Departamento de Bioquímica y Biología Molecular, Universidad Complutense, 28040 Madrid, Spain.
Biochemistry, Faculty of Science and Engineering, Åbo Akademi University, 20520 Turku, Finland.
Biochemistry. 2021 Feb 2;60(4):314-323. doi: 10.1021/acs.biochem.0c00840. Epub 2021 Jan 14.
Sticholysins are pore-forming toxins produced by sea anemones that are members of the actinoporin family. They exert their activity by forming pores on membranes, provided they have sphingomyelin. To assemble into pores, specific recognition, binding, and oligomerization are required. While recognition and binding have been extensively studied, delving into the oligomerization process and the stoichiometry of the pores has been more difficult. Here, we present evidence that these toxins are capable of oligomerizing in solution and suggesting that the interaction of sticholysin II (StnII) with its isoform sticholysin I (StnI) is stronger than that of StnI with itself. We also show that the stoichiometry of the final, thermodynamically stable StnI pores is, at least, heptameric. Furthermore, our results indicate that this association maintains its oligomerization number when StnII is included, indicating that the stoichiometry of StnII is also of that order, and not tetrameric, as previously thought. These results are compatible with the stoichiometry observed for the crystallized pore of FraC, another very similar actinoporin produced by a different sea anemone species. Our results also indicate that the stoichiometry of actinoporin pores in equilibrium is conserved regardless of the particular composition of a given pore ensemble, which we have shown for mixed sticholysin pores.
海葵毒素是一类由海葵产生的具有孔道形成活性的蛋白毒素，属于动质素超家族。这类毒素通过在含有神经鞘磷脂的膜上形成孔道来发挥作用。为了组装成孔道，需要特定的识别、结合和寡聚化。虽然识别和结合已经得到了广泛的研究，但深入研究寡聚化过程和孔道的化学计量学更为困难。在这里，我们提供的证据表明，这些毒素能够在溶液中寡聚化，并表明 StnII（海葵毒素 II）与其同工型 StnI（海葵毒素 I）的相互作用强于 StnI 与其自身的相互作用。我们还表明，最终热力学稳定的 StnI 孔道的化学计量学至少为七聚体。此外，我们的结果表明，当包含 StnII 时，这种关联保持其寡聚化数量，表明 StnII 的化学计量学也处于该数量级，而不是以前认为的四聚体。这些结果与另一种不同海葵物种产生的非常相似的动质素 FraC 结晶孔道的观察到的化学计量学一致。我们的结果还表明，无论特定孔道组合的特定组成如何，平衡状态下动质素孔道的化学计量学都是保守的，我们已经在混合海葵毒素孔道中证明了这一点。
