Structural Insight into pH-induced Conformational Changes within the Native Human Transthyretin Tetramer
Structural Insight into pH-induced Conformational Changes within the Native Human Transthyretin Tetramer
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DOI：
10.1016/j.jmb.2008.07.029
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发表时间：
2008-10-24
影响因子：
5.6
通讯作者：
Sacchettini, James C.
中科院分区：
文献类型：
--
作者：
Palaninathan, Satheesh K.;Mohamedmohaideen, Nilofar N.;Sacchettini, James C.
转甲状腺素四聚体的酸化促进了蛋白质的解离和构象变化，允许交替折叠的单体在体外通过下坡聚合机制自组装成不溶的淀粉样纤维。研究酸化对TTR四级和三级结构的影响，以及在pH条件下野生型人TTR四级和三级结构。PH值为3.5，分辨率为1.7埃。酸性H晶体与以前报道的大多数TTR结构相似，在不对称单元中包含两个亚基(所谓的A和B亚基)，但通过晶体对称性形成四聚体。PH为4.0的晶体结构表明，四聚体的天然折叠大部分保持不受干扰。特别是，TTRpH 4.0结构的A亚基与野生型TTRpH 7.4结构非常相似，具有r.m.s.d。0.38埃。相反，TTRpH 4.0结构的B亚基表现出几个显著的变化。EF-螺旋(残基75-81)和邻近的EF-环(残基82-90)显示r.m.s.d。大于2.0埃。该区域内的酸性残基(Glu72、Asp74、Glu89和Glu92)经历了显著的构象变化，引起EF螺旋环区的移动，并使Lys70、Lys76、His88和His90残基的侧链朝向这些酸性残基。特别是，Glu89经历了5.6埃的最大偏差，占据了Phe87‘S在野生型TTRpH 7.4结构中的初始位置，并将其侧链指向邻近亚基的疏水口袋。在pH 3.5的结构中，EF螺旋环区完全无序。这些结果表明，酸性条件增加了TTRB亚单位的EF螺旋环区经历构象变化和展开的敏感性，可能破坏四聚体的稳定，并至少识别出导致淀粉样变单体的四聚体内可能发生的初始构象变化。(C)2008年，爱思唯尔有限公司出版。
Acidification of the transthyretin (TTR) tetramer facilitates dissociation and conformational changes in the protein, allowing alternatively folded monomers to self-assemble into insoluble amyloid fibers by a downhill polymerization mechanism in vitro. To investigate the influence of acidification on the quaternary and tertiary structures of TTR, crystal structures of wild-type human TTR at pH. 4.0 and pH 3.5 have been determined to 1.7 angstrom resolution. The acidic H crystals are isomorphous to most of the previously reported TTR structures, containing two subunits in the asymmetric unit (the so-called A and B subunits) but forming a tetramer through crystallographic symmetry. The pH 4.0 crystal structure reveals that the native fold of the tetramer remains mostly undisturbed. In particular, subunit A of the TTR pH 4.0 structure is very similar to the wild-type TTR pH 7.4 structure with an r.m.s.d. of 0.38 angstrom. In contrast, subunit B of the TTR pH 4.0 structure exhibits several significant changes. The EF-helix (residues 75-81) and the adjacent EF-loop (residues 82-90) show an r.m.s.d. greater than 2.0 angstrom. The acidic residues within this region (Glu72, Asp74, Glu89, and Glu92) undergo significant conformational changes that instigate movement of the EF helix-loop region and make residues Lys70, Lys76, His88, and His90 orient their side chains toward these acidic residues. In particular, Glu89 undergoes a maximum deviation of 5.6 angstrom, occupying Phe87's initial position in the wildtype TTR pH 7.4 structure, and points its side chain into a hydrophobic pocket of the neighboring subunit. In the pH 3.5 structure, the EF helix-loop region is completely disordered. These results demonstrate that acidic conditions increase the susceptibility of the EF helix-loop region of the TTR B subunit to undergo conformational changes and unfold, likely destabilizing the tetramer and identifying at least the initial conformational changes likely occurring within the tetramer that leads to the amyloidogenic monomer. (C) 2008 Published by Elsevier Ltd.