Fujimoto Yukari, Tanaka Katsunori, Shimoyama Atsushi, Fukase Koichi
Department of Chemistry, Graduate School of Science, Osaka University, Machikaneyama, Toyonaka, Osaka, Japan.
Methods Enzymol. 2010;478:323-42. doi: 10.1016/S0076-6879(10)78016-2.
In this chapter, we describe synthetic studies on partial structures of lipopolysaccharide (LPS) and peptidoglycan (PGN), which work as tags for nonself recognition in innate immune system. Our previous studies demonstrated that lipid A is the endotoxic principle of LPS. The synthetic homogeneous preparations have enabled not only precise structure-activity relationships, but also recognition mechanisms of LPS with innate immune receptor complexes, including the TLR4/MD-2 complex, to be studied. Synthetic studies of lipid A and Kdo-lipid A from parasitic Helicobacter pylori revealed their low inflammatory activities, suggesting the molecular evolution to escape from the host immune system. A synthetic study of the partial structures of PGN has also contributed to the understanding of the innate immune mechanism. The biological activities of the synthetic fragments have revealed that the intracellular receptor Nod2 recognizes partial structures containing the muramyl dipeptide (MDP) moiety. The PGN of Gram-negative bacteria and some Gram-positive bacteria contain meso-diaminopimelic acid (meso-DAP), and recent studies have revealed that the intracellular receptor Nod1 recognizes DAP-containing peptides. We have synthesized DAP-containing PGN fragments, including the first chemical synthesis of tracheal cytotoxin (TCT). The ability of these fragments to stimulate human Nod1 as well as differences in Nod1 recognition for various synthesized ligand structures was elucidated. Cell-surface glycans such as N-glycans and O-glycans on glycoproteins and glycoconjugates work as signaling molecules for self-recognition and control immune system. Our new strategy using glycan-imaging in whole-body system is expected to unveil the dynamics of glycans in the body. Positron emission tomography (PET) is a noninvasive method that visualizes the locations and levels of radiotracer accumulation. We developed the facile labeling of peptides and proteins for PET imaging. The labeled glycoproteins and glycoclusters were then subjected to PET imaging in order to examine their in vivo dynamics, visualizing the differences in the circulatory residence of glycoproteins and glycoclusters in the presence or absence of sialic acid residues.
在本章中，我们描述了对脂多糖（LPS）和肽聚糖（PGN）部分结构的合成研究，它们在先天免疫系统中作为非自我识别的标签发挥作用。我们之前的研究表明，脂质A是LPS的内毒素成分。合成的均一制剂不仅使精确的构效关系研究成为可能，还能对LPS与包括TLR4/MD-2复合物在内的先天免疫受体复合物的识别机制进行研究。对来自寄生性幽门螺杆菌的脂质A和Kdo-脂质A的合成研究揭示了它们较低的炎症活性，这表明其在分子进化上以逃避宿主免疫系统。对PGN部分结构的合成研究也有助于理解先天免疫机制。合成片段的生物学活性表明，细胞内受体Nod2识别含有胞壁酰二肽（MDP）部分的结构。革兰氏阴性菌和一些革兰氏阳性菌的PGN含有内消旋二氨基庚二酸（meso-DAP），最近的研究表明，细胞内受体Nod1识别含DAP的肽。我们已经合成了含DAP的PGN片段，包括气管细胞毒素（TCT）的首次化学合成。阐明了这些片段刺激人Nod1的能力以及Nod1对各种合成配体结构识别的差异。糖蛋白和糖缀合物上的细胞表面聚糖，如N-聚糖和O-聚糖，作为自我识别的信号分子并调控免疫系统。我们在全身系统中使用聚糖成像的新策略有望揭示体内聚糖的动态变化。正电子发射断层扫描（PET）是一种可视化放射性示踪剂积累位置和水平的非侵入性方法。我们开发了用于PET成像的肽和蛋白质的简便标记方法。然后对标记的糖蛋白和糖簇进行PET成像，以检查它们在体内的动态变化，可视化在有或没有唾液酸残基的情况下糖蛋白和糖簇循环停留的差异。
