Structure and membrane binding of alpha-synuclein

α-突触核蛋白(AS)是一种小的突触前蛋白，与帕金森病的发病机制有关。它在本质上无序的胞浆状态和更有结构的囊泡结合状态之间进行划分。过去对AS的结构研究主要基于SDS洗涤剂结合的条件，在该条件下，AS在N-末端结构域上显示两个α-螺旋，在溶液中保持自由的非结构化C-末端尾巴。我们研究了在模拟突触前囊泡膜成分的磷脂小泡存在的情况下，AS的结构和生物物理学。核磁共振检测到对磷脂有很高的亲和力，得到亲和力Kd为50um，这强烈地表明在细胞环境中，蛋白质将处于膜结合状态的99.9%。转移NOE实验表明，蛋白质在膜结合状态下是高度螺旋的，与先前的实验数据相反，C-末端40个残基也参与了与膜的直接相互作用。可以区分出四种不同的与膜的结合模式，其相对数量取决于AS：脂质摩尔比。这些结合模式中的一种与加速纤维形成有关。

Alpha-synuclein (aS) is a small presynaptic protein implicated in the pathogenesis of Parkinsons disease. It partitions between an intrinsically disordered cytosolic state and a more structured vesicle-bound state. Past structural studies of aS have been based largely on the SDS detergent-bound conditions, for which aS displays two alpha-helices in the N-terminal domain and an unstructured C-terminal tail that remains free in solution. We have investigated the structure and biophysics of aS in the presence of phospholipid vesicles that mimic the membrane composition of presynaptic vesicles. Very high affinity for phospholipids is measured by NMR, yielding an affinity Kd of 50 uM, which strongly suggests that in the cellular environment the protein will be >99.9% in the membrane bound state. Transferred NOE experiments indicate that the protein is highly helical in the membrane bound state, and that in contrast to prior experimental data, the C-terminal 40 residues also participate in direct interactions with the membrane. Four distinct binding modes with the membrane can be distinguished, whose relative populations depend on the aS:lipid molar ratio. One of these binding modes is implicated in accelerated fibril formation.