沙门菌PhoP-PhoQ双组分信号转导系统

PhoP-PhoQ是调控沙门菌毒力的重要双组分信号转导系统,由组氨酸蛋白激酶PhoQ和反应调节蛋白PhoP组成。PhoP-PhoQ可调节沙门菌对Mg2+及其他周质环境的适应性,并调控沙门菌感染中毒力基因的转录和表达。PhoP-PhoQ调控的毒力基因参与沙门菌对上皮细胞的侵袭、胞内生存、对抗菌肽的抵抗反应、脂质A的修饰、Ⅲ型分泌系统效应蛋白的分泌等环节。PhoP-PhoQ还可与其他双组分信号转导系统或调节子合作,调控沙门菌的毒力。因此,PhoP-PhoQ双组分信号转导系统在沙门菌的毒力调控中发挥重要作用。     

副溶血性弧菌CalR调控vopB2的分子机制

【背景】副溶血性弧菌是一种非常重要的食源性致病菌,CalR蛋白是一种全局转录调节因子。III型分泌系统2 (Type 3 secretion systems 2 T3SS2)是副溶血性弧菌主要的毒力因子,vopB2是T3SS2中的一个关键效应蛋白。【目的】研究副溶血弧菌CalR对vopB2的转录调控机制。【方法】利用引物延伸实验鉴定vopB2及vtrA的转录起始位点,并根据产物的丰度判断CalR对靶基因的调控关系;采用实时定量RT-PCR研究靶基因mRNA在WT和ΔcalR中转录丰度,验证CalR对靶基因的转录调控关系,进一步利用LacZ实验通过比较β-半乳糖苷酶活性的差异来判定CalR对靶基因的调控关系;利用凝胶阻滞实验分析His-CalR对靶基因启动子区是否具有直接的结合作用。【结果】vopB2有两个转录起始位点A(-130和-28)且其活性受CalR的直接抑制;引物延伸和LacZ结果表明CalR对vtrA的转录并无调控作用。【结论】CalR直接抑制vopB2的转录,该抑制作用与vtrA无关联。     

细菌功能调控的重要转录因子PerR

PerR是一类存在于多种细菌中的转录因子。研究证实PerR调控的靶基因包括过氧化氢酶katA、DNA结合蛋白mrgA、铁转运调控子fur、血红素合成基因簇hemAXCDBL以及自身perR等。PerR参与的调控作用在细菌的抗氧化作用、胞内的铁离子动态平衡、以及致病菌致病作用中具有重要的意义。本综述主要从PerR调控的靶基因、参与的生理代谢作用以及PerR转录调控的分子机制等方面进行介绍,以期对我们深入了解细菌的抗逆作用机制提供参考。     

CRISPR-Cas系统调控细菌生理功能的机制研究进展

CRISPR-Cas系统是存在于部分细菌和绝大部分古细菌中的一种获得性免疫防御系统,使细菌在外源性基因入侵时具有免疫防御能力。此外,CRISPR-Cas系统对细菌自身生物膜的形成、耐药性、毒力等生理功能都有调控作用,这对于研究人员进行相关研究有着重要意义。本文以细菌CRISPR-Cas系统及其发挥免疫防御作用的相关研究为基础展开论述,重点阐述该系统对细菌生理功能的调控作用,并对其应用前景进行了展望,以期为进一步研究细菌耐药性和致病性提供新思路。     

鼠疫菌重要调控子蛋白的表达纯化及DNA结合活性分析

目的:利用大肠杆菌BL21(λDE3)的表达系统,表达7个有活性的、与鼠疫耶尔森菌(鼠疫菌)传播及致病密切相关的调控子蛋白,并对这些蛋白与DNA的结合活性进行分析,为构建鼠疫菌毒力基因转录调控网络建立分子生化实验平台。方法:通过分子克隆技术构建鼠疫菌调控子蛋白的表达菌株,所得菌株经IPTG诱导后能分别表达鼠疫菌CRP、Fur、PhoP、OxyR、OmpR、RcsB和RovA带His标签的融合蛋白;对这些蛋白与DNA的结合基序进行生物信息学预测;通过体外凝胶迁移实验验证上述蛋白与靶DNA的结合活性。结果:表达了7种有活性的鼠疫菌调控子蛋白,这些蛋白与靶基因启动子区具有体外结合活性。结论:表达的7种调控子蛋白在鼠疫菌的传播致病中有重要作用,这些调控子蛋白与DNA体外结合实验平台的建立,是构建鼠疫菌毒力基因转录调控网络的基础。     

