Teasing apart the evolution of lipoprotein trafficking in gram-negative bacteria reveals a bifunctional LolA.-猫眼课题宝

DOI：

10.1073/pnas.2218473120

发表时间：

2023-02-07

期刊：

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA

影响因子：

11.1

通讯作者：

中科院分区：

综合性期刊1区

文献类型：

作者：

Smith, Hannah C.;May, Kerrie L.;Grabowicz, Marcin

关键词：

outer membrane assembly lipoprotein trafficking Escherichia coli Caulobacter vibrioides LolA

来源链接：

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9963962/

Gram-negative bacteria pose a serious healthcare threat by building an outer membrane (OM) that excludes many antibiotics. Understanding how the OM is constructed could pinpoint new avenues for antibacterial interventions. OM assembly is best characterized in Escherichia coli, and its essential assembly proteins are well conserved. A remarkable exception is LolB, which is essential for the final step of OM lipoprotein trafficking but is absent in many gram-negative species. How such bacteria traffic lipoproteins has long been unclear. We reveal that Caulobacter vibrioides LolA, which performs the preceding trafficking step, also possesses the activity of LolB. A bifunctional LolA obviates the need for LolB. Indeed, we show that an engineered E. coli LolA chimera can substitute for LolB. The outer membrane (OM) is the defining feature of gram-negative bacteria and is an essential organelle. Accordingly, OM assembly pathways and their essential protein components are conserved throughout all gram-negative species. Lipoprotein trafficking lies at the heart of OM assembly since it supplies several different biogenesis machines with essential lipoproteins. The Escherichia coli Lol trafficking pathway relies on an inner membrane LolCDE transporter that transfers newly made lipoproteins to the chaperone LolA, which rapidly traffics lipoproteins across the periplasm to LolB for insertion into the OM. Strikingly, many gram-negative species (like Caulobacter vibrioides) do not produce LolB, yet essential lipoproteins are still trafficked to the OM. How the final step of trafficking occurs in these organisms has remained a long-standing mystery. We demonstrate that LolA from C. vibrioides can complement the deletion of both LolA and LolB in E. coli, revealing that this protein possesses both chaperone and insertion activities. Moreover, we define the region of C. vibrioides LolA that is responsible for its bifunctionality. This knowledge enabled us to convert E. coli LolA into a similarly bifunctional protein, capable of chaperone and insertion activities. We propose that a bifunctional LolA eliminates the need for LolB. Our findings provide an explanation for why some gram-negative species have retained an essential LolA yet completely lack a dedicated LolB protein.