Molecular determinants of sialic acid transport in pathogenic and commensal bacteria

唾液酸是一种氨基酸，在人体组织中大量存在。在那里，它们在多种生物过程中发挥重要作用，如细胞间的通讯，细胞粘附和-识别。然而，唾液酸也是益生菌或共生菌（如脆弱拟杆菌或嗜粘阿克曼氏杆菌）的重要能量和碳来源。与此同时，人体组织中的唾液酸也会被流感嗜血杆菌等病原体利用，通过将唾液酸分子结合到其细胞壁的脂多糖中，使细菌更难被人体免疫系统识别。致病菌和共生细菌都使用特殊的转运体从人体组织中吸收唾液酸。通常使用的是所谓的TRAP（三方atp非依赖性外质）转运蛋白或MFS（主要促进剂超家族）转运蛋白。因此，对这些转运蛋白的结构和功能的研究引起了人们的高度关注。因此，本研究旨在探讨唾液酸TRAP和MFS转运体的作用机制。理想情况下，输运循环中不同中间步骤的结构将由低温电子显微镜确定。同时，通过使用特殊的构象选择性探针，单分子荧光显微镜将跟踪运输过程。通过结合这些结构和功能数据，将对细菌唾液酸转运体的功能有更深入的了解。

Sialic acids are amino sugar acids that are found in large numbers in human tissue. There, they play an important role in a variety of biological processes, such as communication between cells, cell adhesion and -recognition. However, sialic acids are also an important source of energy and carbon for probiotic or commensal bacteria such as Bacteroides fragilis or Akkermansia muciniphila. At the same time, sialic acid in human tissue is also exploited by pathogens such as Haemophilus influenzae by incorporating the molecule into the lipopolysaccharides of their cell wall, making the bacteria harder to recognize by the human immune system. Both pathogenic and commensal bacteria use special transporters to take up sialic acid from human tissue. Commonly used are so-called TRAP (tripartite ATP-independent periplasmatic) transporters or MFS (major facilitator superfamily) transporters. The structural and functional investigation of these transporters is therefore of high interest. Therefore, the aim of this proposal is to investigate the mechanism of sialic acid TRAP and MFS transporters. Ideally, structures in different intermediate steps of the transport cycle will be determined by cryo-electron microscopy. At the same time, the transport process will be followed by single-molecule fluorescence microscopy through the use of special, conformation-selective probes. By combining these structural and functional data, deep insights into the function of bacterial sialic acid transporters shall be obtained.