Structural Requirements for VAP-B Oligomerization and Their Implication in Amyotrophic Lateral Sclerosis-associated VAP-B(P56S) Neurotoxicity
Structural Requirements for VAP-B Oligomerization and Their Implication in Amyotrophic Lateral Sclerosis-associated VAP-B(P56S) Neurotoxicity
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DOI：
10.1074/jbc.m109.097345
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发表时间：
2010-04-30
影响因子：
4.8
通讯作者：
Lev, Sima
中科院分区：
文献类型：
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作者：
Kim, SoHui;Leal, Sonia S.;Lev, Sima
整体内质网（ER）膜蛋白VAP-B通过其n端MSP结构域与含有FFAT基元的各种脂质转移/结合蛋白相互作用。在家族性运动神经元疾病中发现了其MSP结构域P56S的基因突变。这种突变通过一种未知的机制诱导不溶性VAP-B（P56S）蛋白聚集体的形成。在这项研究中，我们定义了VAP-B寡聚化的结构要求，并证明了它们对VAP-B（P56S）聚集和神经毒性的贡献。我们发现VAP-B的寡聚化主要是由其卷曲的线圈结构域介导的，跨膜结构域内的GXXXG二聚化基序介导跨膜结构域的自结合，但不足以驱动VAP-B的寡聚化。我们进一步证明了野生型VAP-B的寡聚化与它的MSP结构域无关。然而，我们发现P56S突变诱导MSP结构域内的构象变化，并通过将疏水斑块暴露于溶剂中促进其聚集倾向。这些构象变化对FFAT结合没有直接影响。相反，它们增强了由螺旋结构域和跨膜结构域共同驱动的VAP-B（P56S）寡聚化，从而阻止了对ffat结合位点的可及性，促进了VAP-B（P56S）不溶性聚集体的产生，从而导致其神经毒性。这些结果揭示了VAP-B（P56S）聚集体形成和诱导家族性运动神经元疾病的机制。
The integral endoplasmic reticulum (ER)-membrane protein VAP-B interacts with various lipid-transfer/binding proteins containing an FFAT motif through its N-terminal MSP domain. A genetic mutation within its MSP domain, P56S, was identified in familial forms of motor neuron diseases. This mutation induces the formation of insoluble VAP-B(P56S) protein aggregates by an unknown mechanism. In this study, we defined the structural requirements for VAP-B oligomerization and demonstrated their contribution for VAP-B(P56S) aggregation and neurotoxicity. We show that the oligomerization of VAP-B is mainly mediated by its coiled-coil domain and that the GXXXG dimerization motif within the transmembrane domain mediates transmembrane domains self-association but is insufficient to drive VAP-B oligomerization. We further show that the oligomerization of the wild-type VAP-B is independent of its MSP domain. However, we found that the P56S mutation induces conformational changes within the MSP domain and facilitates its propensity to aggregate by exposing hydrophobic patches to the solvent. These conformational changes have no direct effect on FFAT binding. Rather, they enhance VAP-B(P56S) oligomerization driven by the combined contributions of the coiled-coil and the transmembrane domains, thereby preventing accessibility to FFAT-binding site, facilitating the production of VAP-B(P56S)-insoluble aggregates and consequently its neurotoxicity. These results shed light on the mechanism by which VAP-B(P56S) aggregates are formed and induce familial motor neuron diseases.