Conformational Plasticity of Centrin 1 from Toxoplasma gondii in Binding to the Centrosomal Protein SFI1

Centrins are calcium (Ca2+)-binding proteins that are involved in many cellular functions including centrosome regulation. A known cellular target of centrins is SFI1, a large centrosomal protein containing multiple repeats that represent centrin-binding motifs. Recently, a protein homologous to yeast and mammalian SFI1, denominated TgSFI1, which shares SFI1-repeat organization, was shown to colocalize at centrosomes with centrin 1 from Toxoplasma gondii (TgCEN1). However, the molecular details of the interaction between TgCEN1 and TgSFI1 remain largely unknown. Herein, combining different biophysical methods, including isothermal titration calorimetry, nuclear magnetic resonance, circular dichroism, and fluorescence spectroscopy, we determined the binding properties of TgCEN1 and its individual N- and C-terminal domains to synthetic peptides derived from distinct repeats of TgSFI1. Overall, our data indicate that the repeats in TgSFI1 constitute binding sites for TgCEN1, but the binding modes of TgCEN1 to the repeats differ appreciably in terms of binding affinity, Ca2+ sensitivity, and lobe-specific interaction. These results suggest that TgCEN1 displays remarkable conformational plasticity, allowing for the distinct repeats in TgSFI1 to possess precise modes of TgCEN1 binding and regulation during Ca2+ sensing, which appears to be crucial for the dynamic association of TgCEN1 with TgSFI1 in the centrosome architecture.

Automated summary

In this study, the binding properties of Centrin 1 and its interaction with the repeats of SFI1 in Toxoplasma gondii were investigated using various biophysical methods. The results showed that the repeats in SFI1 serve as binding sites for Centrin 1, but the binding modes differ in terms of affinity, Ca2+ sensitivity, and lobe-specific interaction. These findings suggest that Centrin 1 exhibits conformational plasticity, allowing for precise binding and regulation with the repeats of SFI1 during Ca2+ sensing, which is crucial for the dynamic association of Centrin 1 with SFI1 in centrosome architecture.