Krasilnikov O V, Capistrano M P, Yuldasheva L N, Nogueira R A
Laboratory of Molecular Physiology, Institute of Physiology and Biophysics, 700095 Tashkent, Uzbekistan.
J Membr Biol. 1997 Mar 15;156(2):157-72. doi: 10.1007/s002329900198.
Replacement of an amino acid residue at position 130 -Gly by Cys- in the primary structure of Staphylococcus aureus alpha-toxin decreases the single-channel conductance induced by the toxin in planar lipid bilayers. Concomitantly, the pH value at which the channel becomes unable to discriminate between Cl- and K+ ions is also decreased. By contrast, the pH dependence of the efficiency of the mutant toxin to form ion channels in lipid bilayers was unchanged (maximum efficiency at pH 5.5-6.0). The asymmetry and nonlinearity of the current-voltage characteristics of the channel were increased by the point mutation but the diameter of the water pore induced by the mutant toxin, evaluated in lipid bilayers and in erythrocyte membranes, was found to be indistinguishable from that formed by wild-type toxin and equal to 2.4-2.6 nm. Alterations at the "trans mouth" were found to be responsible for all observed changes of the channel properties. This mouth is situated close to the surface of the second leaflet of a bilayer lipid membrane. The data obtained allows us to propose that the region around residue 130 in fact determines the main features of the ST-channel and takes part in the formation of the trans entrance of the channel.
在金黄色葡萄球菌α-毒素一级结构中，将第130位的氨基酸残基（甘氨酸）替换为半胱氨酸，会降低该毒素在平面脂质双分子层中诱导的单通道电导。与此同时，通道无法区分氯离子和钾离子时的pH值也会降低。相比之下，突变毒素在脂质双分子层中形成离子通道的效率对pH的依赖性并未改变（在pH 5.5 - 6.0时效率最高）。点突变增加了通道电流-电压特性的不对称性和非线性，但在脂质双分子层和红细胞膜中评估发现，突变毒素诱导形成的水孔直径与野生型毒素形成的水孔直径没有区别，均为2.4 - 2.6纳米。研究发现，“跨膜口”处的改变是导致通道特性所有观察到变化 的原因。这个口位于双层脂质膜第二个小叶的表面附近。所获得的数据使我们能够提出，第130位残基周围的区域实际上决定了ST通道的主要特征，并参与了通道跨膜入口的形成。
