The P-Usher: A mix and match secretion machine for the assembly of bacterial cell surface appendages.

菌毛是附着在细菌表面的细丝。这些细丝是小的亚单位聚集在一起形成不同长度和厚度的被毛的结果。在这些结构的顶端，有另一种成分，其功能是粘附素。这种粘附素能够将细菌与不同类型的表面/组织牢固地连接在一起。在细菌病原体的背景下，它是一个重要的结构，它允许细菌附着在人体细胞上，从而有助于定植和持续过程。尿路致病性大肠杆菌就是这个功能的一个直观例子。这些病原体附着在膀胱细胞上，不会被尿液排出。它们可以抵抗水流的压力，这要归功于菌毛的柔韧性，以及通过尖端的不可逆附着，而尖端无法与宿主细胞断开。在分子水平上，人们已经很好地了解了表面毛层的发生和组装。它包括一种成分，它在细菌的包膜上形成一个孔（孔），使细丝能够进入表面。这种被称为usher的孔隙成分存在于所有产生菌毛的细菌中。如果引子缺失或功能不正常，毛毡就不再形成。细菌附着在宿主细胞上的方式有很多。它存在其他种类的细菌黏附素，其中丝状血凝素（FHA）从百日咳博德泰拉是一个例子。百日咳是百日咳的病原体，FHA是参与宿主定植的主要毒力因子。与纤维相反，FHA粘连素不是由几个相同的成分组成的多组分结构。然而，FHA能够在细胞表面形成一个大的螺旋结构，这将作为附着在宿主细胞上的装置。至于被毛，FHA可以通过一个孔进入细胞表面，这个孔不同于usher，通常被称为TpsB。TpsB组件有一个称为POTRA的区域，用于在将FHA推出细胞表面之前捕获FHA。我的实验室正在研究铜绿假单胞菌。这种细菌性病原体令人恐惧，因为它在医院感染中的流行（世界第三大原因），因为它对住院患者的发病率和死亡率有很高的影响。铜绿假单胞菌也被认为是囊性纤维化个体感染的主要细菌，导致肺组织破坏和患者死亡。参与P. aeruginosa感染过程的毒力因子很多，但最近人们对一系列名为Cup的结构给予了大量关注，这些结构参与了慢性感染所需菌毛的形成。我们的研究重点是所谓的cupbb系统，特别是引导组件CupB3。我们发现这个引子实际上是“经典”引子和TpsB组件之间的混合物，因为我们在CupB3中发现了一个POTRA域（见上文）。我们把CupB3引座器称为p引座器，即含有potra的引座器。更有趣的是，我们意识到CupB3不仅能够组装毛，而且还能在细胞表面组装一种叫做CupB5的类似FHA的蛋白质。这一发现是一个有趣的观察结果，它反映了细菌通过混合和匹配成分来创造新的分子机器的进化机制，从而进一步提高了在宿主体内定植和生存的能力。在这个提议中，我们想要了解P-usher协调毛膜和CupB5粘附素组装的机制。我们还想了解这种独特的细菌机器如何有助于优化铜绿假单胞菌的定植过程。最后，通过详细的分子机制了解，我们将有可能设计新的抗菌剂，以消除CupB3的功能，帮助对抗铜绿假单胞菌感染。

Fimbriae or pili are filaments attached to the surface of bacteria. These filaments are the result of the assembly of small subunits that come together to form fimbriae of various length and thickness. At the tip of these structures, sits another component whose function is an adhesin. This adhesin is able to connect firmly the bacterium with different types of surface/tissue. In the context of bacterial pathogens, it is an important structure, which allows bacteria to attach to human cells and therefore contribute to the colonization and persistence process. A visual example for this function is given with uropathogenic Escherichia coli. These pathogens are attached to bladder cells and are not eliminated by the urine flow. They resist the pressure of the stream thanks to the flexibility of the fimbriae, and the irreversible attachment via the tip, which could not be disconnected from the host cell. At a molecular level, the occurrence and assembly of the fimbriae at the surface is well understood. It involves a component, which forms a hole (pore) in the envelope of the bacterium, to give the filament access to the surface. This pore component, called the usher, is found in all bacteria, which produce fimbriae. If the usher is absent or does not function properly, fimbriae are not made anymore. Means by which bacteria attach to host cells are numerous. It exists other kinds of bacterial adhesins, of which the filamentous hemagglutinin (FHA) from Bordetella pertussis is an example. B. pertussis is the agent of the whoopping cough and FHA is a major virulence factor involved in host colonization. In contrast to fimbriae the FHA adhesin is not a multi-component structure made of several identical components. Nevertheless, FHA is capable of making a large and helical structure at the cell surface, which will act as an attachment device to host cells. As for fimbriae, FHA can access the cell surface thanks to a pore, which is different from the usher and commonly named TpsB. The TpsB component has a region called POTRA, which is used to fish FHA, before pushing it out to the cell surface. My laboratory is working on Pseudomonas aeruginosa. This bacterial pathogen is feared because of its prevalence in nosocomial infections (third cause world-wide), and because it has a high impact on the morbidity and mortality of hospitalized patients. P. aeruginosa is also known as the main bacterial agent involved in infection of cystic fibrosis individuals, resulting in destruction of lung tissues and patient death. The virulence factors involved in the P. aeruginosa infection process are numerous, but recently a lot of attention has been given to a series of structure, named Cup, which are involved in the formation of fimbriae required in chronic infection. We focused our study on the so-called CupB system and more particularly the usher component CupB3. We discovered that this usher is in fact a hybrid between a 'classical' usher and a TpsB component, since we identified a POTRA domain (see above) in CupB3. We called the CupB3 usher a P-usher for POTRA-containing usher. More interestingly, we realized that CupB3 is not only able to assemble fimbriae, but it also assembles a FHA like protein called CupB5 at the cell surface. Such discovery is an intriguing observation, which reflects evolutionary mechanisms by which bacteria mix and match components to create new molecular machines, which give further improved capacity in colonising and persisting within the host. In this proposal, we want to understand the mechanism by which the P-usher coordinates the assembly of fimbriae and the CupB5 adhesin. We also want to understand how this unique bacterial machine contributes to optimize the colonization process of P. aeruginosa. Finally, by understanding the detailed molecular mechanism, we will be in a situation to design new antimicrobials, which will abolish the CupB3 function and help fighting against P. aeruginosa infection.