Cell wall synthetic lipid microdomains: composition and mechanism of formation

抗生素在医疗保健和农业领域的广泛使用导致了对大多数甚至所有抗生素具有耐药性的细菌菌株的出现。因此，细菌感染再次成为严重的健康问题，并成为卫生保健系统日益沉重的经济负担。为了遏制这一趋势，研究和开发新的抗生素是当务之急。我们现在需要确定不容易受到现有耐药机制影响的新型抗生素，并将我们的长期努力引向本质上具有较低耐药风险的抗生素。从历史上看，我们最成功的抗生素类别是由其他生物体产生的天然化合物，以抵消其环境中的细菌。这些抗生素类别是基于良好的抗菌活性而确定的，并且通常具有复杂的抗菌作用模式，同时抑制多个细胞系统。近几十年来，开发新抗生素的努力一直以靶标驱动的方法为主，这种方法首先确定一个理论上良好的单一抗生素靶标，然后筛选针对它的特定抑制剂。由于对单一作用模式抗生素的耐药性发展速度很快，这种方法在很大程度上失败了。因此，我们现在需要重新关注那些不通过单一抑制机制起作用的抗生素。以细菌细胞膜为靶点的化合物在自然界中被广泛用作抗菌剂。这些分子是由其他细菌、真菌、植物和动物产生的，用来对抗不需要的细菌。与我们目前的抗生素相比，这种进化上非常成功的策略有两个关键优势。首先，细胞靶标是膜脂，而不是抑制基因编码的靶标，如蛋白质或核糖体。因此，改变靶标从而阻止结合的突变不容易出现。其次，细胞膜的破坏同时抑制了大量与膜相关的细胞过程，从而使细菌难以进化出有意义的防御。细胞膜靶向抗生素破坏的一个关键细胞过程是细胞壁的合成，细胞壁是一种坚硬的结构，包围细胞并为其提供物理稳定性。对细胞壁合成的干扰为膜靶向抗生素提供了导致细胞不可逆解体的能力，这一过程被称为细菌溶解。因此，膜靶向抗菌剂杀死细菌的速度非常快，而且耐药性发展的速度非常低，甚至无法检测到。细菌细胞壁合成机制对膜靶向抗生素敏感的原因仍然难以捉摸。最近，我们发现负责细胞壁合成的蛋白质在其膜周围（脂质结构域）诱导一个特定区域，其性质和组成与其余膜不同。这些脂质结构域是膜靶向抗生素的首选靶点，因此提供了细胞壁合成被有效抑制的第一个合理解释。在这个项目中，我们将确定与细胞壁合成机制相关的脂质结构域被诱导的机制，并描述它们的详细组成。这对于了解细菌如何合成其保护细胞壁的包膜，以及膜靶向抗菌剂如何通过破坏其合成来杀死细菌非常重要。通过直接洞察其效力的机制，我们的研究将指导利用这一细胞弱点的新型膜靶向抗生素的设计和开发。

The wide use of antibiotics in healthcare and agriculture has caused the appearance of bacterial strains that are resistant against most or even all antibiotics. As a result, bacterial infections have re-emerged as a serious health concern, and an increasing financial burden for the healthcare systems. To counteract this trend, research and development of new antibiotics is a top priority. We now need to identify new classes of antibiotics that are not readily compromised by existing resistance mechanisms, and to direct our long-term efforts towards antibiotics with an intrinsically lower risk of resistance development. Historically, our most successful classes of antibiotics have been natural compounds produced by other organisms to counteract bacteria in their environment. These antibiotic classes were identified based on good antibacterial activity, and usually feature a complex antibacterial mode of action with several cellular systems inhibited at the same time. In recent decades, efforts to develop new antibiotics have been dominated by a target-driven approach, which first identifies a single, theoretically good antibiotic target, and then screens for specific inhibitors against it. This approach has largely failed due to the rapid rate of resistance development against single mode-of-action antibiotics. Consequently, we now need to re-focus on antibiotics that do not act by a single inhibitory mechanism. Compounds that target bacterial cell membranes are widely used in nature as antimicrobials. These molecules are produced by other bacteria, fungi, plants and animals to combat undesired bacteria. This evolutionally highly successful strategy has two crucial advantages over our current antibiotics. Firstly, instead of inhibiting gene-encoded targets such as proteins or ribosomes, the cellular targets are membrane lipids. Consequently, mutations that modify the target and thereby prevent the binding do not easily emerge. Secondly, the disruption of the cell membrane simultaneously inhibits a large number of membrane-associated cellular processes, thus making it difficult for bacteria to evolve a meaningful defense. One crucial cellular process disrupted by membrane-targeting antibiotics is the synthesis of cell wall, a rigid structure that encloses the cell and provides it with physical stability. The interference with the cell wall synthesis provides membrane-targeting antibiotics the ability to cause irreversible disintegration of the cell, a process termed bacteriolysis. Consequently, membrane-targeting antimicrobials kill bacteria very rapidly, and the rate of resistance development is either remarkably low or even undetectable. The reason why the bacterial cell wall synthesis machinery is sensitive to membrane-targeting antibiotics has remained elusive. Recently, we showed that proteins responsible for the cell wall synthesis induce a specific area in their membrane surrounding (lipid domain) that differs from the remaining membrane in its properties and composition. Such lipid domains are preferred targets for membrane-targeting antibiotics, hence providing the first plausible explanation why cell wall synthesis is efficiently inhibited. In this project, we will identify the mechanism through which the lipid domains associated with the cell wall synthesis machinery are induced, and characterise their detailed composition. This is important in order to understand how bacteria synthesise their protecting cell wall envelope, and how membrane-targeting antimicrobials kill bacteria by disrupting its synthesis. By providing direct insight into the mechanisms underpinning their potency, our research will guide the design and development of novel membrane-targeting antibiotics that exploit this cellular weak point.