Our current understanding of lipoprotein synthesis and localization in Gram-negative bacteria is based primarily on studies of Escherichia coli. Newly synthesized E. coli prolipoproteins undergo posttranslational modifications catalyzed by three essential enzymes (Lgt, LspA, and Lnt). The mature lipoproteins are then sorted to the inner or outer membrane via the Lol system (LolABCDE). Recent studies suggested that this paradigm may not be universally applicable among different classes of proteobacteria. In this study, we conducted a systematic analysis of lipoprotein processing and sorting in Helicobacter pylori, a member of the Epsilonproteobacteria that colonizes the human stomach. We show that H. pylori lgt, lspA, and lnt homologs can complement conditionally lethal E. coli mutant strains in which expression of these genes is conditionally regulated. Mutagenesis studies and analyses of conditionally lethal H. pylori mutant strains indicate that lgt and lspA are essential for H. pylori growth but lnt is dispensable. H. pylori lolA and the single lolC (or lolE) homolog are also essential genes. We then explored the role of lipoproteins in H. pylori Cag type IV secretion system (Cag T4SS) activity. Comparative analysis of the putative VirB7 homolog CagT in wild-type and lnt mutant H. pylori strains indicates that CagT undergoes amino-terminal modifications consistent with lipidation, and we show that CagT lipidation is essential for CagT stability and Cag T4SS function. This work demonstrates that lipoprotein synthesis and localization in H. pylori diverge from the canonical pathways and that lipidation of a T4SS component is necessary for H. pylori Cag T4SS activity.

中文翻译：

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幽门螺杆菌中的脂蛋白加工和分类。


我们目前对革兰氏阴性细菌中脂蛋白合成和定位的理解主要基于对大肠杆菌的研究。新合成的大肠杆菌前脂蛋白在三种必需酶（Lgt、LspA 和 Lnt）的催化下进行翻译后修饰。然后成熟的脂蛋白通过 Lol 系统 (LolABCDE) 分选到内膜或外膜。最近的研究表明，这种范式可能并不普遍适用于不同类别的变形菌。在这项研究中，我们对幽门螺杆菌的脂蛋白加工和分选进行了系统分析，幽门螺杆菌是定植于人类胃中的变形菌门的成员。我们表明，幽门螺杆菌lgt 、 lspA和lnt同源物可以补充条件致死的大肠杆菌突变菌株，其中这些基因的表达受到条件调节。对条件致死幽门螺杆菌突变株的诱变研究和分析表明， lgt和lspA对于幽门螺杆菌生长至关重要，但lnt是可有可无的。幽门螺杆菌lolA和单个lolC （或lolE ）同源物也是必需基因。然后我们探讨了脂蛋白在幽门螺杆菌Cag IV 型分泌系统 (Cag T4SS) 活性中的作用。野生型和lnt突变体中推定的 VirB7 同源物 CagT 的比较分析。 pylori 菌株表明 CagT 经历与脂化一致的氨基末端修饰，并且我们表明 CagT 脂化对于 CagT 稳定性和 Cag T4SS 功能至关重要。这项工作表明，幽门螺杆菌中的脂蛋白合成和定位与经典途径不同，并且 T4SS 成分的脂化对于幽门螺杆菌Cag T4SS 活性是必需的。