茄科劳尔氏菌复合体毒力基因及调控网络最新研究进展

植物青枯病是一种能造成巨大经济损失的土传病害,其病原茄科劳尔氏菌复合体(Ralstonia solanacearum species complex,RSSC)能通过复杂的毒力调控网络将毒力因子合成并分泌到植物细胞胞质间或细胞质内,从而引起寄主植物发病。本文详细分析了RSSC主要的毒力基因及调控网络,包括其运动性(鞭毛,菌毛)、细菌分泌系统(T2SS、T3SS以及T6SS)、毒力调控系统(Phc、Prh、Vsr、Peh、Sol)、毒力因子(CWDEs、T3Es、EPS)、群体信号因子AHL及植物激素,总结了近年来最新的研究进展并绘制了相关网络调控模式图,以期为进一步研究RSSC的致病机理及防控研究提供参考。     

炭疽杆菌毒力基因及其表达调控的研究进展

炭疽杆菌是炭疽病的病原体,致病性主要与细菌合成毒素和英膜形成能力有关。炭疽杆菌的毒力基因表达调控涉及细菌质粒和染色体成分,细菌生长环境对毒力基因表达也有影响。     

鼠疫菌毒力调控研究

鼠疫菌通过一系列转录调控子(如CRP、PhoP、RovA和Fur)控制着一些关键毒力因子(如Pla、强毒力岛、III型分泌系统等)的基因表达。鼠疫菌可感应宿主体内信号刺激,紧密调控毒力因子的表达。在这个紧密调控过程中,调控子、毒力相关基因构成了一个动态网络。鼠疫菌在从假结核菌祖先演化的进程中,基因表达调控网络的重塑在鼠疫菌毒力进化过程中发挥着不可取代的作用。     

猪链球菌2型强毒株05ZYH33转录调控因子Rgg基因敲除突变体与野生株的基因表达差异分析

目的:为了解猪链球菌2型强毒株05Z33转录调控因子Rgg的调控作用,用基因芯片方法分析野生株与rgg基因敲除突变体之间的差异表达基因。方法:用猪链球菌2型全基因组序列点样制备芯片,将芯片运用于rgg敲除株与野生株的基因表达差异研究,采用定量real-time PCR(qRT-PCR)验证表达谱结果。结果:在突变体中共发现45个基因表达量变化在2倍以上,其中19个基因表达上调,26个基因表达下调。这些基因在细菌毒力、免疫抗原、DNA合成和修复、基础代谢和ABC转运系统等方面起着重要作用。结论:转录调控因子Rgg是一个全局调控因子,但rgg敲除后并不影响猪链球菌的毒力。     

单核细胞增生李斯特菌PrfA蛋白转录调控毒力基因表达的分子机制

单核细胞增生李斯特菌 (Listeria monocytogenes LM) 属于典型的细胞内寄生革兰氏阳性菌, 是WHO公布的四大食源性致病菌之一。LM不仅是人畜共患传染病李斯特菌病 (listeriosis) 的主要病原菌, 也是研究胞内感染和细胞介导的免疫应答的模式细菌。绝大多数LM毒力基因的转录表达受到PrfA蛋白的调控。本文简单介绍了LM侵染宿主细胞必需的毒力基因及其产物; 重点对毒力基因调节蛋白PrfA的结构和功能, PrfA调节毒力基因表达的主要方式最新进展进行了综述和讨论。     

Temperature and Mg2+ sensing by a novel PhoP-PhoQ two-component system for regulation of virulence in Edwardsiella tarda

