Evolutionary and functional divergence between the cystic fibrosis transmembrane conductance regulator and related ATP-binding cassette transporters
Evolutionary and functional divergence between the cystic fibrosis transmembrane conductance regulator and related ATP-binding cassette transporters
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DOI：
10.1073/pnas.0806306105
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发表时间：
2008-12-02
影响因子：
11.1
通讯作者：
McCarty, Nael A.
中科院分区：
文献类型：
--
作者：
Jordan, I. King;Kota, Karthik C.;McCarty, Nael A.
囊性纤维化跨膜电导调节因子 (CFTR) 是 ATP 结合盒 (ABC) 转运蛋白超家族的成员，该超家族是一个古老的蛋白质家族，存在于所有门中。几乎在所有情况下，ABC 蛋白都是转运蛋白，通过交替访问机制将 ATP 的水解与底物的跨膜运动耦合起来。相比之下，CFTR 因其作为 ATP 依赖性氯离子通道的活性而闻名。我们想知道为什么 CFTR 与 ABC 蛋白具有转运蛋白的结构域结构，却表现出功能上的差异。我们将CFTR蛋白序列与其他ABC转运蛋白序列进行比较，确定ABCC4蛋白是最接近的哺乳动物旁系同源物，并使用CFTR-ABCC4多重序列比对的统计分析来鉴定最有可能参与从转运蛋白到通道活性的进化转变的特定结构域和残基。由于既具有 CFTR 特异性又在所有 CFTR 直向同源物中保守，被鉴定为参与 CFTR 功能分歧的残基中，第 8352 个残基位于第六跨膜螺旋 (TM6) 中。膜片钳实验表明8352与TM9中的D993相互作用以稳定开放通道状态； D993 在 CFTR 和 ABCC4 之间绝对保守。这些数据表明，CFTR 通道活性至少部分是通过将与 ATP 结合和水解相关的构象变化（如在真正的 ABC 转运蛋白中发现的）通过稳定开放状态的蛋白内相互作用转化为开放渗透途径而进化的。该分析为理解 CFTR 成为独特的 ABC 转运蛋白的进化和功能关系奠定了基础。
The cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ATP-binding cassette (ABC) transporter superfamily, an ancient family of proteins found in all phyla. In nearly all cases, ABC proteins are transporters that couple the hydrolysis of ATP to the transmembrane movement of substrate via an alternating access mechanism. In contrast, CFTR is best known for its activity as an ATP-dependent chloride channel. We asked why CFTR, which shares the domain architecture of ABC proteins that function as transporters, exhibits functional divergence. We compared CFTR protein sequences to those of other ABC transporters, which identified the ABCC4 proteins as the closest mammalian paralogs, and used statistical analysis of the CFTR-ABCC4 multiple sequence alignment to identify the specific domains and residues most likely to be involved in the evolutionary transition from transporter to channel activity. Among the residues identified as being involved in CFTR functional divergence, by virtue of being both CFTR-specific and conserved among all CFTR orthologs, was 8352 in the sixth transmembrane helix (TM6). Patch-clamp experiments show that 8352 interacts with D993 in TM9 to stabilize the open-channel state; D993 is absolutely conserved between CFTRs and ABCC4s. These data suggest that CFTR channel activity evolved, at least in part, by converting the conformational changes associated with binding and hydrolysis of ATP, as are found in true ABC Transporters, into an open permeation pathway by means of intraprotein interactions that stabilize the open state. This analysis sets the stage for understanding the evolutionary and functional relationships that make CFTR a unique ABC transporter protein.