The Biology of NBCe1 in Health and Disease

描述(由申请人提供)：SLC4家族的膜转运体介导了Cl--HCO3-和Na+驱动的Cl--HCO3-交换和Na+-HCO3-共转运(产电，电子中和)。这些转运蛋白在哺乳动物细胞生物学中的重要性被人类自发的SLC4突变和小鼠的靶向缺失引起的表型异常所突显。SLC4家族某些成员的功能和/或质膜表达异常是人类各种遗传病的原因。在已知的SLC4基因中，SLC4A4(NBCe1)和SLC4A1(AE1)在调节肾脏对碳酸氢盐的吸收、维持全身和细胞内酸碱平衡方面起着关键作用。NBCe1基因突变损害近端小管和肾外酸碱转运。在初步实验中，我们已经开始检查NBCe1功能特性的结构基础，并取得了几个新的发现，这些发现构成了这一提议的背景。对NBCe1阴离子结合机制的初步研究发现，它既是一种生电性的Na+-CO32-共转运体，又是一种电子中和性的Na+-NO3-共转运体。导致肾小管性酸中毒的NBCe1基因突变也会抑制硝酸根的转运。基于这些新的发现，NBCe1现在必须被认为是一种双功能转运蛋白，在近端小管中介导碳酸盐和硝酸盐的运输，并可能在表达它的肾外组织中发挥作用。鉴于我们的发现，NBCe1转运Na+-CO32-和Na+-NO3-，从生理和临床的角度来看，肾脏和近端小管在器官间NO_3-循环和全身NO_3-平衡中的作用变得特别重要。该提案将表征NBCe1作为生电Na+-CO32-共转运体和电子中和性Na+-NO3-共转运体的功能的结构基础，这些功能特性在疾病中的扰动，以及NBCe1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.