Energy Transduction Between Membranes

描述（由申请人提供）：革兰氏阴性菌的外膜是某些营养物质扩散到质周间隙并随后转运到细胞的屏障。为了获得大量的、稀缺的、重要的营养物质，如铁铁载体和维生素B12，具有亚纳摩尔亲和力的活性转运体位于外膜。由于外膜缺乏常规的能量来源，铁铁载体和维生素B12通过外膜进入质周空间的主动运输的能量来自细胞质膜的原动力。细胞质膜上的TonB-ExbB-ExbD系统似乎可以收集质子动力，并以未知的形式将其转导到外膜活性转运体。我们的长期目标是了解大肠杆菌胞质和外膜之间依赖tonb的能量转导机制。tonB的突变使许多物种的毒性显著降低。由于铁在感染性疾病中的作用，人们普遍认为TonB系统具有开发新抗生素的新靶点的潜力。更重要的是，我们有能力对能量转导机制有更广泛的了解。目前还没有tonb依赖性能量转导的范例，但基于同源性，至少有三个这样的系统可以将pmf在几乎所有革兰氏阴性细菌中转化为有用的工作。除了ExbB/D蛋白外，还有TolQ/R蛋白（OM完整性所需）和MotA/B蛋白（运动性所需）。因此，随着广泛原理的出现，我们的结果也将对其他能量转导系统的基本知识做出重要贡献。作为具体目标，我们将解决TonB系统中的三个基本问题：细胞质膜上TonB通电的决定因素是什么，什么形式的能量被转导到外膜转运蛋白，转运蛋白是如何被TonB通电的？公共卫生相关性：几乎所有革兰氏阴性菌都使用TonB系统来规避其外膜对铁获取的限制。了解TonB系统激活跨外膜运输的分子机制将有助于未来开发阻止铁摄取的新抗生素。病原体获取铁的能力是传染病中一个重要的毒力决定因素。

DESCRIPTION (provided by applicant): The outer membranes of Gram-negative bacteria are barriers to diffusion of certain nutrients into the periplasmic space and subsequent transport into the cell. To acquire large, scarce, important nutrients such as iron-siderophores and vitamin B12, active transporters with sub-nanomolar affinities for their transport substrates are located in the outer membrane. Because the outer membrane lacks a conventional energy source, energy for active transport of iron-siderophores and vitamin B12 across the outer membrane and into the periplasmic space derives from the protonmotive force of the cytoplasmic membrane. The TonB-ExbB-ExbD system in the cytoplasmic membrane appears to harvest protonmotive force and transduce it in an unknown form to the outer membrane active transporters. Our long-term goal is to understand the mechanism of TonB-dependent energy transduction between the cytoplasmic and outer membranes of Escherichia coli. Mutations in tonB render many species significantly less virulent. Due to the role that iron availability plays in infectious disease, it is widely recognized the TonB system has potential as a novel target for the development of new antibiotics. Additional significance arises from our ability to contribute to a broad understanding of energy transduction mechanisms in general. There are currently no paradigms for TonB-dependent energy transduction and yet based on homologies, there are at least three such systems that transduce the pmf into useful work in virtually all Gram-negative bacteria. Besides the ExbB/D proteins, there are the TolQ/R proteins (required for OM integrity) and the MotA/B proteins (required for motility). Our results will therefore also contribute importantly to basic knowledge of the other energy transduction systems as broad principles emerge. As Specific Aims, we will address three fundamental problems in the TonB system: What are the determinants of TonB energization at the cytoplasmic membrane, what form of energy is transduced to the outer membrane transporters, and how does a transporter become energized by TonB? PUBLIC HEALTH RELEVANCE: Virtually all Gram negative bacteria use the TonB system to circumvent the limitations to iron acquisition posed by their outer membranes. Understanding of the molecular mechanism by which the TonB system energizes transport across the outer membranes will allow future development of new antibiotics that prevent iron uptake. The ability of pathogens to acquire iron is an important virulence determinant in infectious disease.