Computational and Systems Biology Initiative, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA.
J Am Chem Soc. 2013 Mar 13;135(10):3865-72. doi: 10.1021/ja310518p. Epub 2013 Feb 27.
α-Synuclein, a protein that forms ordered aggregates in the brains of patients with Parkinson's disease, is intrinsically disordered in the monomeric state. Several studies, however, suggest that it can form soluble multimers in vivo that have significant secondary structure content. A number of studies demonstrate that α-synuclein can form β-strand-rich oligomers that are neurotoxic, and recent observations argue for the existence of soluble helical tetrameric species in cellulo that do not form toxic aggregates. To gain further insight into the different types of multimeric states that this protein can adopt, we generated an ensemble for an α-synuclein construct that contains a 10-residue N-terminal extension, which forms multimers when isolated from Escherichia coli. Data from NMR chemical shifts and residual dipolar couplings were used to guide the construction of the ensemble. Our data suggest that the dominant state of this ensemble is a disordered monomer, complemented by a small fraction of helical trimers and tetramers. Interestingly, the ensemble also contains trimeric and tetrameric oligomers that are rich in β-strand content. These data help to reconcile seemingly contradictory observations that indicate the presence of a helical tetramer in cellulo on the one hand, and a disordered monomer on the other. Furthermore, our findings are consistent with the notion that the helical tetrameric state provides a mechanism for storing α-synuclein when the protein concentration is high, thereby preventing non-membrane-bound monomers from aggregating.
α-突触核蛋白是一种在帕金森病患者大脑中形成有序聚集物的蛋白质，在单体状态下是无规卷曲的。然而，有几项研究表明，它可以在体内形成具有显著二级结构含量的可溶性多聚体。许多研究表明，α-突触核蛋白可以形成富含β-折叠的寡聚体，这些寡聚体具有神经毒性，最近的观察结果也表明，在细胞内存在可溶性螺旋四聚体物种，这些物种不会形成有毒的聚集物。为了更深入地了解这种蛋白质可以采用的不同类型的多聚体状态，我们生成了一个包含 10 个残基 N 端延伸的α-突触核蛋白构建体的集合体，该构建体在从大肠杆菌中分离时会形成多聚体。来自 NMR 化学位移和残差偶极耦合的数据用于指导集合体的构建。我们的数据表明，该集合体的主要状态是无序单体，辅之以少量的螺旋三聚体和四聚体。有趣的是，该集合体还包含富含β-折叠的三聚体和四聚体寡聚体。这些数据有助于调和看似矛盾的观察结果，一方面表明细胞内存在螺旋四聚体，另一方面表明存在无序单体。此外，我们的发现与以下观点一致，即当蛋白质浓度较高时，螺旋四聚体状态为α-突触核蛋白的储存提供了一种机制，从而防止非膜结合单体聚集。
