Abstract：
Lipopolysaccharides (LPS) and lipooligosaccharides (LOS) are located in the outer membrane of Gram-negative bacteria and are comprised of three distinctive parts: lipid A, core oligosaccharide (OS), and O-antigen. The structure of each region influences bacterial stability, toxicity, and pathogenesis. Here, we highlight the use of targeted activated-electron photodetachment (a-EPD) tandem mass spectrometry to characterize LPS and LOS from two crucial players in the human gut microbiota, Escherichia coli Nissle and Bacteroides fragilis. a-EPD is a hybrid activation method that uses ultraviolet photoirradiation to generate charge-reduced radical ions followed by collisional activation to produce informative fragmentation patterns. We benchmark the a-EPD method for top-down characterization of triacyl LOS from E. coli R2, then focus on characterization of LPS from E. coli Nissle and B. fragilis. Notably, a-EPD affords extensive fragmentation throughout the backbone of the core OS and O-antigen regions of LPS from E. coli Nissle. This hybrid approach facilitated the elucidation of structural details for LPS from B. fragilis, revealing a putative hexuronic acid (HexA) conjugated to lipid A.
摘要：
脂多糖（LPS）和脂寡糖（LOS）位于革兰氏阴性细菌的外膜中，由三个独特的部分组成：脂质A，核心寡糖（OS），和O-抗原。每个区域的结构影响细菌的稳定性，毒性,和发病机制。这里,我们强调使用靶向激活电子光分离（a-EPD）串联质谱来表征人类肠道微生物群中两个关键参与者的LPS和LOS，大肠杆菌尼氏和脆弱拟杆菌。a-EPD是一种混合活化方法,其使用紫外光照射以产生电荷还原的自由基离子,随后进行碰撞活化以产生信息性碎裂图案。我们将a-EPD方法作为来自大肠杆菌R2的三酰基LOS的自上而下表征的基准，然后专注于来自大肠杆菌Nissle和脆弱芽孢杆菌的LPS表征。值得注意的是,a-EPD在来自大肠杆菌Nissle的LPS的核心OS和O-抗原区的整个主链上提供广泛的片段化。这种混合方法有助于阐明来自脆弱芽孢杆菌的LPS的结构细节，揭示了与脂质A缀合的推定的己糖醛酸（HexA）。
