Anion shielding of electrostatic repulsions in transthyretin modulates stability and amyloidosis:: Insight into the chaotrope unfolding dichotomy
Anion shielding of electrostatic repulsions in transthyretin modulates stability and amyloidosis:: Insight into the chaotrope unfolding dichotomy
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DOI：
10.1021/bi010673
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发表时间：
2001-09-25
期刊：
影响因子：
2.9
通讯作者：
Kelly, JW
中科院分区：
文献类型：
--
作者：
Hammarström, P;Jiang, X;Kelly, JW
稳定力和局部静电斥力之间的平衡可以通过阴离子屏蔽来调节甲状腺素（TTR）四聚体的不稳定性。TTR中两个对称的阴离子相互作用位点由两个甲状腺素结合位点周围相对亚基的Lys15和Lys15残基组成。它们是-铵基团的一个元素，相互排斥，使四聚体不稳定，除非有一个合适的阴离子存在，使四聚体稳定。TTR的乱向变性表现出不同寻常的行为，尿素似乎是比GdmCl（氯化胍）更强的变性剂，尽管GdmCl通常是变性剂的两倍。随着KCI浓度的增加，尿素变性曲线的中点向较高浓度的移动，以及高度耐变性的四聚体的摩尔分数的增加，有力地证明了阴离子屏蔽可以稳定TTR四聚体。四聚体稳定的结果是折叠滞后，因为阴离子稳定的四聚体变性所需的高GdmCl浓度不允许未折叠的单体重新折叠。TTR形成淀粉样蛋白原纤维需要其正常的四聚体结构解离成可选择折叠的单体，这一过程由酸化介导（pH 5-4）。这一过程被Cl-离子以浓度依赖性的方式抑制。氯离子可能不是相关的生理TTR稳定性调节剂，但它是这些研究的主要焦点，解释了GdmCl变性和重折叠研究中观察到的滞后现象。
The balance between stabilizing forces and the localized electrostatic repulsions destabilizing the transthyretin (TTR) tetramer is tunable via anion shielding. The two symmetrical anion interaction sites in TTR are comprised of residues Lys15 and Lys15 from opposing subunits on the periphery of the two thyroxine binding sites. These is an element of -ammonium groups repel one another and destabilize the tetramer, unless an appropriate anion is present, which stabilizes the tetramer. Chaotrope denaturation of TTR exhibits unusual behavior in that urea appears to be a stronger denaturant than GdmCl (guanidinium chloride), even though GdmCl is typically twice as powerful as a denaturant. The shift in the midpoint of the urea denaturation curve to higher concentrations as well as the increase in the mole fraction of tetramer that is highly resistant to denaturation with increasing KCI concentration provides strong evidence that anion shielding stabilizes the TTR tetramer. A consequence of tetramer stabilization is folding hysteresis, because the high GdmCl concentrations required to denature the anion-stabilized tetramer do not allow refolding of the unfolded monomers. The formation of amyloid fibrils by TTR requires that its normal tetrameric structure dissociate to alternatively folded monomers, a process mediated by acidification (pH 5-4). This process is inhibited by Cl- ions in a concentration-dependent fashion. Chloride ion may not be the relevant physiological TTR stability modulator, but it is the main focus of these studies explaining the hysteresis observed in the denaturation and refolding studies with GdmCl.