美国哈佛大学Daniel Kahne和Ethan C. Garner共同合作，近期取得重要工作进展。他们通过使用单分子跟踪，在活细胞中显示出瞬时脂多糖转运桥。相关研究成果2023年11月8日在线发表于《自然》杂志上。
据介绍，革兰氏阴性菌被两层膜包围，外膜的一个特殊特征是它的不对称性。它在外叶中含有脂多糖（LPS），在内叶中含有磷脂。LPS在外膜中的适当组装是细胞活力所必需的，并为革兰氏阴性菌提供对多种抗生素的内在耐药性。LPS的生物合成是在内膜中完成的，因此LPS必须被提取，穿过分离两层膜的水性周质，并穿过外膜转运，在细胞表面组装。LPS转运和组装需要七种保守和必需的LPS转运成分（LptA–G）。该系统已被提出形成一个连续的蛋白质桥，为LPS到达细胞表面提供途径，但该模型尚未在活细胞中得到验证。
通过使用单分子跟踪，研究人员表明Lpt蛋白动力学与桥模型一致。一半的内膜Lpt蛋白以桥接状态存在，桥接持续5-10秒、 表明它们的组织结构是高度动态的。LPS促进Lpt桥的形成，这表明LPS的产生可以直接与其转运偶联。最后，桥衰变动力学表明，可能存在两种不同类型的桥，其稳定性因LPS的存在（长期）或不存在（短期）而不同。
总之，这一数据支持了一个模型，在该模型中，LPS既是促进外膜组装的动态Lpt桥的底物，也是其结构组件。
附：英文原文
Title: Single-molecule dynamics show a transient lipopolysaccharide transport bridge
Author: Trk, Lisa, Moffatt, Caitlin B., Bernhardt, Thomas G., Garner, Ethan C., Kahne, Daniel
Issue&Volume: 2023-11-08
Abstract: Gram-negative bacteria are surrounded by two membranes. A special feature of the outer membrane is its asymmetry. It contains lipopolysaccharide (LPS) in the outer leaflet and phospholipids in the inner leaflet1–3. The proper assembly of LPS in the outer membrane is required for cell viability and provides Gram-negative bacteria intrinsic resistance to many classes of antibiotics. LPS biosynthesis is completed in the inner membrane, so the LPS must be extracted, moved across the aqueous periplasm that separates the two membranes and translocated through the outer membrane where it assembles on the cell surface4. LPS transport and assembly requires seven conserved and essential LPS transport components5 (LptA–G). This system has been proposed to form a continuous protein bridge that provides a path for LPS to reach the cell surface6,7, but this model has not been validated in living cells. Here, using single-molecule tracking, we show that Lpt protein dynamics are consistent with the bridge model. Half of the inner membrane Lpt proteins exist in a bridge state, and bridges persist for 5–10 s, showing that their organization is highly dynamic. LPS facilitates Lpt bridge formation, suggesting a mechanism by which the production of LPS can be directly coupled to its transport. Finally, the bridge decay kinetics suggest that there may be two different types of bridges, whose stability differs according to the presence (long-lived) or absence (short-lived) of LPS. Together, our data support a model in which LPS is both a substrate and a structural component of dynamic Lpt bridges that promote outer membrane assembly. As well as being the substrate for the lipopolysaccharide transport protein complex comprising LptA–G, lipopolysaccharide binding to Lpt proteins promotes their assembly into a bridge linking the inner and outer membranes of Gram-negative bacteria.
DOI: 10.1038/s41586-023-06709-x
Source: https://www.nature.com/articles/s41586-023-06709-x
Nature：《自然》，创刊于1869年。隶属于施普林格·自然出版集团，最新IF：69.504
官方网址：http://www.nature.com/
投稿链接：http://www.nature.com/authors/submit_manuscript.html
本期文章：《自然》：Online/在线发表
