Helicobacter pylori gamma-glutamyltransferase relates to proteomic adaptations important for colonization

Helicobacter pylori γ-glutamyltransferase (gGT) is a conserved virulence factor promoting bacterial colonization and immune tolerance. Although some studies addressed potential mechanisms explaining its function, the supportive role of gGT for in-vivo colonization remains unclear. In addition, it is unknown how differences in gGT expression observed for different strains may lead to compensatory mechanisms to ensure infection and persistence. Hence, it is of high importance to understand more profoundly the in-vivo function of this enzyme. In this study, we assessed acid survival under physiologic conditions mimicking the human gastric fluid and elevated the pH in the murine stomach prior to H. pylori infection to link gGT-mediated acid resistance to colonization. Furthermore, by comparing protein expression levels between wildtype and gGT-deficient H. pylori isolates before and after infecting mice, we systematically investigated proteomic adaptations of gGT-deficient bacteria during infection. Our data indicate that gGT plays a crucial role in sustaining urease activity in acidic environments, thereby supporting bacterial survival and successful colonization. The absence of gGT triggers the expression of proteins involved in nitrogen and iron metabolism, indicating a potential functional role of gGT in these metabolic pathways. Moreover, we observed an impaired growth of gGT-deficient strains in iron-restricted medium. In addition, the absence of gGT during infection leads to a significant overexpression of H. pylori adhesins and flagellar proteins, resulting in increased motility and adhesion capacity. In summary, we identified gGT-dependent mechanisms conferring a growth advantage to the bacterium in the gastric environment, which renders gGT a valuable target for the development of new treatments against H. pylori infection.

幽门螺杆菌（Helicobacter pylori）γ-谷氨酰转移酶（γ-glutamyltransferase，gGT）是一种保守的毒力因子，可促进细菌定植与免疫耐受。尽管已有部分研究阐明了其发挥功能的潜在机制，但gGT在体内定植中的支持作用仍未明确。此外，目前尚不明确不同菌株中gGT表达的差异如何引发代偿机制，以保障感染的建立与持续。因此，深入解析该酶的体内功能具有重要意义。
本研究中，我们在模拟人体胃液的生理条件下评估了细菌的酸存活能力，并在幽门螺杆菌感染前升高小鼠胃部的pH值，以将gGT介导的酸抗性与定植过程联系起来。此外，我们通过比较感染小鼠前后野生型与gGT缺陷型幽门螺杆菌分离株的蛋白质表达水平，系统解析了感染过程中gGT缺陷型细菌的蛋白质组适应性变化。
我们的研究数据表明，gGT在酸性环境中对维持脲酶活性具有关键作用，进而助力细菌存活与成功定植。gGT的缺失会诱导参与氮代谢与铁代谢的蛋白质表达上调，提示gGT在这些代谢通路中可能发挥功能性作用。此外，我们观察到gGT缺陷型菌株在缺铁培养基中的生长受到损害。另外，感染过程中gGT的缺失会导致幽门螺杆菌黏附素与鞭毛蛋白的显著上调表达，进而提升细菌的运动与黏附能力。
综上，我们鉴定出了可使细菌在胃部环境中获得生长优势的gGT依赖型机制，这使得gGT成为开发抗幽门螺杆菌感染新型治疗手段的极具价值的靶点。