| Summary: | 博士 === 國立臺灣大學 === 生化科學研究所 === 104 === Helicobacter pylori, which infects approximately half of the human population, is the main cause of various gastric diseases. This pathogen is auxotrophic for cholesterol, which it converts upon uptake to various cholesteryl alpha-glucoside derivatives, including cholesteryl 6’-acyl and 6’-phosphatidyl alpha-glucosides (CAGs and CPGs). Due to a lack of sensitive analytical methods, it remains unknown whether CAGs and CPGs have distinct physiological roles and how the acyl chain components affect function. Herein we describe a metabolite-labeling method for qualitatively and quantitatively characterizing these derivatives at a femto-molar detection limit. We generated an MS/MS database of CGds that allows for profiling of all cholesterol-derived metabolites. The subsequent analysis led to the unprecedented discovery that these bacteria acquire phospholipids for CAG biosynthesis from the membrane of epithelial cells. Furthermore, we also identified the enzyme responsible for CAG biosynthesis (HP0499). The result suggested that HP0499 and the resulting products are translocated from the bacterium to the host cell via direct contact or delivery by outer membrane vesicles (OMVs) to facilitate formation of longer and/or unsaturated CAG acyl chains (also called human lipid-containing CAGs), which helped to promote lipid raft clustering, induced accumulation of integrin α5β1, and thus enhanced bacterial adhesion. This also explained the enhanced translocation of the virulence factor CagA into the host cell. These findings demonstrate how H. pylori evolves the special host/pathogen interplay to enhance bacterial virulence, and that our research pinpoints an important connection between the CAG composition and bacterial pathogenicity.
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