Low-resolution solution structures of Munc18:Syntaxin protein complexes indicate an open binding mode driven by the Syntaxin N-peptide
Low-resolution solution structures of Munc18:Syntaxin protein complexes indicate an open binding mode driven by the Syntaxin N-peptide
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DOI：
10.1073/pnas.1116975109
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发表时间：
2012-06-19
影响因子：
11.1
通讯作者：
Martin, Jennifer L.
中科院分区：
文献类型：
--
作者：
Christie, Michelle P.;Whitten, Andrew E.;Martin, Jennifer L.
当神经细胞交流时，来自一个神经元的小泡与突触前膜融合，释放出化学物质，向下一个神经元发出信号。类似地，当胰岛素与脂肪细胞或肌肉上的受体结合时，葡萄糖转运蛋白-4囊泡与细胞膜融合，从而允许葡萄糖输入。这些基本过程需要囊泡和细胞膜上的SNARE蛋白相互作用，以及与SNARE蛋白Synaxin结合的神秘蛋白Munc18。在这里，我们证明了在溶液中，神经元蛋白Synaxin1a与Munc18-1相互作用，无论是否存在Synaxin1a N肽。相反，脂肪细胞蛋白Synaxin4不与其伴侣Munc18c结合，除非存在N-肽。Munc18-1：Synaxin1a复合体在没有N-肽的情况下的溶液散射数据表明，该复合体采用了抑制性闭合结合模式，这一点以该复合体的晶体结构为例。然而，当N-肽存在时，溶液散射数据表明Synaxin1a和Synaxin4都在与其各自的Munc18配对的络合物中采用扩展构象。利用交联质谱、小角X射线散射和小角中子散射随对比度变化的数据对开放Munc18：Synaxin结合模式的低分辨溶液结构进行了建模，表明与封闭结合模式相比，Munc18：Synaxin结合模式的相互作用有显著差异。总体而言，我们的结果表明，神经元Munc18-1：Synaxin1a蛋白可以采用两种交替的和功能不同的结合模式，关闭的和开放的，这取决于N-肽的存在，而Munc18c：Synaxin4只采用开放结合模式。
When nerve cells communicate, vesicles from one neuron fuse with the presynaptic membrane releasing chemicals that signal to the next. Similarly, when insulin binds its receptor on adipocytes or muscle, glucose transporter-4 vesicles fuse with the cell membrane, allowing glucose to be imported. These essential processes require the interaction of SNARE proteins on vesicle and cell membranes, as well as the enigmatic protein Munc18 that binds the SNARE protein Syntaxin. Here, we show that in solution the neuronal protein Syntaxin1a interacts with Munc18-1 whether or not the Syntaxin1a N-peptide is present. Conversely, the adipocyte protein Syntaxin4 does not bind its partner Munc18c unless the N-peptide is present. Solution-scattering data for the Munc18-1:Syntaxin1a complex in the absence of the N-peptide indicates that this complex adopts the inhibitory closed binding mode, exemplified by a crystal structure of the complex. However, when the N-peptide is present, the solution-scattering data indicate both Syntaxin1a and Syntaxin4 adopt extended conformations in complexes with their respective Munc18 partners. The low-resolution solution structure of the open Munc18:Syntaxin binding mode was modeled using data from cross-linking/mass spectrometry, small-angle X-ray scattering, and small-angle neutron scattering with contrast variation, indicating significant differences in Munc18:Syntaxin interactions compared with the closed binding mode. Overall, our results indicate that the neuronal Munc18-1:Syntaxin1a proteins can adopt two alternate and functionally distinct binding modes, closed and open, depending on the presence of the N-peptide, whereas Munc18c:Syntaxin4 adopts only the open binding mode.