Molecular Pathophysiology of Cystic Fibrosis

描述(由申请人提供)：囊性纤维化(CF)是美国最常见的致命遗传病，由CFTR(囊性纤维化跨膜传导调节因子)基因功能丧失突变所致。作为ABC(三磷酸腺苷结合盒)转运体超家族的成员，CFTR含有两个核苷酸结合域(Nbd1和Nbd2)和一个签名序列(即LSGGQ)，其中Nbd1和Nbd2以典型的Walker A基序和B基序为特征，在ATP结合时形成头尾相连的NBD二聚体。CFTR的独特之处在于，它不是一种活跃的转运蛋白，而是一种真正的离子通道，它利用ATP来驱动其门控转换中的构象变化。我们过去的研究为CFTR的门控机制提供了新的见解。与普遍认为ATP水解严格耦合于门控循环的观点相反，这一观点得到了流行模型的支持，该模型描述了每个NBD/TMD复合体作为ABC转运体的刚体同步运动，而我们的数据支持一种挑衅性的替代方案，即这两个结构域独立而又能量耦合。[这一新机制被证明从机械上解释了FDA批准的治疗CF的药物VX-770(IVAAFTOR)是如何通过利用TMD和NBD之间这种明显不完美的耦合来发挥作用的。]我们最近对CFTR离子渗透途径的生物物理研究也为我们提出基本问题奠定了坚实的基础，例如(目标1)：孔隙是由什么组成的？中国铁路总公司的登机口在哪里？CFTR是如何选择阴离子与阳离子的？我们对疾病相关G551D突变中表现出的门控缺陷的机制研究不仅挑战了一家主要制药公司的数据，我们的结果还提出了一个有趣和可测试的假设，即签名序列中的这种甘氨酸到天冬氨酸的突变将催化能力强的ATP结合位点转化为抑制位点(目标2)。[我们相信，从分子细节上清楚地了解CFTR的功能，以及VX-770等药物如何影响CFTR功能的不同方面(目标3)，将有助于设计治疗CF、分泌性腹泻和其他CFTR相关疾病的治疗试剂。]

DESCRIPTION (provided by applicant): Cystic fibrosis (CF), the most common fatal genetic disease in the US, results from loss- of-function mutations in the CFTR (Cystic Fibrosis Transmembrane conductance Regulator) gene. As a member of the ABC (ATP Binding Cassette) transporter superfamily, CFTR harbors two nucleotide binding domains (NBD1 and NBD2) characterized by the canonical Walker A and B motifs for ATP binding/hydrolysis, and a signature sequence (i.e., LSGGQ) that plays a critical role for the formation of a head-to- tail NBD dimer upon ATP binding. CFTR is unique in that, instead of being an active transporter, CFTR is a bona fide ion channel, which utilizes ATP to drive conformational changes in its gating transitions. Our studies in the past have provided novel insights into the gating mechanism of CFTR. Contrary to the prevailing view that ATP hydrolysis is strictly coupled to the gating cycle, an idea supported by the popular model depicting that each NBD/TMD complex moves synchronously as a rigid body for ABC transporters, our data support a provocative alternative that these two domains assume autonomy on its own but are coupled energetically. [This novel mechanism turns out to explain mechanistically how an FDA-approved drug for CF treatment, VX-770 (Ivacaftor), works by exploiting this apparently imperfect coupling between TMDs and NBDs.] Our recent biophysical studies of CFTR's ion permeation pathway also establish a solid foundation for us to ask fundamental questions such as (Aim 1): What make up the pore? Where is the gate of CFTR? How does CFTR select anions versus cations? Our mechanistic studies of the gating defects manifested in the disease-associated G551D mutation not only challenge data from a major pharmaceutical company, our results also suggest an intriguing and testable hypothesis that this glycine-to-aspartate mutation in the signature sequence converts the catalysis-competent ATP binding site to an inhibitory site (Aim 2). [We believe a clear understanding of the CFTR function to a molecular detail and of how drugs such as VX-770 affect different aspects of CFTR function (Aim 3) will aid in the design of therapeutic reagents for the treatment of CF, secretory diarrhea, and other CFTR-associated diseases.]