Molecular mechanism of GTP binding- and dimerization-induced enhancement of Sar1-mediated membrane remodeling.
Molecular mechanism of GTP binding- and dimerization-induced enhancement of Sar1-mediated membrane remodeling.
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DOI：
10.1073/pnas.2212513120
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发表时间：
2023-02-21
影响因子：
11.1
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中科院分区：
文献类型：
--
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细胞机械如何驱动膜囊泡从细胞的一个区域到其他区域的出芽和运输仍有待更好地理解。这种出芽过程的基本机制是由具有特定结构基序的蛋白质（如两亲性螺旋）诱导膜弯曲。使用结合到不同核苷酸（GDP与GTP）和其GTP结合的二聚体形式的Sar 1蛋白作为例子，我们表明，虽然精确的氨基酸序列和插入深度的两亲性螺旋是相关的，所产生的膜曲率是最相关的蛋白质插入到膜的体积。因此，我们确定了一个潜在的分子机制，细胞如何可以激活涂层形成连接化学膜力学。通过在内质网上的亚结构域产生膜曲率，Sar 1 GTdR启动外壳蛋白II（COPII）介导的蛋白质转运，在内质网上它被鸟嘌呤核苷酸交换因子（GEF）Sec 12激活。GDP和GTP结合形式的SAR 1的晶体结构表明，它经历了一个构象开关，其中GTP结合增强了有效的膜渗透所必需的氨基末端两亲性螺旋的暴露。然而，在氨基末端的关键残基在晶体结构中没有解决，实验研究表明，在没有膜的情况下，即使在GDP结合状态下，Sar 1的氨基末端也是溶剂暴露的。因此，GTP结合激活Sar 1的膜重塑活性的分子机制仍不清楚。使用原子分子动力学模拟，我们比较了SAR 1在其GDP和GTP结合状态下的膜结合和曲率生成活动。我们发现，在GTP结合状态下，Sar 1插入到膜与其完整的（残基1至23）两亲性氨基末端螺旋，而Sar 1-GDP结合到膜仅通过其前12个残基。这种差异性膜结合模式转化为插入膜中的蛋白质体积的显著差异。因此，Sar 1-GTP产生的正膜曲率比Sar 1-GDP高10至20倍。Sar 1的GTP结合形式的二聚化进一步放大了曲率的产生。综上所述，我们的研究结果提出了一个详细的分子机制，如何核苷酸结合状态的Sar 1调节其膜结合和重塑活动的浓度依赖性的方式，铺平了道路，更好地了解COPII介导的膜转运。
How cellular machinery drives the budding and transport of membrane vesicles from one region of the cell to others remains to be better understood. The fundamental mechanism underlying this budding process is the induction of membrane curvature by proteins with specific structural motifs such as amphipathic helices. Using the Sar1 protein bound to different nucleotides (GDP vs. GTP) and its GTP-bound dimeric form as examples, we show that while the precise amino acid sequence and insertion depth of the amphipathic helix are relevant, the generated membrane curvature is most correlated with the volume of protein insertion into the membrane. Thus, we identify a potential molecular mechanism for how the cell can activate coat formation by connecting chemistry to membrane mechanics. The Sar1 GTPase initiates coat protein II (COPII)-mediated protein transport by generating membrane curvature at subdomains on the endoplasmic reticulum, where it is activated by the guanine nucleotide exchange factor (GEF) Sec12. Crystal structures of GDP- and GTP-bound forms of Sar1 suggest that it undergoes a conformational switch in which GTP binding enhances the exposure of an amino-terminal amphipathic helix necessary for efficient membrane penetration. However, key residues in the amino terminus were not resolved in crystal structures, and experimental studies have suggested that the amino terminus of Sar1 is solvent-exposed in the absence of a membrane, even in the GDP-bound state. Therefore, the molecular mechanism by which GTP binding activates the membrane-remodeling activity of Sar1 remains unclear. Using atomistic molecular dynamics simulations, we compare the membrane-binding and curvature generation activities of Sar1 in its GDP- and GTP-bound states. We show that in the GTP-bound state, Sar1 inserts into the membrane with its complete (residues 1 to 23) amphipathic amino-terminal helix, while Sar1-GDP binds to the membrane only through its first 12 residues. Such differential membrane-binding modes translate into significant differences in the protein volume inserted into the membrane. As a result, Sar1-GTP generates positive membrane curvature 10 to 20 times higher than Sar1-GDP. Dimerization of the GTP-bound form of Sar1 further amplifies curvature generation. Taken together, our results present a detailed molecular mechanism for how the nucleotide-bound state of Sar1 regulates its membrane-binding and remodeling activities in a concentration-dependent manner, paving the way toward a better understanding COPII-mediated membrane transport.
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影响因子：
16.6
作者：
Hutchings J;Stancheva V;Miller EA;Zanetti G
通讯作者：
Zanetti G
影响因子：
2.9
作者：
Antonny, B;BeraudDufour, S;Chabre, M
通讯作者：
Chabre, M
DOI：
10.1083/jcb.200509095
发表时间：
2005-12-19
期刊：
The Journal of cell biology
影响因子：
--
作者：
Bielli A;Haney CJ;Gabreski G;Watkins SC;Bannykh SI;Aridor M
通讯作者：
Aridor M
DOI：
10.1038/nrm3117
发表时间：
2011-06
期刊：
Nature reviews. Molecular cell biology
影响因子：
--
作者：
通讯作者：
--
影响因子：
5.6
作者：
Hariri, Hanaa;Bhattacharya, Nilakshee;Johnson, Kerri;Noble, Alex J.;Stagg, Scott M.
通讯作者：
Stagg, Scott M.