Similarity of the conformation of diphtheria toxin at high temperature to that in the membrane-penetrating low-pH state.
Similarity of the conformation of diphtheria toxin at high temperature to that in the membrane-penetrating low-pH state.
复制标题
白喉毒素在高温下的构象与透膜低pH状态下的构象相似。
DOI：
10.1073/pnas.83.7.2002
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发表时间：
1986
影响因子：
11.1
通讯作者：
London,E
中科院分区：
文献类型：
--
作者：
Zhao,JM;London,E
在高温下，白喉毒素的游离镍单体经历了中点为45-50℃的热变性状态的转变。在本报告中，将高温(60℃)构象与天然(中性pH)和低pH(pH<5)构象进行了比较。低pH和高温构象虽然不完全相同，但相似。与低pH构象中的蛋白质不同，与天然构象中的毒素不同，高温构象中的蛋白质具有疏水性，具有低荧光强度，并增加了色氨酸在水溶液中的暴露。在低pH条件下，高温下的圆二色谱最多只能显示部分二级结构的展开。相比之下，氯化胍中毒素的构象更接近于随机卷曲。高温和低pH的影响相互作用，使天然构象对一种构象的敏感性增加另一种。也就是说，天然状态和热变性状态之间的转变温度随着pH的降低而降低，中性-pH状态和低pH状态之间的转变pH随着温度的升高而增加。这意味着蛋白质上有一些区域，在那里高温和低pH可以以类似的方式破坏构象。综上所述，这些结果表明，低pH和高温构象都可以定义为部分变性状态，尽管在低pH下可能不会广泛展开。类似的行为也可能发生在其他蛋白质中，这些蛋白质在低pH值下发生功能上的重要构象破坏。
At high temperature, nicked free monomers of diphtheria toxin undergo a transition to a thermally denatured state, with a midpoint of 45-50 degrees C. In this report, the high-temperature (60 degrees C) conformation has been compared to the native (neutral pH) and low-pH (pH less than 5) conformations. The low-pH and high-temperature conformations are similar although not identical. As in the conformation at low pH, and unlike the toxin in its native conformation, the protein in its conformation at high temperature is hydrophobic, has low fluorescence intensity, and has increased exposure of tryptophan to aqueous solution. As at low pH, at high temperature the circular dichroism spectrum shows at most only partial unfolding of secondary structure. In contrast, the conformation of the toxin in guanidinium chloride is much closer to a random coil. The effects of high temperature and low pH interact in the sense that sensitivity of the native conformation to one is increased by the other. That is, the transition temperature between native and thermally denatured states is decreased as pH is decreased, and the transition pH between neutral-pH and low-pH states is increased as temperature is increased. This implies that there is some region on the protein where high temperature and low pH can disrupt conformation in a similar manner. Taken together, these results indicate that the low-pH and high-temperature conformations can both be defined as partially denatured states, even though unfolding may not be extensive at low pH. Similar behavior may occur in other proteins that undergo functionally important conformational disruption at low pH.