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周质空间以及随后转运到细胞中的屏障。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，对它们的转运底物具有亚纳摩尔亲和力的活性转运蛋白位于外膜中。由于外膜缺乏常规的能量来源，用于铁-铁载体和维生素B12主动运输穿过外膜并进入周质空间的能量来自细胞质膜的质子动力。细胞质膜中的TonB-ExbB-ExbD系统似乎收获质子动力，并以未知形式将其转移到外膜活性转运蛋白。我们的长期目标是了解大肠杆菌细胞质和外膜之间TonB依赖性能量转导的机制。tonB的突变使许多物种的毒性显著降低。由于铁的可利用性在感染性疾病中发挥的作用，人们广泛认为TonB系统有潜力成为开发新抗生素的新靶点。额外的意义产生于我们的能力，有助于广泛了解一般的能量转导机制。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使pmf在几乎所有革兰氏阴性细菌中发挥有用的作用。除了Exb B/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，我们的研究结果也将有助于重要的基本知识的其他能量转换系统的广泛原则出现。作为具体目标，我们将解决TonB系统中的三个基本问题：TonB在细胞质膜上的决定因素是什么，什么形式的能量被转导到外膜转运蛋白，以及转运蛋白如何被TonB激活？公共卫生相关性：几乎所有的革兰氏阴性细菌都使用TonB系统来规避其外膜对铁获取的限制。了解TonB系统激发跨外膜运输的分子机制将允许未来开发阻止铁吸收的新抗生素。病原体获得铁的能力是感染性疾病中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.