EFFECT OF PH ON THE CONFORMATION OF DIPHTHERIA-TOXIN AND ITS IMPLICATIONS FOR MEMBRANE PENETRATION
EFFECT OF PH ON THE CONFORMATION OF DIPHTHERIA-TOXIN AND ITS IMPLICATIONS FOR MEMBRANE PENETRATION
复制标题
DOI：
10.1021/bi00341a027
复制
发表时间：
1985-01-01
期刊：
影响因子：
2.9
通讯作者：
LONDON, E
中科院分区：
文献类型：
--
作者：
BLEWITT, MG;CHUNG, LA;LONDON, E
已经检查了pH值引发的白喉毒素构象的变化以及在过渡pH值上下的毒素的物理性质。暴露于低pH值环境中。5度，23度。C, .ltoreq。37度时5.3度。C)引起毒素构象的快速变化（t1/2 < 30秒）；转变发生在一个狭窄的pH范围内（0.2单位）。在过渡pH值以下，埋藏的色氨酸暴露出来，有毒物质变得疏水，与洗涤剂紧密结合。在低pH下观察到聚集，可能是由于这种极端的疏水性。圆二色性和荧光性质表明低ph构象没有广泛展开。因此，毒素在低pH值下“打开”，而不会成为随机线圈。构象的变化部分是不可逆的，不可逆的程度与聚集的程度相当。二硫键的减少不会增加中性pH下的疏水性。此外，毒素的结构变体（单体或二聚体，与ApUp结合或游离，亚基之间有缺口或完整）在中性pH下都不疏水，或在过渡pH上有显著差异。因此，这些因素不能模拟低ph的影响。这些观察结果与酸性细胞器膜渗透过程中ph触发的变化的功能作用是一致的。毒素可能已经适应了类似于部分变性的构象变化，在功能中起关键作用。简要讨论了ph敏感相互作用的可能性质和聚集效应。
The pH-triggered change in diphthera toxin conformation and the physical properties of the toxin above and below the transition pH have been examined. Exposure to low pH (.ltoreq. 5 at 23.degree. C, .ltoreq. 5.3 at 37.degree. C) triggers a rapid (t1/2 < 30 s) change in toxin conformation; the transition occurs over a narrow pH range (0.2 unit). Below the transition pH, buried tryptophans become exposed, and the toxic becomes hydrophobic, binding very tightly to detergent. Aggregation is observed at low pH, probably due to this extreme hydrophobicity. Circular dichroism and fluorescence properties show that the low-pH conformation is not extensively unfolded. Therefore, the toxin "opens" at low pH without becoming a random coil. The conformation change is partly irreversible, and the degree of irreversibility parallels the degree of aggregation. Reduction of the disulfide bonds does not increase hydrophobicity at neutral pH. Furthermore, none of the structural variants of toxin (monomer or dimer, bound to ApUp or free, and nicked between subunits or intact) are hydrophobic at neutral pH or differ in transition pH markedly. Therefore, these factors do not mimic the effect of low pH. These observations are consistent with a functional role for pH-triggered changes during penetration of the membranes of acidic organelles. The toxin may have adapted a conformational change similar to partial denaturation for a critical role in function. The possible nature of the pH-sensitive interactions and the effects of aggregation are discussed briefly.