High-Resolution X-Ray Structure of the Trimeric Scar/WAVE-Complex Precursor Brk1
High-Resolution X-Ray Structure of the Trimeric Scar/WAVE-Complex Precursor Brk1
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DOI：
10.1371/journal.pone.0021327
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发表时间：
2011-06-20
期刊：
影响因子：
3.7
通讯作者：
Faix, Jan
中科院分区：
文献类型：
--
作者：
Linkner, Joern;Witte, Gregor;Faix, Jan
Scar/ wave复合物将上游Rho-GTPase信号传导与保守的arp2 /3复合物的激活联系起来。Scar/ wave诱导和arp2 /3复合物介导的肌动蛋白成核对于肌动蛋白在凸出的板足中组装以驱动细胞迁移至关重要。异五聚体Scar/WAVE复合物由Scar/WAVE、Abi、Nap、Pir和一个小多肽Brk1/HSPC300组成，最近的研究表明，游离Brk1在该复合物的组装中充当了一个同聚前体。本研究通过超离心和凝胶过滤对Dictyostelium中的Brk1三聚体进行了表征。我们首次展示了其在纳摩尔浓度范围内的解离，以及不同DdBrk1含复合物内亚基的交换。此外，我们用x射线晶体学在1.5埃分辨率下确定了DdBrk1的三维结构。DdBrk1的三条链相互关联，形成平行的三线圈束。值得注意的是，这种结构与人类Scar/ wave复合物中HSPC300/WAVE1/Abi2的异三聚体α -螺旋束高度相似。这一发现，再加上Brk1被其他亚基夹在一起，也构成了连接HSPC300/WAVE1/Abi2/异源三聚体的三线圈结构域与Sra1（Pir1）的主要亚基，意味着该亚基在整个Scar/ wave复合物的组装过程中具有关键功能。
The Scar/WAVE-complex links upstream Rho-GTPase signaling to the activation of the conserved Arp2/3-complex. Scar/WAVE-induced and Arp2/3-complex-mediated actin nucleation is crucial for actin assembly in protruding lamellipodia to drive cell migration. The heteropentameric Scar/WAVE-complex is composed of Scar/WAVE, Abi, Nap, Pir and a small polypeptide Brk1/HSPC300, and recent work suggested that free Brk1 serves as a homooligomeric precursor in the assembly of this complex. Here we characterized the Brk1 trimer from Dictyostelium by analytical ultracentrifugation and gelfiltration. We show for the first time its dissociation at concentrations in the nanomolar range as well as an exchange of subunits within different DdBrk1 containing complexes. Moreover, we determined the three-dimensional structure of DdBrk1 at 1.5 angstrom resolution by X-ray crystallography. Three chains of DdBrk1 are associated with each other forming a parallel triple coiled-coil bundle. Notably, this structure is highly similar to the heterotrimeric alpha-helical bundle of HSPC300/WAVE1/Abi2 within the human Scar/WAVE-complex. This finding, together with the fact that Brk1 is collectively sandwiched by the remaining subunits and also constitutes the main subunit connecting the triple-coil domain of the HSPC300/WAVE1/Abi2/heterotrimer to Sra1( Pir1), implies a critical function of this subunit in the assembly process of the entire Scar/WAVE-complex.