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

菌毛或皮利是附着在细菌表面的丝状体。这些丝是小亚基组装的结果，这些亚基聚集在一起形成不同长度和厚度的菌毛。在这些结构的顶端，坐落着另一种功能是粘附素的成分。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。在细菌病原体的背景下，它是一种重要的结构，允许细菌附着在人体细胞上，因此有助于定植和持久性过程。这一功能的一个直观的例子是尿路致病性大肠杆菌。这些病原体附着在膀胱细胞上，不会被尿流清除。由于菌毛的柔韧性，以及通过尖端的不可逆附着，它们能够抵抗水流的压力，尖端不能与宿主细胞断开。在分子水平上，菌毛在表面的发生和组装是很好理解的。它涉及一种成分，它在细菌的包膜上形成一个洞（孔），使丝状体能够到达表面。这种被称为引导器的毛孔成分存在于所有产生菌毛的细菌中。如果引座员缺席或不能正常工作，菌毛就不再产生。细菌附着在宿主细胞上的方式有很多。它还存在其他种类的细菌粘附素，其中来自百日咳杆菌的丝状血凝素（FHA）就是一个例子。B。百日咳是百日咳的病原体，FHA是参与宿主定殖的主要毒力因子。与菌毛相反，FHA粘附素不是由几个相同组分组成的多组分结构。然而，FHA能够在细胞表面形成大的螺旋结构，其将作为宿主细胞的附着装置。至于菌毛，FHA可以通过孔进入细胞表面，这与引导器不同，通常称为TpsB。TpsB组分有一个称为POTRA的区域，用于在将FHA推到细胞表面之前捕获FHA。我的实验室正在研究绿脓杆菌。这种细菌性病原体是令人恐惧的，因为它在医院感染中的流行率（世界范围内的第三大原因），并且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参与囊性纤维化个体感染的主要细菌因子，导致肺组织破坏和患者死亡。参与铜绿假单胞菌感染过程的毒力因子很多，但最近引起了很多关注的是一系列结构，称为杯，其参与慢性感染所需的菌毛的形成。我们将研究重点放在所谓的CupB系统上，更具体地说，是引导器组件CupB 3。我们发现这个引导器实际上是“经典”引导器和TpsB组件之间的混合体，因为我们在CupB 3中识别出了POTRA结构域（见上文）。我们将CupB 3 usher称为P-usher，用于包含POTRA的usher。更有趣的是，我们意识到CupB 3不仅能够组装菌毛，而且还能在细胞表面组装一种名为CupB 5的FHA样蛋白。这一发现是一个有趣的观察结果，它反映了细菌混合和匹配组分以创造新分子机器的进化机制，这进一步提高了在宿主中定植和持续的能力。在这个提议中，我们希望了解P-usher协调菌毛和CupB 5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，通过了解详细的分子机制，我们将能够设计新的抗菌剂，这将消除CupB 3功能，并有助于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.