Laboratory Microbial Pathogenesis, Fundació d'Investigació Sanitària de les Illes Balears, Recinto Hospital Joan March, Bunyola, Spain.
PLoS Pathog. 2012;8(10):e1002978. doi: 10.1371/journal.ppat.1002978. Epub 2012 Oct 25.
Pathogenic bacteria may modify their surface to evade the host innate immune response. Yersinia enterocolitica modulates its lipopolysaccharide (LPS) lipid A structure, and the key regulatory signal is temperature. At 21°C, lipid A is hexa-acylated and may be modified with aminoarabinose or palmitate. At 37°C, Y. enterocolitica expresses a tetra-acylated lipid A consistent with the 3'-O-deacylation of the molecule. In this work, by combining genetic and mass spectrometric analysis, we establish that Y. enterocolitica encodes a lipid A deacylase, LpxR, responsible for the lipid A structure observed at 37°C. Western blot analyses indicate that LpxR exhibits latency at 21°C, deacylation of lipid A is not observed despite the expression of LpxR in the membrane. Aminoarabinose-modified lipid A is involved in the latency. 3-D modelling, docking and site-directed mutagenesis experiments showed that LpxR D31 reduces the active site cavity volume so that aminoarabinose containing Kdo(2)-lipid A cannot be accommodated and, therefore, not deacylated. Our data revealed that the expression of lpxR is negatively controlled by RovA and PhoPQ which are necessary for the lipid A modification with aminoarabinose. Next, we investigated the role of lipid A structural plasticity conferred by LpxR on the expression/function of Y. enterocolitica virulence factors. We present evidence that motility and invasion of eukaryotic cells were reduced in the lpxR mutant grown at 21°C. Mechanistically, our data revealed that the expressions of flhDC and rovA, regulators controlling the flagellar regulon and invasin respectively, were down-regulated in the mutant. In contrast, the levels of the virulence plasmid (pYV)-encoded virulence factors Yops and YadA were not affected in the lpxR mutant. Finally, we establish that the low inflammatory response associated to Y. enterocolitica infections is the sum of the anti-inflammatory action exerted by pYV-encoded YopP and the reduced activation of the LPS receptor by a LpxR-dependent deacylated LPS.
致病菌可能会改变其表面结构，从而逃避宿主的先天免疫反应。肠耶尔森氏菌（Yersinia enterocolitica）调节其脂多糖（LPS）脂质 A 结构，关键的调节信号是温度。在 21°C 时，脂质 A 为六酰化，并且可能被氨基阿拉伯糖或棕榈酸修饰。在 37°C 时，肠耶尔森氏菌表达四酰化的脂质 A，这与分子 3'-O 去酰化一致。在这项工作中，通过结合遗传和质谱分析，我们确定肠耶尔森氏菌编码一种脂 A 去酰化酶 LpxR，该酶负责在 37°C 时观察到的脂 A 结构。Western blot 分析表明，尽管 LpxR 在膜中表达，但在 21°C 时 LpxR 处于潜伏状态，未观察到脂质 A 的去酰化。氨基阿拉伯糖修饰的脂质 A 参与了潜伏状态。3D 建模、对接和定点突变实验表明，LpxR D31 减小了活性位点腔的体积，使得含有氨基阿拉伯糖的 Kdo(2)-脂质 A 无法容纳，因此不能去酰化。我们的数据表明，lpxR 的表达受 RovA 和 PhoPQ 的负调控，这对于脂质 A 与氨基阿拉伯糖的修饰是必需的。接下来，我们研究了由 LpxR 赋予的脂 A 结构可塑性对肠耶尔森氏菌毒力因子表达/功能的作用。我们提供的证据表明，在 21°C 下生长的 lpxR 突变体的运动性和真核细胞的侵袭性降低。从机制上讲，我们的数据表明，分别控制鞭毛调节子和侵袭素的调控因子 flhDC 和 rovA 的表达下调。相比之下，lpxR 突变体中 pYV 编码的毒力因子 Yops 和 YadA 的水平不受影响。最后，我们确定与肠耶尔森氏菌感染相关的低炎症反应是由 pYV 编码的 YopP 发挥的抗炎作用和由 LpxR 依赖的去酰化 LPS 引起的 LPS 受体激活减少的总和。
