undergo conformational changes from closed state to open state, resulting in exposing hydrophobic patches to external environments. Ln ions have more obvious effect on the conformation of centrin than Ca(2+). The differences found in the interactions of centrin binding with Ln ions/Ca(2+) maybe provide some insights for structural basis of centrin functions in vivo.