The PhoP-PhoQ two-component system is commonly used by bacteria to sense environmental factors. Here we show that the PhoP-PhoQ system of Edwardsiella tarda detects changes in environmental temperature and Mg(2+) concentration as well as regulates the type III and VI secretion systems through direct activation of esrB. Protein secretion is activated from 23 to 35 °C or at low Mg(2+) concentrations, but it is suppressed at or below 20 °C, at or above 37 °C, or at high Mg(2+) concentrations. The effects of temperature and Mg(2+) concentration are additive. The PhoQ sensor domain has a low T(m) of 37.9 °C, and it detects temperatures through a conformational change of its secondary structure. Mutation of specific Pro or Thr residues increased the stability of the PhoQ sensor drastically, altering its temperature-sensing ability. The PhoQ sensor detects Mg(2+) concentration through the direct binding of Mg(2+) to a cluster of acidic residues (DDDSAD) and through changes that likely affect its tertiary structure. Here, we describe for the first time the use of PhoP-PhoQ as a temperature sensor for bacterial virulence control.     

Effect of PhoP-PhoQ activation by broad repertoire of antimicrobial peptides on bacterial resistance

Pathogenic bacteria can resist their microenvironment by changing the expression of virulence genes. In Salmonella typhimurium, some of these genes are controlled by the two-component system PhoP-PhoQ. Studies have shown that activation of the system by cationic antimicrobial peptides (AMPs) results, among other changes, in outer membrane remodeling. However, it is not fully clear what characteristics of AMPs are required to activate the PhoP-PhoQ system and whether activation can induce resistance to the various AMPs. For that purpose, we investigated the ability of a broad repertoire of AMPs to traverse the inner membrane, to activate the PhoP-PhoQ system, and to induce bacterial resistance. The AMPs differ in length, composition, and net positive charge, and the tested bacteria include two wild-type (WT) Salmonella strains and their corresponding PhoP-PhoQ knock-out mutants. A lacZ-reporting system was adapted to follow PhoP-PhoQ activation. The data revealed that: (i) a good correlation exists among the extent of the positive charge, hydrophobicity, and amphipathicity of an AMP and its potency to activate PhoP-PhoQ; (ii) a +1 charged peptide containing histidines was highly potent, suggesting the existence of an additional mechanism independent of the peptide charge; (iii) the WT bacteria are more resistant to AMPs that are potent activators of PhoP-PhoQ; (iv) only a subset of AMPs, independent of their potency to activate the system, is more toxic to the mutated bacteria compared with the WT strains; and (v) short term exposure of WT bacteria to these AMPs does not enhance resistance. Overall, this study advances our understanding of the molecular mechanism by which AMPs activate PhoP-PhoQ and induce bacterial resistance. It also reveals that some AMPs can overcome such a resistance mechanism.     

Constitutive expression of the phoP regulon attenuates Salmonella virulence and survival within macrophages.

The phoP genetic locus is a two-component regulatory system (phoP-phoQ) that controls the expression of genes essential for Salmonella typhimurium virulence and survival within macrophages. Strains with a phoP constitutive mutation (phenotype PhoPC) showed up to 10-fold greater expression of phoP-activated genes (pag loci) than did strains with a wild-type phoP locus (phenotype PhoP+). While the phoP constitutive mutation resulted in increased expression of pag loci, it also dramatically reduced the expression of other protein species. Comparison of the protein content of PhoP+ and PhoPC strains by two-dimensional protein gel electrophoresis demonstrated that at least 40 separate protein species were changed in expression as a result of this mutation. The PhoPC S. typhimurium were found to be attenuated for virulence and survival within macrophages. This finding suggests that a balanced PhoP-PhoQ regulatory response, which allows expression of phoP-repressed as well as -activated genes, is required for full virulence of S. typhimurium. We have further shown that small numbers of PhoPC bacteria can be used as a live attenuated vaccine to protect against mouse typhoid. As few as 15 PhoPC bacteria protected mice against challenge with 10(5) 50% lethal doses of wild-type organisms, suggesting that important protective antigens are regulated by the PhoP-PhoQ virulence regulon.     

