Transthyretin aggregation under partially denaturing conditions is a downhill polymerization
Transthyretin aggregation under partially denaturing conditions is a downhill polymerization
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DOI：
10.1021/bi049621l
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发表时间：
2004-06-15
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：
Hurshman, AR;White, JT;Kelly, JW
甲状腺素运载蛋白（TTR）在患者组织中的纤维和无定形聚集体的沉积是TTR淀粉样蛋白病的标志，但淀粉样蛋白生成的分子细节知之甚少。四聚体解离通常是TTR淀粉样纤维形成的限速因素，因此我们使用TTR的单体变体（M-TTR）来研究聚集机制。淀粉样蛋白形成通常被认为是成核依赖性过程，其中原纤维生长需要形成寡聚核，其是途径上能量最高的物质。根据该模型，原纤维形成的速率应通过添加预形成的聚集体或“种子”来加速，这有效地绕过成核步骤。在此，我们证明，M-TTR淀粉样蛋白在低pH值是一个复杂的，多步骤的反应，其动力学行为是不相容的成核依赖性聚合的预期。M-TTR聚集不加速接种，反应时程的依赖性是一阶的M-TTR浓度，符合二聚体核或无核的过程中，每个步骤是双分子和基本上不可逆的。这些研究表明，在部分变性条件下由M-TTR形成淀粉样蛋白是一种下坡聚合，其中最高能量的物质是天然单体。我们的研究结果强调了稳定TTR四聚体的治疗策略的重要性，并可能有助于解释为什么超过80种TTR变体与疾病相关。由M-TTR和其他淀粉样蛋白生成肽（如淀粉样蛋白β-肽和胰岛淀粉样蛋白多肽）形成淀粉样蛋白之间的差异表明，至少在迄今为止检查的条件下，这些多肽不具有共同的聚集机制。
The deposition of fibrils and amorphous aggregates of transthyretin (TTR) in patient tissues is a hallmark of TTR amyloid disease, but the molecular details of amyloidogenesis are poorly understood. Tetramer dissociation is typically rate-limiting for TTR amyloid fibril formation, so we have used a monomeric variant of TTR (M-TTR) to study the mechanism of aggregation. Amyloid formation is often considered to be a nucleation-dependent process, where fibril growth requires the formation of an oligomeric nucleus that is the highest energy species on the pathway. According to this model, the rate of fibril formation should be accelerated by the addition of preformed aggregates or "seeds", which effectively bypasses the nucleation step. Herein, we demonstrate that M-TTR amyloidogenesis at low pH is a complex, multistep reaction whose kinetic behavior is incompatible with the expectations for a nucleation-dependent polymerization. M-TTR aggregation is not accelerated by seeding, and the dependence of the reaction timecourse is first-order on the M-TTR concentration, consistent either with a dimeric nucleus or with a nonnucleated process where each step is bimolecular and essentially irreversible. These studies suggest that amyloid formation by M-TTR under partially denaturing conditions is a downhill polymerization, in which the highest energy species is the native monomer. Our results emphasize the importance of therapeutic strategies that stabilize the TTR tetramer and may help to explain why more than eighty TTR variants are disease-associated. The differences between amyloid formation by M-TTR and other amyloidogenic peptides (such as amyloid beta-peptide and islet amyloid polypeptide) demonstrate that these polypeptides do not share a common aggregation mechanism, at least under the conditions examined thus far.