Theoretical study of structure-function correlations of Aquaporin V and mutants

描述(申请人提供)：13种人类水通道蛋白(AQP0-AQP12)分布在胃、十二指肠、胰腺、呼吸道、肺、唾液腺、汗腺、眼睛、泪腺和内耳的细胞中，其中AQP5与干燥症以及肺癌、胰腺癌、结肠癌等有关。AQP5的缺陷交易被发现是干燥病的罪魁祸首，该病在美国造成约400万人(主要是女性)的死亡。AQP5过表达可促进细胞增殖，抑制细胞凋亡。同时，最近还确定了AQP5的高分辨X射线结构。AQP5在其四聚体构象和由每个原基形成的水孔结构上与其他水通道蛋白相似。然而，它缺乏四个原型之间的四重准对称性，并且它的中央毛孔中含有一种脂类PS6。鉴于目前对水通道蛋白5的S功能及其晶体结构的研究，突出的问题是：生理条件下包埋在细胞膜上的水通道蛋白5的结构是如何偏离其晶体形态的？PS6是关闭还是抑制中央毛孔？脂质-AQP5相互作用的特异性是什么？这种蛋白质如何对其在pH中的环境变化做出反应？它对其残留物的化学修饰有何反应？在设计专门针对AQP5的新药之前，需要回答这些关于AQP5结构与功能相关性的问题。回答这些问题需要以一种创新的方法进行广泛的电子实验。AQP5的两个全原子模型系统将被研究：一个在AQP5的中心孔中有PS6，另一个没有。我们将追求三个具体目标：1.确定脂质在中央毛孔中的作用，并确定其关闭或抑制作用的机制。2.确定蛋白质的生物学功能机制，并确定其对环境变化的反应。3.量化AQP5‘S对化学修饰的反应，从而确定其信号、门控或抑制其生理功能的机制。研究完成后，将对AQP5的S结构与功能的相关性有一个详细的了解：AQP5的S在所选位点磷酸化前后的转运可及度，与其中央孔中的脂类结合的亲和力和特异性，以及抑制和抑制其生理功能的机制。所获得的知识将对寻找预防和控制AQP5相关疾病的新药产生积极影响。

DESCRIPTION (provided by applicant): Among the thirteen human aquaporins (AQP0-AQP12) distributed within cells of the stomach, duodenum, pancreas, airways, lungs, salivary glands, sweat glands, eyes, lacrimal glands, and the inner ear, AQP5 has been implicated in Sjogren's disease and in cancers of the lung, pancreas, colon etc.. Defective trafficking of AQP5 was found responsible for Sjogren's disease which inflicts about 4 million people (mostly women) in the US. Overexpression of AQP5 was identified in promoting cell proliferation and inhibiting apoptosis. Meanwhile, high-resolution x-ray structure of AQP5 has recently been determined. AQP5 resembles other aquaporins in its tetrameric conformation and in its water pore structure formed by each protomer. However, it lacks the four-fold quasi-symmetry among its four protomers and it contains a lipid, PS6, in its central pore. In light of the existent in vtro studies of AQP5's functions and its crystal structure, the following questions stand out: How does the structure of AQP5 embedded in the cell membrane under physiological conditions deviate from its crystallographic form? Does PS6 gate or inhibit the central pore? What are the specificities of the lipid-AQP5 interaction? How does the protein respond to its environmental changes in pH? And how does it respond to chemical modifications to its residues? These questions on the structure-function correlations of AQP5 need to be answered before new drugs can be designed that specifically target this protein. Answering these questions requires conducting extensive in silico experiments in an innovated approach. Two all-atom model systems of AQP5 embedded in a patch of lipid bi- layer explicitly solvated in physiological saline will be investigated: One with PS6 in the central pore of AQP5 and one without. Three specific aims will be pursued: 1.Determine the roles of the lipid in the central pore and identify the mechanism of its gating or inhibiting action. 2. Identify the protein's mechanisms of biological functions and determine its response to environmental changes. 3. Quantify AQP5's response to chemical modifications and thus identify the mechanisms of signaling, gating, or inhibiting its physiological functions. Upon completion of the proposed research, a detailed understanding will be achieved about AQP5's structure- function correlations: AQP5's degree of accessibility for trafficking before and after phosphorylation at the selected sites, the affinity and specificit of binding a lipid in its central pore, and the mechanisms of inhibiting and gating its physiological functions. The knowledge so gained will positively impact on finding new medicines to prevent and control AQP5-related diseases.