Functional and structural identification of peptidoglycan part structures involved in thrombospondin-1 mediated adherence of Gram-positive bacteria to host cells

肽聚糖(PG，murein)是革兰氏阴性菌和革兰氏阳性菌抵御胞质内膨胀(渗透压)所必需的外骨骼。它由寡聚-(GlcNAc-MurNAc)糖链组成，通过短肽交联形成一个复杂的三维支架(Murein)，包围并稳定细菌的细胞质膜。我们实验室的研究表明，革兰氏阳性菌如肺炎链球菌、化脓性链球菌和金黄色葡萄球菌将人糖蛋白和凝血素凝血酶反应蛋白-1(TSP-1)作为分子传感器，从而促进细菌与宿主细胞的黏附。我们可以证明，从金黄色葡萄球菌中纯化的可溶性PG天然部分结构可以抑制TSP-1介导的革兰氏阳性细菌的黏附，表明TSP-1识别细菌的PG。基于这些数据，我们计划在结构-功能关系的基础上更详细地探索PG结构在TSP-1介导的相互作用中的作用。在我们计划的研究中，我们将结合合成化学、分析和结构化学以及生化/免疫学研究的能力，探索在TSP-1介导的细菌与宿主细胞的黏附中显示生物活性的最小PG部分结构。我们将使用纯化和完全分析的天然PG部分以及合成PG部分，并根据生物活性进行化学修饰的PG结构在我们的感染检测中。预计纯化的PG一侧结构和功能设计的合成PG部分结构的结合将为PG的生物学功能提供新的见解。在长期目标上，预计这些发现将对制定对抗革兰氏阳性细菌定植的新策略产生影响，并最终导致对抗革兰氏阳性败血症的新策略。

Peptidoglycan (PG, murein) is an essential exoskeleton needed to withstand the internal cytoplasmic turgor (osmotic) pressure in both Gram-negative as well as Gram-positive bacteria. It consists of oligo-(GlcNAc-MurNAc)glycan strands that are cross-linked by short peptides to form a complex three-dimensional scaffold (murein) that surrounds and stabilizes the bacterial cytoplasmic membrane. Studies in our laboratory show that Gram-positive bacteria such as Streptococcus pneumoniae, S. pyogenes and Staphylococcus aureus engage the human glycoprotein and lectin thrombospondin-1 (TSP-1) as a molecular sensor, thereby promoting adherence of the bacteria to host cells. We could demonstrate that purified soluble PG natural part structures from S. aureus inhibits TSP-1 mediated Gram-positive bacterial adherence, indicating that TSP-1 recognizes the PG of the bacteria. Based on these data we plan to explore the role of PG structures for TSP-1 mediated interactions on the basis of a structure-function relationship in more detail. In our planned studies we will combine the capacity of synthetic chemistry, analytical and structural chemistry and biochemical/immunological studies to explore the minimal PG part structure which shows bioactivity in TSP-1 mediated adherence of bacteria to host cells. We will use purified and completely analyzed natural PG moieties as well as synthetic PG moieties and according to the biological activity chemically modified PG structures in our infection assays. It is anticipated that the combination of purified PG structures on the one side as well as functionally designed synthetic PG part structures will provide new insights into the biological function of PG. On a long term goal it is expected that these findings have an impact for the development of newer strategies against colonization by Gram-positive bacteria and will finally lead to newer strategies against Gram-positive sepsis.