Structure and Function of SWEET Sugar Transporters

 描述（由申请人提供）：糖是多细胞生物体的关键能量来源，其跨膜流出对许多生理过程至关重要，包括血糖维持和产奶。SWEET转运蛋白（SWEET transporters，SWEET）是一种新型的糖转运蛋白。SWEI也是MtN 3膜蛋白家族的原型，其包括线粒体丙酮酸载体、PQ环转运蛋白和KDEL受体等重要成员。真核SWEET及其“半转运体”细菌同系物SemiSWEET是研究膜蛋白进化中广泛观察到的复制-融合的独特模型系统。尽管SWEET在糖利用和MtN 3蛋白在线粒体功能、溶酶体氨基酸稳态和ER蛋白保留中的重要性，但我们不了解SWEET和MtN 3在分子水平上的机制。为了克服进展的主要障碍-缺乏结构框架来指导我们对运输的机械理解-我们已经解决了两种SemiSWEET蛋白质的高分辨率结构，处于两种不同的构象状态：向外开放和封闭。我们将利用这些结构数据来详细了解SWE 3的结构和功能，更广泛地说，MtN 3。具体目标1：使用X射线晶体学和生物物理学方法阐明SemiSWEET糖转运的结构基础。这些研究将有助于我们了解半乳糖转运的物理基础。具体目标2：确定真核SWEET的第一晶体结构。这些结构信息将为转运过程提供蓝图，并有助于阐明具有内部对称性的膜转运蛋白的进化。具体目标3：通过功能研究剖析SWE 3和MtN 3的转运机制。SWEET介导的运输的基本方面将被阐明，然后扩展到MtN 3家族的成员。总体影响：这项研究将揭示SWEETs转运糖的结构基础，阐明其转运机制，并加速探索MtN 3s作为治疗糖尿病，癌症和溶酶体贮积病的治疗靶点。

 DESCRIPTION (provided by applicant): Sugar is a key source of energy for multicellular organisms, and its efflux across the membrane is critical to many physiological processes, including blood glucose maintenance and milk production. SWEET transporters (SWEETs) are novel membrane proteins that mediate sugar export. SWEETs are also prototypes of the large MtN3 membrane protein clan, which includes notable members such as mitochondrial pyruvate carrier, PQ-loop transporters and the KDEL receptor. Eukaryotic SWEETs, together with their "half transporter" bacterial homolog, SemiSWEET, are a unique model system to study the widely observed duplication-fusion in membrane protein evolution. Despite the importance of SWEETs in sugar utilization and MtN3 proteins in mitochondrial function, lysosomal amino acid homeostasis, and ER protein retention, we do not understand SWEET and MtN3 mechanisms at the molecular level. To overcome a major barrier to progress-the lack of a structural framework to guide our mechanistic understanding of transport-we have solved high-resolution structures of two SemiSWEET proteins, in two distinct conformational states: outward open and occluded. We will leverage this structural data to gain a detailed understanding of the structure and function of SWEETs and, more broadly, of MtN3s. Specific Aim 1: Elucidate the structural basis of sugar transport by SemiSWEET using X-ray crystallography and biophysical methods. These studies will help us understand the physical basis of sugar transport by SemiSWEETs. Specific Aim 2: Determine the first crystal structure of a eukaryotic SWEET. This structural information will provide a blueprint for the transport process and help elucidate the evolution of membrane transport proteins with internal symmetry. Specific Aim 3: Dissect the transport mechanism of SWEETs and MtN3s through functional studies. Fundamental aspects of SWEET-mediated transport will be elucidated and then extended to members of the MtN3 clan. OVERALL IMPACT: The proposed research will reveal the structural basis of sugar transport by SWEETs, elucidate their transport mechanism, and accelerate exploration of MtN3s as therapeutic targets to treat diabetes, cancer and lysosomal storage diseases.