Caaveiro J M, Echabe I, Gutiérrez-Aguirre I, Nieva J L, Arrondo J L, González-Mañas J M
Unidad de Biofísica (CSIC-UPV/EHU) and Departamento de Bioquímica y Biología Molecular, Universidad del País Vasco, Apartado 644, 48080 Bilbao, Spain.
Biophys J. 2001 Mar;80(3):1343-53. doi: 10.1016/S0006-3495(01)76107-3.
Equinatoxin II is a 179-amino-acid pore-forming protein isolated from the venom of the sea anemone Actinia equina. Large unilamellar vesicles and lipid monolayers of different lipid compositions have been used to study its interaction with membranes. The critical pressure for insertion is the same in monolayers made of phosphatidylcholine or sphingomyelin (approximately 26 mN m(-1)) and explains why the permeabilization of large unilamellar vesicles by equinatoxin II with these lipid compositions is null or moderate. In phosphatidylcholine-sphingomyelin (1:1) monolayers, the critical pressure is higher (approximately 33 mN m(-1)), thus permitting the insertion of equinatoxin II in large unilamellar vesicles, a process that is accompanied by major conformational changes. In the presence of vesicles made of phosphatidylcholine, a fraction of the protein molecules remains associated with the membranes. This interaction is fully reversible, does not involve major conformational changes, and is governed by the high affinity for membrane interfaces of the protein region comprising amino acids 101-120. We conclude that although the presence of sphingomyelin within the membrane creates conditions for irreversible insertion and pore formation, this lipid is not essential for the initial partitioning event, and its role as a specific receptor for the toxin is not so clear-cut.
海葵毒素II是一种从海葵（Actinia equina）毒液中分离出的由179个氨基酸组成的成孔蛋白。不同脂质组成的大单层囊泡和脂质单分子层已被用于研究其与膜的相互作用。在由磷脂酰胆碱或鞘磷脂制成的单分子层中，插入的临界压力相同（约26 mN m(-1)），这解释了为什么海葵毒素II对具有这些脂质组成的大单层囊泡的通透作用为零或适中。在磷脂酰胆碱 - 鞘磷脂（1:1）单分子层中，临界压力更高（约33 mN m(-1)），从而允许海葵毒素II插入大单层囊泡，这一过程伴随着主要的构象变化。在存在由磷脂酰胆碱制成的囊泡的情况下，一部分蛋白质分子仍与膜结合。这种相互作用是完全可逆的，不涉及主要的构象变化，并且由包含氨基酸101 - 120的蛋白质区域对膜界面的高亲和力所控制。我们得出结论，尽管膜内鞘磷脂的存在为不可逆插入和孔形成创造了条件，但这种脂质对于初始分配事件并非必不可少，并且其作为毒素特异性受体的作用并不那么明确。
