Parallel homodimer structures of the extracellular domains of the voltage-gated sodium channel β4 subunit explain its role in cell-cell adhesion.
Parallel homodimer structures of the extracellular domains of the voltage-gated sodium channel β4 subunit explain its role in cell-cell adhesion.
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DOI：
10.1074/jbc.m117.786509
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发表时间：
2017-08-11
期刊：
影响因子：
--
通讯作者：
Yokoyama S
中科院分区：
文献类型：
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作者：
Shimizu H;Tosaki A;Ohsawa N;Ishizuka-Katsura Y;Shoji S;Miyazaki H;Oyama F;Terada T;Shirouzu M;Sekine SI;Nukina N;Yokoyama S
电压门控钠通道 (VGSC) 是可兴奋细胞中产生动作电位所需的跨膜蛋白，对于沿神经细胞传播电脉冲至关重要。 VGSC 是成孔 α 亚基和辅助 β 亚基的复合物，称为 β1/β1B-β4（分别由 SCN1B-4B 编码），也在细胞间粘附中发挥作用。我们之前报道了β4亚基反式同亲相互作用的结构基础，这有助于其粘附功能。在这里，使用晶体学和生化分析，我们表明β4胞外结构域以平行方式直接相互作用，涉及连接B链和C链的环中不成对的Cys残基（Cys58）之间的分子间二硫键以及N端片段（Ser30-Val35）的分子间疏水和氢键相互作用。在还原条件下，与野生型相比，N末端缺失的β4突变体表现出细胞粘附力降低，表明β4顺式二聚体有助于细胞间粘附中β4的反式同亲相互作用。此外，该突变体表现出与α亚基的关联增加，表明β4的顺式二聚化影响α-β4复合物的形成。这些观察结果为 VGSC 中 β4 平行二聚体的形成提供了结构基础，并揭示了其细胞间粘附的机制。
Voltage-gated sodium channels (VGSCs) are transmembrane proteins required for the generation of action potentials in excitable cells and essential for propagating electrical impulses along nerve cells. VGSCs are complexes of a pore-forming α subunit and auxiliary β subunits, designated as β1/β1B–β4 (encoded by SCN1B–4B, respectively), which also function in cell–cell adhesion. We previously reported the structural basis for the trans homophilic interaction of the β4 subunit, which contributes to its adhesive function. Here, using crystallographic and biochemical analyses, we show that the β4 extracellular domains directly interact with each other in a parallel manner that involves an intermolecular disulfide bond between the unpaired Cys residues (Cys58) in the loop connecting strands B and C and intermolecular hydrophobic and hydrogen-bonding interactions of the N-terminal segments (Ser30-Val35). Under reducing conditions, an N-terminally deleted β4 mutant exhibited decreased cell adhesion compared with the wild type, indicating that the β4 cis dimer contributes to the trans homophilic interaction of β4 in cell–cell adhesion. Furthermore, this mutant exhibited increased association with the α subunit, indicating that the cis dimerization of β4 affects α–β4 complex formation. These observations provide the structural basis for the parallel dimer formation of β4 in VGSCs and reveal its mechanism in cell–cell adhesion.