Crossing the periplasmic void, elucidating the mechanisms of phospholipid transport in Gram-negative bacteria

微生物，特别是革兰氏阴性菌对抗菌素疗法的耐药性日益增强，是21世纪全球公共卫生面临的最大威胁之一。事实上，仅在欧洲，可避免的25,000例死亡和250万天住院被认为与抗药性的上升直接相关，总共造成12亿英镑的损失。英国首席医疗官Sally Davies教授最近将抗菌素耐药性称为“灾难性的威胁”，并建议如果不开发新的抗生素，小手术可能会致命。然而，世界卫生组织最近的一份报告强调了正在开发的新型抗生素的惊人缺乏，并发现大多数正在开发的新药都是对现有抗生素类别的修改。开发新的抗菌药物需要深入了解革兰氏阴性菌的功能和维持体内平衡。选择细菌中的哪个系统作为目标是药物开发计划的一个核心概念。其中一个有吸引力的目标是细菌的细胞包膜，其产生和维持的机制可能是产生新型抗菌剂的关键。所有革兰氏阴性菌都有两层膜（由脂质组成）包裹着细胞，被称为周质的空间隔开。这两层膜的外层保护细菌免受环境的影响，并通过形成半透层来控制分子进出细胞的运动，从而代表了细菌的第一道防线。此外，该膜内的蛋白质对细菌的发病和耐药性至关重要。因此，它们被视为微生物战争的工具，介导负责感染和疾病进展的过程。通过鉴定新化合物来防止这种膜的形成可能会导致下一代抗菌剂的开发。最近，在细胞膜内外都发现了一种被称为Mla通路的蛋白质网络，它被确定为负责脂质在细胞膜之间的运输。最近的证据表明，Mla系统对于维持外膜的结构和功能都很重要，并且可以通过从内膜转移脂质来补充其含量。因此，该系统已被确定为膜功能的关键调节剂。因此，了解该系统的工作原理至关重要，因为设计抑制Mla途径活性的新化合物可能会破坏外膜结构，从而抑制革兰氏阴性菌的许多基本生理、致病和耐药功能。在这个研究项目中，我们计划描述Mla途径在内外膜之间运输脂质所进行的机制过程，我们将确定不同类型的脂质是如何转移的，以及它们如何从内膜中去除的细节，从而提供有价值的机制见解，这将有助于发现分子抑制剂和新型抗菌剂。

The ever-increasing resistance of microorganisms to antimicrobial therapies, in particular for Gram-negative bacteria, represents one of the greatest threats to global public health of the 21st century. In fact, in Europe alone, an avoidable 25,000 deaths and 2.5 million days in hospital are thought to be directly related to this rise in resistance, totalling a cost of £1.2 Billion. England's Chief Medical Officer, Professor Dame Sally Davies recently termed antimicrobial resistance "a catastrophic threat", and suggested that without the development of new antibiotics minor operations may become deadly. However, a recent report by the WHO highlighted the alarming lack of new antibiotics under development and found most new drugs in the pipeline to be modifications of existing classes of antibiotics. The development of new antimicrobial agents requires an in depth understanding of how Gram-negative bacteria function and maintain homeostasis. Selecting which of the systems in the bacteria to target signifies a central concept of the drug development programme. One such attractive target is the bacterial cell envelope, with the mechanisms involved in its production and maintenance perhaps holding the key to generating novel antimicrobials. All Gram-negative bacteria possess two membranes (made of lipids) that enclose the cell, separated by a space known as the periplasm. The outer of the two membranes protects the bacterium from the environment and represents its first line of defence by forming a semi-permeable layer through which it controls the movement of molecules into and out of the cell. Furthermore, proteins within this membrane are essential for bacterial pathogenesis and drug resistance. As such they are viewed as the instruments of microbial warfare, mediating the processes responsible for infection and disease progression. Preventing the formation of this membrane through the identification of new compounds could lead to the development of the next generation of antimicrobials.Recently a network of proteins found at both the outer and inner membranes, known as the Mla pathway, was identified as being responsible for the transport of lipids between the two membranes. Recent evidence suggests that the Mla system is important for maintaining both the structure and the function of the outer membrane and can replenish its lipid content by transferring it from the inner membrane. Consequently, the system has been identified as a key modulator of membrane function. It is therefore of critical importance to understand how this system works, as the design of new compounds that inhibit the activity of the Mla pathway could potentially disrupt outer membrane structure and thus inhibit many essential physiological, pathogenic and drug resistance functions of Gram-negative bacteria.In this research project we plan to characterise the mechanistic processes the Mla pathway undertakes in order to transport lipids between the inner and outer membranes, we will identify how the different types of lipids are transferred and the details behind how they are removed from the inner membrane, thus providing valuable mechanistic insights that will aid in the discovery of molecular inhibitors and new classes of antimicrobial agents.