Structural analysis of the complement control protein (CCP) modules of GABAB receptor 1a -: Only one of the two CCP modules is compactly folded
Structural analysis of the complement control protein (CCP) modules of GABAB receptor 1a -: Only one of the two CCP modules is compactly folded
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DOI：
10.1074/jbc.m406540200
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发表时间：
2004-11-12
影响因子：
4.8
通讯作者：
Barlow, PN
中科院分区：
文献类型：
--
作者：
Blein, S;Ginham, R;Barlow, PN
γ-氨基丁酸B型（GABA（B））受体是异二聚体G蛋白偶联受体。在人类中，GABA（B）受体1（R1）亚基的三种剪接变体的不同之处在于，在GABA结合结构域之前，在细胞外N端具有两个推定的补体控制蛋白（CCP）模块中的一个、两个或两个都不具有。这些预测模块的体内功能仍有待发现，但可能与细胞外基质蛋白的关联是有趣的。GABA（B）R1 a变体的包含其两个CCP模块样序列的部分已被表达，对应于每个单独模块的序列也已被表达。每个推定的CCP模块表现出预期的二硫键形成模式。然而，第二个模块（CCP 2）比第一个模块更复杂折叠，并且基于NMR衍生的核Overhauser效应解决了这个更C-末端模块（单独表达）的三维结构。这揭示了与先前确定的补体激活调节因子中的CCP模块结构的强烈相似性。无论是单独表达还是与CCP 2一起表达，N-末端模块（CCP 1）在广泛的条件下显示构象异质性。尽管事实上重组CCP 1有助于与细胞外基质蛋白fibulin-2结合，但几条证据表明CCP 1中存在天然病症。因此，我们已经表明，GABA（B）R1 a的两个CCP模块具有显著不同的结构特性，反映了它们不同的功能。
The gamma-aminobutyric acid type B (GABA(B)) receptor is a heterodimeric G-protein-coupled receptor. In humans, three splice variants of the GABA(B) receptor 1 (R1) subunit differ in having one, both, or neither of two putative complement control protein (CCP) modules at the extracellular N terminus, prior to the GABA-binding domain. The in vivo function of these predicted modules remains to be discovered, but a likely association with extracellular matrix proteins is intriguing. The portion of the GABA(B) R1a variant encompassing both of its CCP module-like sequences has been expressed, as have the sequences corresponding to each individual module. Each putative CCP module exhibits the expected pattern of disulfide formation. However, the second module (CCP2) is more compactly folded than the first, and the three-dimensional structure of this more C-terminal module (expressed alone) was solved on the basis of NMR-derived nuclear Overhauser effects. This revealed a strong similarity to previously determined CCP module structures in the regulators of complement activation. The N-terminal module (CCP1) displayed conformational heterogeneity under a wide range of conditions whether expressed alone or together with CCP2. Several lines of evidence indicated the presence of native disorder in CCP1, despite the fact that recombinant CCP1 contributes to binding to the extracellular matrix protein fibulin-2. Thus, we have shown that the two CCP modules of GABA(B) R1a have strikingly different structural properties, reflecting their different functions.