DpaA Detaches Braun's Lipoprotein from Peptidoglycan.
DpaA Detaches Braun's Lipoprotein from Peptidoglycan.
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DOI：
10.1128/mbio.00836-21
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发表时间：
2021-05-04
期刊：
影响因子：
6.4
通讯作者：
Vollmer W
中科院分区：
文献类型：
--
作者：
Winkle M;Hernández-Rocamora VM;Pullela K;Goodall ECA;Martorana AM;Gray J;Henderson IR;Polissi A;Vollmer W
革兰氏阴性细菌有一个独特的细胞膜，它的外膜含有内毒素，与一层薄薄的肽聚糖紧密相连。外膜和肽聚糖之间的紧密连接是维持外膜作为许多有毒分子和抗生素的不渗透屏障所必需的。肠杆菌科细菌，如大肠杆菌，通过转肽酶LdtA、LdtB和LdtC将丰富的外膜锚定脂蛋白LPP(布劳恩脂蛋白)共价连接到肽聚糖中的三肽上。LDTD和LDTE是同一个LD转肽酶家族的成员，但它们催化不同的反应，即在肽聚糖中形成3-3个交联键。大肠杆菌中第六个同系物LdtF的功能尚不清楚，尽管它已被证明在内毒素输出到外膜受到抑制的细胞中是必不可少的。我们现在证明，LdtF可以水解LPP-肽聚糖连接，将LPP从肽聚糖中分离出来，并将LdtF重新命名为肽聚糖-二氨基海松酸蛋白酰胺酶A(DPAA)。我们发现，在一定的应激条件下，LPP从肽聚糖中分离出来对细胞有利，DPAA的缺失允许LapB(YciM)基因的转座子频繁失活，其产物下调内毒素的生物合成。DPAA样蛋白具有特征的序列基序，存在于许多革兰氏阴性细菌中，其中一些没有LPP，这增加了DPAA在这些物种中有其他底物的可能性。总体而言，我们的数据表明，大肠杆菌中的LPP-肽聚糖连接比以前所认识的更具活力。
Gram-negative bacteria have a unique cell envelope with a lipopolysaccharide-containing outer membrane that is tightly connected to a thin layer of peptidoglycan. The tight connection between the outer membrane and peptidoglycan is needed to maintain the outer membrane as an impermeable barrier for many toxic molecules and antibiotics. Enterobacteriaceae such as Escherichia coli covalently attach the abundant outer membrane-anchored lipoprotein Lpp (Braun’s lipoprotein) to tripeptides in peptidoglycan, mediated by the transpeptidases LdtA, LdtB, and LdtC. LdtD and LdtE are members of the same family of ld-transpeptidases but they catalyze a different reaction, the formation of 3-3 cross-links in the peptidoglycan. The function of the sixth homologue in E. coli, LdtF, remains unclear, although it has been shown to become essential in cells with inhibited lipopolysaccharide export to the outer membrane. We now show that LdtF hydrolyzes the Lpp-peptidoglycan linkage, detaching Lpp from peptidoglycan, and have renamed LdtF to peptidoglycan meso-diaminopimelic acid protein amidase A (DpaA). We show that the detachment of Lpp from peptidoglycan is beneficial for the cell under certain stress conditions and that the deletion of dpaA allows frequent transposon inactivation in the lapB (yciM) gene, whose product downregulates lipopolysaccharide biosynthesis. DpaA-like proteins have characteristic sequence motifs and are present in many Gram-negative bacteria, of which some have no Lpp, raising the possibility that DpaA has other substrates in these species. Overall, our data show that the Lpp-peptidoglycan linkage in E. coli is more dynamic than previously appreciated.