The role of the Chlamydia pneumoniae protein Pmp21 during infection

衣原体是重要的人类病原体。沙眼衣原体是一系列急性眼部和生殖道感染的病因，也是导致失明和输卵管性不孕的慢性疾病的病因，如沙眼和输卵管炎(1)。肺炎衣原体是一种重要的呼吸道病原体，与全世界5%至10%的社区获得性肺炎病例有关，血清患病率高达70%。(2)。衣原体具有独特的双相发育周期，在细胞外感染性初级体（EB）和细胞内非感染性网状体（RB）之间进行调节，后者在真核细胞的包涵体内复制。尽管与衣原体感染相关，但人们对其分子机制知之甚少（3,4）。在我们的RU项目中，我们专注于肺炎球菌感染周期的初始和最重要的步骤：在感染细菌粘附到人类宿主细胞并随后被人类细胞内化期间，病原体与人类宿主细胞的分子相互作用的表征。利用最近开发的酵母表面显示系统，我们确定了多态膜蛋白Pmp21作为第二种肺炎球菌粘附素。近2年的研究表明，Pmp21是一种真正的衣原体粘附素。详细的缺失和突变分析确定了2个短的重复氨基酸基序，这些基序是Pmp21与人类细胞结合所必需的。Pmp21与感染有关，因为真核细胞与抗体或重组蛋白的预孵育剂量依赖性地减少了感染。Pmp21属于一个由21个蛋白组成的蛋白家族，我们最近的数据显示，另外两个家族成员Pmp6和Pmp20对粘附和感染的建立也很重要，这表明可能整个Pmp蛋白家族都参与了肺炎原体感染的这方面。生化方法以及酵母2杂交筛选鉴定了潜在的人类pmp21相互作用蛋白。在未来，我们计划继续努力表征人类受体。进一步表征这两种新的粘附素将加深我们对Pmp蛋白家族在细菌附着和可能被人类细胞摄取中的作用的理解。在体内，Pmp21以加工形式存在，我们的第一批数据表明，这些形式相互作用，也与其他Pmp家族成员相互作用。因此，我们的目标是破译Pmp21的潜在相互作用网络，以确定其在感染过程中的作用。最后，我们还想研究Pmp蛋白家族在抗原变异中的潜在作用，这可能与免疫逃逸有关。

Chlamydiae are significant human pathogens. Chlamydia trachomatis is responsible for a spectrum of acute ocular and genital tract infections and for chronic diseases that lead to blindness and tubal-factor infertility, such as trachoma and salpingitis, respectively (1). Chlamydia pneumoniae is an important respiratory pathogen associated with 5 to 10 % of community-acquired cases of pneumonia worldwide and a seroprevalence of up to 70%. (2). Chlamydiae are characterized by a unique biphasic developmental cycle that modulates between an extracellular infectious elementary body (EB) and an intracellular noninfectious reticulate body (RB) which replicates within an inclusion in the eukaryotic cell. Despite its relevance very little is known about the molecular mechanism of a chlamydial infection (3, 4). In our RU project we focus on the initial and most important step of the C. pneumoniae infection cycle: the characterization of the molecular interaction of the pathogen with its human host cell during adhesion of the infectious bacteria to and their subsequent internalization by the human cell. Using a recently developed yeast surface display system we identified the polymorphic membrane protein Pmp21 as a second C. pneumoniae adhesin. Work of the last 2 years has revealed that Pmp21 is a bona fide chlamydia adhesin. A detailed deletion and mutational analysis identified 2 short, repetitive amino acid motifs as being necessary for Pmp21 binding to human cells. Pmp21 is relevant for the infection, as pre-incubation of eukaryotic cells with antibody or recombinant protein dose-dependently reduced infection. Pmp21 belongs to a family of 21 proteins and our recent data show that Pmp6 and Pmp20, two other family members, are also important for adhesion and establishment of infection suggesting that possibly the entire Pmp protein family might be involved in this aspect of the C. pneumoniae infection. Biochemical approaches as well as a yeast 2 hybrid screen identified potential human Pmp21-interacting proteins. In future we plan to pursue our efforts to characterize the human receptor. Further characterization of the 2 new adhesins will deepen our understanding of the role of the Pmp protein family in bacterial attachment to and potentially uptake by the human cell. In vivo Pmp21 is found in processed forms and our first data indicate that these forms interact with each other as well as with other Pmp family members. Thus, our goal is to decipher the potential interaction network of Pmp21 to define its role in the infection process. Finally we also want to study the potential role of the Pmp protein family in antigenic variation which would be relevant for immune escape.