The PhoP-PhoQ two-component regulatory system of Photorhabdus luminescens is essential for virulence in insects

Photorhabdus luminescens is a symbiont of entomopathogenic nematodes. Analysis of the genome sequence of this organism revealed a homologue of PhoP-PhoQ, a two-component system associated with virulence in intracellular bacterial pathogens. This organism was shown to respond to the availability of environmental magnesium. A mutant with a knockout mutation in the regulatory component of this system (phoP) had no obvious growth defect. It was, however, more motile and more sensitive to antimicrobial peptides than its wild-type parent. Remarkably, the mutation eliminated virulence in an insect model. No insect mortality was observed after injection of a large number of the phoP bacteria, while very small amounts of parental cells killed insect larvae in less than 48 h. At the molecular level, the PhoPQ system mediated Mg(2+)-dependent modifications in lipopolysaccharides and controlled a locus (pbgPE) required for incorporation of 4-aminoarabinose into lipid A. Mg(2+)-regulated gene expression of pbgP1 was absent in the mutant and was restored when phoPQ was complemented in trans. This finding highlights the essential role played by PhoPQ in the virulence of an entomopathogen.     

Comparison of the Pseudomonas aeruginosa and Escherichia coli PhoQ sensor domains: evidence for distinct mechanisms of signal detection

The PhoP-PhoQ two-component system is present in a number of Gram-negative bacteria where it has roles in Mg(2+) homeostasis and virulence. PhoQ is a transmembrane histidine kinase that activates PhoP-mediated regulation of a set of genes when the extracellular concentration of divalent cations is low. Divalent cations are thought to interact directly with the periplasmic PhoQ sensor domain. The PhoP-PhoQ systems of Escherichia coli and Pseudomonas aeruginosa are similar in their biological response to extracellular divalent cations; however, their sensor domains display little sequence identity. Here we have begun to explore the consequences of this sequence divergence by comparing the biophysical properties of the P. aeruginosa PhoQ sensor domain with the corresponding E. coli sensor domain. Unlike the E. coli protein, the P. aeruginosa PhoQ sensor domain undergoes changes in the circular dichroism and fluorescence spectra as well as destabilization of its dimeric form in response to divalent cations. These results suggest that distinct mechanisms of signal detection are utilized by these proteins. A hybrid protein in which the E. coli sensor domain has been substituted with the corresponding P. aeruginosa sensor domain responds normally to the presence of extracellular divalent cations in vivo in E. coli. Thus, despite apparent differences in the structural response to its stimulus, the P. aeruginosa sensor domain transduces signals to the E. coli PhoQ cytoplasmic kinase domain in a manner that mimics normal E. coli PhoQ function.     

Mutational analysis of the Escherichia coli PhoQ sensor kinase: differences with the Salmonella enterica serovar Typhimurium PhoQ protein and in the mechanism of Mg2+ and Ca2+ sensing

The PhoP-PhoQ two-component system plays a role in Mg2+ homeostasis and/or the virulence properties of a number of bacterial species. A Salmonella enterica serovar Typhimurium PhoQ sensor kinase mutant, in which the threonine at residue 48 in the periplasmic sensor domain is changed to an isoleucine, was shown previously to result in elevated expression of PhoP-activated genes and to affect mouse virulence, epithelial cell invasion, and sensitivity to macrophage killing. We characterized a complete set of proteins having amino acid substitutions at position 48 in the closely related Escherichia coli PhoQ protein. Numerous mutant proteins having amino acid substitutions with side chains of various sizes and characters displayed signaling phenotypes similar to that of the wild-type protein, indicating that interactions mediated by the wild-type threonine side chain are not required for normal protein function. Changes to amino acids with aromatic side chains had little impact on signaling in response to extracellular Mg2+ but resulted in reduced sensitivity to extracellular Ca2+, suggesting that the mechanisms of signal transduction in response to these two divalent cations are different. Surprisingly, the Ile48 protein displayed a defective phenotype rather than the hyperactive phenotype seen with the S. enterica serovar Typhimurium protein. We also describe a mutant PhoQ protein lacking the extracellular sensor domain with a defect in the ability to activate PhoP. The defect does not appear to be due to reduced autokinase activity but rather appears to be due to an effect on the stability of the aspartyl-phosphate bond of phospho-PhoP.