Centrins are calcium (Ca²⁺)-binding proteins that have been implicated in several regulatory functions. In the protozoan parasite Toxoplasma gondii, the causative agent of toxoplasmosis, three isoforms of centrin have been identified. While increasing information is now available that links the function of centrins with defined parasite biological processes, knowledge is still limited on the metal-binding and structural properties of these proteins. Herein, using biophysical and structural approaches, we explored the Ca²⁺ binding abilities and the subsequent effects of Ca²⁺ on the structure of a conserved (TgCEN1) and a more divergent (TgCEN2) centrin isoform from T. gondii. Our data showed that TgCEN1 and TgCEN2 possess diverse molecular features, suggesting that they play nonredundant roles in parasite physiology. TgCEN1 binds two Ca²⁺ ions with high/medium affinity, while TgCEN2 binds one Ca²⁺ with low affinity. TgCEN1 undergoes significant Ca²⁺-dependent conformational changes that expose hydrophobic patches, supporting a role as a Ca²⁺ sensor in toxoplasma. In contrast, Ca²⁺ binding has a subtle influence on conformational features of TgCEN2 without resulting in hydrophobic exposure, suggesting a different Ca²⁺ relay mode for this isoform. Furthermore, TgCEN1 displays a Ca²⁺-dependent ability to self-assemble, while TgCEN2 did not. We discuss our findings in the context of Ca²⁺ signaling in toxoplasma.

中文翻译：

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弓形虫两种 Centrin 亚型的独特钙结合和结构特性。


中心蛋白是钙 (Ca ²⁺ ) 结合蛋白，与多种调节功能有关。在原生动物寄生虫弓形虫（弓形虫病的病原体）中，已鉴定出中心蛋白的三种亚型。虽然现在有越来越多的信息将中心蛋白的功能与确定的寄生虫生物过程联系起来，但对这些蛋白质的金属结合和结构特性的了解仍然有限。在此，我们利用生物物理和结构方法，探讨了 Ca ²⁺结合能力以及 Ca ²⁺对弓形虫保守型 (TgCEN1) 和更趋异型 (TgCEN2) 中心蛋白亚型结构的后续影响。我们的数据显示 TgCEN1 和 TgCEN2 具有不同的分子特征，表明它们在寄生虫生理学中发挥着非冗余的作用。 TgCEN1 以高/中亲和力结合两个 Ca ²⁺离子，而 TgCEN2 以低亲和力结合一个 Ca ²⁺离子。 TgCEN1 经历显着的 Ca ²⁺依赖性构象变化，暴露疏水斑块，支持在弓形虫中作为 Ca ²⁺传感器的作用。相比之下，Ca ²⁺结合对 TgCEN2 的构象特征有微妙的影响，而不会导致疏水性暴露，表明该异构体具有不同的 Ca ²⁺中继模式。此外，TgCEN1 显示出 Ca ²⁺依赖性自组装能力，而 TgCEN2 则不然。我们在弓形虫中 Ca ²⁺信号传导的背景下讨论我们的发现。