Fantini Jacques, Carlus Denis, Yahi Nouara
Universite Paul Cezanne, France.
Biochim Biophys Acta. 2011 Oct;1808(10):2343-51. doi: 10.1016/j.bbamem.2011.06.017. Epub 2011 Jul 5.
Parkinson's disease-associated α-synuclein is an amyloidogenic protein not only expressed in the cytoplasm of neurons, but also secreted in the extracellular space and internalized into glial cells through a lipid raft-dependent process. We previously showed that α-synuclein interacts with raft glycosphingolipids through a structural motif common to various viral and amyloidogenic proteins. Here we report that α-synuclein also interacts with cholesterol, as assessed by surface pressure measurements of cholesterol-containing monolayers. Using a panel of recombinant fragments and synthetic peptides, we identified two distinct cholesterol-binding domains in α-synuclein. One of these domains, which corresponds to the tilted peptide of α-synuclein (67-78), bound cholesterol with high affinity and was toxic for cultured astrocytes. Molecular modeling suggested that cholesterol binds to this peptide with a tilt angle of 46°. α-synuclein also contains a cholesterol recognition consensus motif, which had a lower affinity for cholesterol and was devoid of toxicity. This motif is encased in the glycosphingolipid-binding domain (34-45) of α-synuclein. In raft-like model membranes containing both cholesterol and glycosphingolipids, the head groups of glycosphingolipids prevented the accessibility of cholesterol to exogenous ligands. Nevertheless, cholesterol appeared to 'signal' its presence by tuning glycosphingolipid conformation, thereby facilitating α-synuclein binding to raft-like membranes. We propose that the association of α-synuclein with lipid rafts involves both the binding of α-synuclein (34-45) to glycosphingolipids, and the interaction of the fusogenic tilted peptide (67-78) with cholesterol. Coincidentally, a similar mechanism is used by viruses (HIV-1, HTLV-I, Ebola) which display a tilted peptide and fuse with host cell membranes through a sphingolipid/cholesterol-dependent process.
帕金森病相关的α-突触核蛋白是一种淀粉样蛋白，不仅在神经元细胞质中表达，还分泌到细胞外空间，并通过脂筏依赖性过程内化到神经胶质细胞中。我们之前表明，α-突触核蛋白通过各种病毒和淀粉样蛋白共有的结构基序与脂筏糖鞘脂相互作用。在此我们报告，通过含胆固醇单层的表面压力测量评估，α-突触核蛋白也与胆固醇相互作用。使用一组重组片段和合成肽，我们在α-突触核蛋白中鉴定出两个不同的胆固醇结合结构域。其中一个结构域对应于α-突触核蛋白的倾斜肽段（67 - 78），它以高亲和力结合胆固醇，并且对培养的星形胶质细胞有毒性。分子模拟表明胆固醇以46°的倾斜角结合到该肽段上。α-突触核蛋白还包含一个胆固醇识别共有基序，它对胆固醇的亲和力较低且无毒性。该基序包含在α-突触核蛋白的糖鞘脂结合结构域（34 - 45）中。在同时含有胆固醇和糖鞘脂的类脂筏模型膜中，糖鞘脂的头部基团阻止了胆固醇对外源配体的可及性。然而，胆固醇似乎通过调节糖鞘脂构象来“信号”其存在，从而促进α-突触核蛋白与类脂筏膜的结合。我们提出α-突触核蛋白与脂筏的结合涉及α-突触核蛋白（34 - 45）与糖鞘脂的结合，以及融合性倾斜肽段（67 - 78）与胆固醇的相互作用。巧合的是，病毒（HIV - 1、HTLV - I、埃博拉病毒）也使用类似机制，它们展示一个倾斜肽段并通过鞘脂/胆固醇依赖性过程与宿主细胞膜融合。
