Structure elucidation and study of the biosynthesis of glycosylglycerolipids and teichoic acids of Streptococcus suis and their impact on pathogenicity

磷壁酸(Tas)是主要感染猪的人畜共患病病原菌猪链球菌细胞壁的主要成分。我们描述了其脂磷壁酸(LTA)的结构，我们可以证明猪链球菌是第一个被描述的细菌，它产生具有两种顺序连接的结构类型的LTA。一方面，我们证明了I型LTA的存在，这种LTA的特征是它的聚甘油磷酸链。另一方面，我们能够证明，在某种程度上，对于这第一个LTA，进一步复杂的糖基化构建块是重复添加的。我们已经证明在猪链球菌2型菌株中存在两种不同类别的这些复杂的LTA分子。首先，对一种不再能够糖基化其LTA的转基因菌株进行了基于细胞的分析和小鼠感染模型的实验，表明了这种菌株对致病性的高度重要性。该项目的一个目标是在其他血清型中筛选其他结构LTA变异体，这些变异体经常出现在德国和北美。此外，我们将分析序列类型(ST)1和25株血清2型菌株，其中已初步发现复杂的糖基化LTA，关于它们的LTA生物合成的选择性基因的缺失，特别是那些可能参与糖基化过程的基因。通过这一点，我们的目标是获得详细的功能洞察。到目前为止，关于壁磷壁酸(WTA)及其对猪链球菌致病作用的重要性还知之甚少。目前还没有从分子水平上证明猪链霉菌细胞壁中存在WTA。在初步工作中，我们已经能够证明在猪链球菌中存在两种不同的细胞壁附着的多糖。一种是已知的荚膜多糖，另一种聚合物显示出明显的结构特征，表明存在WTA。这种WTA的一般化学结构以及在血清2型菌株和其他血清型中推定的ST特异性变异将是该项目的一个重点。目的是了解WTA在所有菌株中是否具有完全保守的结构，或者是否可以观察到LTA所描述的ST/血清型特异性变异。猪链球菌的细胞壁含有三种不同的糖脂，但其中只有一种代表LTA的糖脂锚。其他细菌的甘油糖脂已经被描述为与C型受体Mincle相互作用。在这部分项目中，我们将系统地分析Mincle与猪链球菌甘油糖脂以及从其他细菌中分离出来的已知结构的类似分子的相互作用。综上所述，整个项目将对猪链球菌中甘油糖脂和Tas的结构和生物合成途径提供详细的见解，最终能够提出针对这种人畜共患病病原体的新的潜在药物靶点。

Teichoic acids (TAs) are essential components of the cell wall of the zoonotic pathogen Streptococcus suis that mainly infects pigs. The structure of its lipoteichoic acid (LTA) was described by us and we could show that S. suis is the first described bacterium, which produces an LTA with two sequential linked structural types. On the one hand we showed the presence of a type I LTA, which is characterized by its poly-glycerolphosphate chain. On the other hand, we were able to show that to this first LTA to some extent further complex, glycosylated building blocks are repetitively added. We already proved the presence of two different classes of these complex LTA molecules within S. suis serotype 2 strains. First experiments using cell-based assays and murine infection models with a genetically modified strain that was no longer capable of glycosylating its LTA indicated the high importance for pathogenicity of this strain. One aim of this project is the screening for other structural LTA variants within other serotypes that frequently occur especially in Germany and North America. Moreover, we will analyze the sequence type (ST) 1 and 25 strains of serotype 2, in which the complex glycosylated LTA have been initially found, with regard to their LTA biosynthesis by deletion of selective genes, especially those putatively involved in the glycosylation process. By this, we aim to gain detailed functional insights. Not much is known about the wall teichoic acid (WTA) and its importance for pathogenicity of S. suis to date. The proof of the presence of a WTA in the S. suis cell wall on the molecular level has not been done yet. In preliminary work, we have been able to show the presence of two distinct cell-wall attached polysaccharides in S. suis. One is the already known capsular polysaccharide, the other polymer displays structural features clearly pointing towards the existence of a WTA. The general chemical structure of this WTA as well as putative ST-specific variants in serotype 2 strains and in other serotypes will be one focus point of this project. The aim is to unravel if the WTA has a completely conserved structure among all strains or if ST-/serotype-specific variants as described for the LTA can be observed. The cell wall of S. suis contains three different glycoglycerolipids, but only one of these represents the glycolipid anchor of the LTA. Glycoglycerolipids of other bacteria have already been described to interact with the C-type receptor Mincle. In this part of project, we will systematically analyze the interaction of Mincle with S. suis glycoglycerolipids and similar molecules of known structure isolated from other bacteria. In summary, the whole project shall provide detailed insights into the structure and biosynthesis pathways of glycoglycerolipids and TAs in S. suis, to be finally able to propose new potential drug targets against this zoonotic pathogen.