The Biology of NBCe1 in Health and Disease

描述（由申请人提供）：膜转运蛋白SLC 4家族介导Cl--HCO 3-和Na+-驱动的Cl--HCO 3-交换，以及Na+-HCO 3-共转运（产电、电中性）。这些转运蛋白在哺乳动物细胞生物学中的重要性通过由人类中的自发SLC 4突变和小鼠中的靶向缺失引起的表型异常而突出。SLC 4家族某些成员的功能和/或质膜表达异常是人类多种遗传性疾病的原因，在已知的SLC 4基因中，SLC 4A 4（NBCe 1）和SLC 4A 1（AE 1）在介导肾脏碳酸氢盐吸收、维持全身和细胞内酸碱平衡中起关键作用。NBCe 1突变损害近端小管和肾外酸碱转运。在初步实验中，我们已经开始研究NBCe 1功能特性的结构基础，并取得了一些新的发现，这些发现构成了这一提议的背景。对NBCe 1的阴离子结合机制的初步研究发现，它同时具有产电Na+-CO 32-共转运体和电中性Na+-NO3-共转运体的功能。NBCe 1突变导致肾小管酸中毒也抑制NO3-转运。基于这些新发现，NBCe 1现在必须被认为是一种双功能转运蛋白，介导近端小管中的碳酸盐和硝酸盐转运，并可能在其表达的肾外组织中。鉴于我们的发现，NBCe 1运输Na+-CO 32-和Na+-NO3-，肾脏和近端小管在器官间NO3-循环和全身NO3-平衡中的作用从生理和临床的角度来看变得特别相关。该提案将表征NBCe 1作为产电Na+-CO 32-协同转运蛋白和电中性Na+-NO3-协同转运蛋白的功能的结构基础，这些功能特性在疾病中的扰动，以及NBCe 1和近端小管在NO3-转运中的作用。

DESCRIPTION (provided by applicant): The SLC4 family of membrane transporters mediate Cl--HCO3- and Na+-driven Cl--HCO3- exchange, and Na+- HCO3- cotransport (electrogenic, electroneutral). The importance of these transporters in mammalian cell biology is highlighted by the phenotypic abnormalities resulting from spontaneous SLC4 mutations in humans and targeted deletions in mice. Abnormalities in either the function and/or plasma membrane expression of certain members of the SLC4 family are the cause of various genetic diseases in man. Of the known SLC4 genes, SLC4A4 (NBCe1) and SLC4A1 (AE1) play key roles in mediating renal bicarbonate absorption, and the maintenance of systemic and intracellular acid-base balance. Mutations in NBCe1 impair both proximal tubule and extrarenal acid-base transport. In preliminary experiments, we have begun to examine the structural basis for the functional properties of NBCe1 and have made several novel discoveries that form the background for this proposal. Preliminary studies of the anion binding machinery of NBCe1 have led to the novel finding that it functions as both an electrogenic Na+-CO32- cotransporter and an electroneutral Na+-NO3- cotransporter. Mutations in NBCe1 that cause renal tubular acidosis also inhibit NO3- transport. Based on these new findings, NBCe1 must now be considered to be a bi-functional transporter that mediates carbonate and nitrate transport in the proximal tubule, and potentially in extrarenal tissues where it is expressed. Given our findings that NBCe1 transports Na+-CO32- and Na+-NO3-, the role of the kidney and the proximal tubule in inter-organ NO3- cycling and whole body NO3- balance becomes particularly relevant both from a physiologic and clinical standpoint. The proposal will characterize the architectural basis for the function of NBCe1 as both an electrogenic Na+-CO32- cotransporter and an electroneutral Na+-NO3- cotransporter, the perturbation of these functional properties in disease, and the role of NBCe1 and the proximal tubule in NO3- transport.