Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06511, USA.
J Am Chem Soc. 2011 May 11;133(18):7152-8. doi: 10.1021/ja2009554. Epub 2011 Apr 14.
Both oxidative stress and aggregation of the protein α-synuclein (aS) have been implicated as key factors in the etiology of Parkinson's disease. Specifically, oxidative modifications to aS disrupt its binding to lipid membranes, an interaction considered critical to its native function. Here we seek to provide a mechanistic explanation for this phenomenon by investigating the effects of oxidative nitration of tyrosine residues on the structure of aS and its interaction with lipid membranes. Membrane binding is mediated by the first ∼95 residues of aS. We find that nitration of the single tyrosine (Y39) in this domain disrupts binding due to electrostatic repulsion. Moreover, we observe that nitration of the three tyrosines (Y125/133/136) in the C-terminal domain is equally effective in perturbing binding, an intriguing result given that the C-terminus is not thought to interact directly with the lipid bilayer. Our investigations show that tyrosine nitration results in a change of the conformational states populated by aS in solution, with the most prominent changes occurring in the C-terminal region. These results lead us to suggest that nitration of Y125/133/136 reduces the membrane-binding affinity of aS through allosteric coupling by altering the ensemble of conformational states and depopulating those capable of membrane binding. While allostery is a well-established concept for structured proteins, it has only recently been discussed in the context of disordered proteins. We propose that allosteric regulation through modification of specific residues in, or ligand binding to, the C-terminus may even be a general mechanism for modulating aS function.
氧化应激和蛋白质α-突触核蛋白（aS）的聚集都被认为是帕金森病发病机制的关键因素。具体来说，aS 的氧化修饰会破坏其与脂质膜的结合，这种相互作用被认为对其天然功能至关重要。在这里，我们通过研究酪氨酸残基氧化硝化对 aS 结构及其与脂质膜相互作用的影响，试图为此现象提供一种机制解释。膜结合是由 aS 的前约 95 个残基介导的。我们发现，该结构域中单一酪氨酸（Y39）的硝化会由于静电排斥而破坏结合。此外，我们观察到 C 末端的三个酪氨酸（Y125/133/136）的硝化同样有效地干扰结合，这是一个有趣的结果，因为 C 末端不被认为直接与脂质双层相互作用。我们的研究表明，酪氨酸硝化导致 aS 在溶液中占据的构象状态发生变化，C 末端区域的变化最为明显。这些结果使我们推测，Y125/133/136 的硝化通过改变构象状态的整体分布并使那些能够与膜结合的构象状态失活，从而降低 aS 的膜结合亲和力。虽然变构作用是构象蛋白的一个成熟概念，但它最近才在无序蛋白的背景下被讨论。我们提出，通过修饰 C 末端的特定残基或配体与 C 末端的结合来进行变构调节，甚至可能是调节 aS 功能的一般机制。
