宿主可透過先天性免疫系統受體來識別微生物並產生防衛機制，這些微生物單元稱作病原相關分子模式 (Pathogen-associated molecular patterns, PAMPs)。當中肽聚醣 (Peptidoglycan, PGN) 為組成微生物細胞壁的獨有成分，是宿主識別的良好目標。然而肽聚醣結構存有高度變異性與複雜性，使鑑定其生物活性上有許多困難之處。透過相關代謝物的製備，將有助於了解該聚合物與宿主間的相互關係，以及相關免疫療法開發。
本論文分為三部分，首先，從三種革蘭氏陽性菌，枯草桿菌、李斯特菌與鼠李糖菌中取得肽聚醣，及細胞壁相關高分子，壁磷壁酸 (Wall teichoic acids, WTAs) 與膜磷壁酸 (Lipoteichoic acids, LTAs)，進行結構、純度與活性鑑定，以評斷取得物的品質。第二，建立一利用多種肽聚醣水解與修飾酵素作為裁切工具，與分離方法來收集其衍生片段之策略。產生約六十個不同成分的肽聚醣片段庫，並用於評估肽聚醣對宿主免疫之誘發能力。第三，評估上述取得的材料如肽聚醣以及水解片段庫，在兩個潛在的肽聚醣受體上活化能力，如在類鐸受體第二型 (Toll-like receptor 2, TLR2)，上所產生的免疫反應。
本論文利用天然微生物細胞壁為起始材料並裁切而成的肽聚醣片段庫，有別於一般化學合成方法取得的較小片段的精確分子。此全新的策略收集的肽聚醣片段庫，可拓展肽聚醣相關分子群 (Chemical space)，尋找更多有價值分子的可能性。

Microbial factors can be sensed by the host to activate proper immune responses for defense against bacteria, as pathogen-associated molecular patterns (PAMPs). Among them, peptidoglycan (PGN), a major component of bacterial cell wall is a central example of PAMPs detected by host. To identify the multifaceted functions of PGN to host, bringing this highly heterogeneous, strain-specific molecule to the molecular level is crucial.
Herein, cell wall-related products were individually extracted from Bacillus subtilis, Listeria monocytogenes, and Lactobacillus rhamnosus GG with the characterization of chemical structures and biological functions. Furthermore, a new strategy was developed to prepare PGN fragments by enzymatic degradation and fractionations. The collected fractions and cell wall-related polymers provided a collection of 60 samples and the ability to activate innate immune responses via potential pattern recognition receptors (PRRs), and toll-like receptor 2 (TLR2) was studied. In this thesis, PGNs extracted from natural sources were utilized to develop a novel strategy to prepare the derived fragments by enzymatic degradation and fractionations. The collection is different from organic synthesis which mainly focused on small and defined molecules but provides a unique PGN chemical space coverage, allowing us to identify the novel bioactive parts or molecules of PGN.

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