ANTHRAX TOXIN PROTECTIVE ANTIGEN - LOW-PH-INDUCED HYDROPHOBICITY AND CHANNEL FORMATION IN LIPOSOMES
ANTHRAX TOXIN PROTECTIVE ANTIGEN - LOW-PH-INDUCED HYDROPHOBICITY AND CHANNEL FORMATION IN LIPOSOMES
复制标题
DOI：
10.1111/j.1365-2958.1991.tb00796.x
复制
发表时间：
1991-06-01
影响因子：
3.6
通讯作者：
COLLIER, RJ
中科院分区：
文献类型：
--
作者：
KOEHLER, TM;COLLIER, RJ
为了探讨炭疽毒素的保护性抗原（PA）成分在毒素进入动物细胞中的作用，我们检测了完整的和胰蛋白酶切割形式的炭疽毒素在不同pH值下的膜通道形成特性和疏水性。在中性pH下，这两种形式都不会引起单层脂质囊泡中的K+释放。然而，在pH值低于6.0时，加入有缺口的PA（PA(N)）或PA的63 kDa色氨酸片段（PA63）后，K+迅速释放，这与毒素进入过程有关。在相同条件下，完整的PA仅表现出微弱的通道形成活性，而互补色氨酸片段PA20则没有这种活性。PA和PA63在酸性pH值下均表现出增强的疏水性，但PA63的增强更大，pH阈值更高。我们的研究结果表明，从完整的PA中蛋白水解去除PA20使残留蛋白PA63在轻度酸性pH值下采用一种构象，使其易于插入并在膜中形成通道。因此，内吞囊泡内的酸性条件可能触发PA63的膜插入，这反过来促进结扎效应部分、水肿因子或致死因子穿过囊泡膜进入细胞质。
To probe the role of the protective antigen (PA) component of anthrax toxin in toxin entry into animals cells, we examined the membrane channel-forming properties and hydrophobicity of intact and trypsincleaved forms of the protein at various pH values. At neutral pH neither form caused release of entrapped K+ from unilamellar lipid vesicles. At pH values below 6.0, however, K+ was rapidly released upon addition of either the nicked PA (PA(N)) or the 63 kDa tryptic fragment of PA (PA63), which has been implicated in the toxin entry process. Under the same conditions intact PA exhibited only weak channel-forming activity, and PA20, the complementary tryptic fragment, showed no such activity. Both PA and PA63 exhibited enhanced hydrophobicity at acidic pH values, but the enhancement was greater and the pH threshold higher with PA63. Our findings indicate that proteolytic removal of PA20 from intact PA enables the residual protein, PA63, to adopt a conformation at mildly acidic pH values that permits it to insert readily and form channels in membranes. Thus acidic conditions within endocytic vesicles may trigger membrane insertion of PA63, which in turn promotes translocation of ligated effector moieties, edema factor or lethal factor, across the vesicle membrane into the cytosol.