Functional analysis of the protein machinery required for transport of lipopolysaccharide to the outer membrane of Escherichia coli
Functional analysis of the protein machinery required for transport of lipopolysaccharide to the outer membrane of Escherichia coli
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DOI：
10.1128/jb.00270-08
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发表时间：
2008-07-01
影响因子：
3.2
通讯作者：
Polissi, Alessandra
中科院分区：
文献类型：
--
作者：
Sperandeo, Paola;Lau, Fion K.;Polissi, Alessandra
脂多糖（LPS）是大多数革兰氏阴性菌外膜（OM）的重要组成部分，其结构和生物合成途径是众所周知的。然而，这种分子在细胞表面的运输和组装机制知之甚少。内膜（IM）转运蛋白MsbA负责翻转LPS穿过IM。已经鉴定了MsbA下游LPS转运机制的其他组分，包括OM蛋白复合物LptD/LptE（以前称为Imp/RlpB）、周质LptA蛋白、IM相关的细胞质ATP结合盒蛋白LptB和LptC（以前称为YrbK），这是本工作中表征的LPS转运机制的重要IM组分。在这里，我们表明，任何上述蛋白质的耗尽导致共同的表型，包括（i）在周质中存在异常的膜结构，（ii）在两个膜组分中积累的从头合成的LPS密度低于OM，和（iii）积累的修饰的LPS，这是连接到外小叶的IM的colanic酸的重复单元。我们的研究结果表明，LptA，LptB，LptC，LptD和LptE在LPS组装途径中操作，并且与其他尚未鉴定的组分一起，可能是致力于将LPS从IM的周质表面运输到OM的复合物的一部分。此外，这五种蛋白质中的至少一种在每个细胞区室中的位置表明了LPS组装途径如何在空间中组织和排序的模型。
Lipopolysaccharide (LPS) is an essential component of the outer membrane (OM) in most gram-negative bacteria, and its structure and biosynthetic pathway are well known. Nevertheless, the mechanisms of transport and assembly of this molecule at the cell surface are poorly understood. The inner membrane (IM) transport protein MsbA is responsible for flipping LPS across the IM. Additional components of the LPS transport machinery downstream of MsbA have been identified, including the OM protein complex LptD/LptE (formerly Imp/RlpB), the periplasmic LptA protein, the IM-associated cytoplasmic ATP binding cassette protein LptB, and LptC (formerly YrbK), an essential IM component of the LPS transport machinery characterized in this work. Here we show that depletion of any of the proteins mentioned above leads to common phenotypes, including (i) the presence of abnormal membrane structures in the periplasm, (ii) accumulation of de novo-synthesized LPS in two membrane fractions with lower density than the OM, and (iii) accumulation of a modified LPS, which is ligated to repeating units of colanic acid in the outer leaflet of the IM. Our results suggest that LptA, LptB, LptC, LptD, and LptE operate in the LPS assembly pathway and, together with other as-yet-unidentified components, could be part of a complex devoted to the transport of LPS from the periplasmic surface of the IM to the OM. Moreover, the location of at least one of these five proteins in every cellular compartment suggests a model for how the LPS assembly pathway is organized and ordered in space.