Bakás L, Ostolaza H, Vaz W L, Goñi F M
Departamento de Bioquímica, Universidad del País Vasco, Bilbao, Spain.
Biophys J. 1996 Oct;71(4):1869-76. doi: 10.1016/S0006-3495(96)79386-4.
Alpha-Hemolysin is an extracellular protein toxin (107 kDa) produced by some pathogenic strains of Escherichia coli. Although stable in aqueous medium, it can bind to lipid bilayers and produce membrane disruption in model and cell membranes. Previous studies had shown that toxin binding to the bilayer did not always lead to membrane lysis. In this paper, we find that alpha-hemolysin may bind the membranes in at least two ways, a reversible adsorption and an irreversible insertion. Reversibility is detected by the ability of liposome-bound toxin to induce hemolysis of added horse erythrocytes; insertion is accompanied by an increase in the protein intrinsic fluorescence. Toxin insertion does not necessarily lead to membrane lysis. Studies of alpha-hemolysin insertion into bilayers formed from a variety of single phospholipids, or binary mixtures of phospholipids, or of phospholipid and cholesterol, reveal that irreversible insertion is favored by fluid over gel states, by low over high cholesterol concentrations, by disordered liquid phases over gel or ordered liquid phases, and by gel over ordered liquid phases. These results are relevant to the mechanism of action of alpha-hemolysin and provide new insights into the membrane insertion of large proteins.
α-溶血素是由某些致病性大肠杆菌菌株产生的一种细胞外蛋白质毒素（107 kDa）。尽管它在水性介质中稳定，但能与脂质双层结合，并在模型膜和细胞膜中造成膜破坏。先前的研究表明，毒素与双层的结合并不总是导致膜裂解。在本文中，我们发现α-溶血素可能至少通过两种方式与膜结合，一种是可逆吸附，另一种是不可逆插入。通过脂质体结合毒素诱导添加的马红细胞溶血的能力来检测可逆性；插入伴随着蛋白质固有荧光的增加。毒素插入不一定导致膜裂解。对α-溶血素插入由各种单一磷脂、磷脂二元混合物或磷脂与胆固醇形成的双层的研究表明，流体状态比凝胶状态更有利于不可逆插入，低胆固醇浓度比高胆固醇浓度更有利于不可逆插入，无序液相比凝胶或有序液相更有利于不可逆插入，凝胶相比有序液相更有利于不可逆插入。这些结果与α-溶血素的作用机制相关，并为大型蛋白质的膜插入提供了新的见解。
