结核分枝杆菌ESX分泌系统研究进展

在结核分枝杆菌中存在能够使某些蛋白通过其高度疏水和通透性极差的细胞壁的分泌系统,其中ESX-1分泌系统负责ESAT-6（early secreted antigenic target of 6 kD）和CFP-10（culture filtrate protein of 10kD）的分泌．这两种蛋白能够形成1：1的二聚体结构,并且是结核分枝杆菌重要的毒力因子．近年来陆续发现其他一些蛋白也由ESX-1分泌系统所分泌．在结核分枝杆菌中还存在其他4种类似ESX-1的分泌系统ESX-2～ESX-5．ESX分泌系统也在其他革兰氏阳性菌和放线菌中被发现,有学者按照公认的术语称其为Ⅶ型分泌系统．本文综述了结核分枝杆菌ESX分泌系统的组成和分子机制,以及分泌蛋白与宿主的相互作用等方面的研究进展．     

耻垢分枝杆菌MSMEG＿4259的基因组维护功能研究

MSMEG＿4259基因及其同源基因广泛存在于分枝杆菌属中。蛋白序列分析显示,MSMEG＿4259包含DEDDh核酸外切酶结构域以及一个类似UvrC的核酸内切酶结构域,提示其可能参与DNA修复。为了探究MSMEG＿4259的生理功能,本研究利用同源重组方法在耻垢分枝杆菌(Mycolicibacterium smegmatis)构建了MSMEG＿4259基因敲除(ΔMs4259)菌株,并采用波动试验测定菌株在对数生长期以及H₂O₂处理后的利福平耐药突变频率。结果显示,ΔMs4259菌株的利福平耐药自发突变频率较野生型菌株升高1.9倍(P<0.05),该表型能够通过表达MSMEG＿4259回补。测定耐药突变菌株rpoB基因的耐药决定区域序列,发现ΔMs4259菌株的A:T>C:G突变概率较野生型菌株上升约10倍,有研究证明该突变谱是DNA氧化损伤的常见突变。实时荧光定量聚合酶链反应(real-time fluorescence quantitative polymerase chain reaction, qRT-PCR)结果显示,野...     

分枝杆菌RpsI序列差异对核糖体结构与功能的影响

核糖体结构存在动态调控,其变化与细菌发育、环境适应等过程密切相关。使用NCBI BLAST比对结核分枝杆菌(Mycobacterium tuberculosis)核糖体蛋白RpsI、RpmI和RpmJ与耻垢分枝杆菌(Mycobacterium smegmatis)相应蛋白的氨基酸序列,发现RpsI N端氨基酸序列存在较大差异。为了探究该N端序列差异对核糖体结构与功能的影响,将表达有结核分枝杆菌rpsI基因(rpsI_Rv)的质粒整合至耻垢分枝杆菌基因组中,并利用同源重组的方法敲除耻垢分枝杆菌rpsI基因,以此构建重组菌株。聚合酶链反应(polymerase chain reaction,PCR)结果表明该重组菌株构建成功。十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)显示0.5 mmol/L异丙基-β-D-硫代半乳糖苷(IPTG)于16 ℃可诱导表达RpsI_Rv。用纯化的RpsI_Rv制备特异性多克隆抗体,其效价为 1 600 000。反转录PCR 和蛋白质印迹法(Western blot)显示rpsI_Rv在重组菌株中成功表达。测定重组菌株与空载对照菌株在不同温度下的生长曲线,该重组菌株在不同温度下的生长速率未发生改变。采用通用液体倍比稀释法测定作用于核糖体不同位点的5种抗生素最小抑菌浓度(MIC₉₀),重组菌株对阿米卡星(作用于核糖体小亚基A位点的抗生素)的敏感性升高,提示分枝杆菌RpsI序列差异导致核糖体小亚基A位点附近的结构发生改变,这为分枝杆菌核糖体结构与功能的机制研究提供了数据。     

结核分枝杆菌ESX-1分泌蛋白EspB结构和功能分析

结核分枝杆菌作为肺结核病的病原菌,在人类中致死率远高于其他病原菌.结核分枝杆菌具有特殊的疏水性细胞壁结构,这种致密的细胞壁结构帮助结核分枝杆菌抵御外界环境压力和来自宿主细胞的毒素.同时,它利用特殊的分泌系统将体内的毒力蛋白输出体外,ESX-1分泌系统就是其中之一.结核分枝杆菌ESX-1系统在结核分枝杆菌进入宿主细胞吞噬小体、逃逸至细胞质以及杀死吞噬细胞这些过程中发挥重要作用.研究表明,在结核分枝杆菌内膜上存在一个由多亚基组成、旨在帮助结核分枝杆菌向外输送分泌蛋白的分泌装置.在这个分泌装置的帮助下,结核分枝杆菌重要的毒力蛋白ESAT-6跨内膜向外分泌,EspB也通过这个内膜上的分泌装置被转运至胞外.EspB存在于静置培养的结核分枝杆菌的胶囊层中,也可在振荡培养的结核分枝杆菌的培养液中被检测.通过X射线晶体衍射分析,我们解析了EspB的晶体结构,相比于其他同源结构,发现了EspB的不同构象,即EspB单体能够自组装成为七聚体的规则结构,联系其与毒力因子ESAT-6具有共分泌的特点,七聚体构象的发现为解释EspB在结核分枝杆菌向外分泌蛋白的过程中发挥的作用提供线索,即EspB具有锚定在结核分枝杆菌胶囊层中,作为运输ESAT-6的孔道而存在的可能.     

结核分枝杆菌感染对NLRP3炎性小体活化的调控作用研究进展

结核病(tuberculosis,TB)是一种主要由结核分枝杆菌(Mycobacterium tuberculosis,Mtb)感染引起的世界范围内影响广泛的细菌性疾病.巨噬细胞通过细胞表面表达的多种受体感知进而吞噬Mtb.Mtb侵染巨噬细胞时,ESX-1等分泌系统会激活以NLRP3为代表的炎性小体,并促进下游IL-1...     

肾型IBVS1基因重组BCG菌株的构建及其免疫原性研究

S1基因是传染性支气管炎病毒(IBV)的主要保护性抗原基因,应用RT-PCR技术特异地扩增嗜肾型传染性支气管炎病毒X株的S1基因,经序列分析证实为S1基因,将其连接到含有人结核分枝杆菌启动子hsp70基因和堪萨斯分枝杆菌α信号肽基因的表达载体pRR3上,从而构建了大肠杆菌-分枝杆菌穿梭表达质粒pR-α-S1,再电转化至BCG中,形成重组菌株rBCG-S1。热激后S1蛋白在耻垢分枝杆菌M.smegmatismc2155中高效表达,并且通过ELISA和Western blot检测能够被抗IBVS1蛋白的单克隆抗体识别。将106CFU的重组菌株rBCG-S1皮下注射免疫6周龄的SPF鸡,动物保护试验结果表明重组菌株rBCG-S1对鸡具有一定的免疫保护效果,能够保护SPF鸡抵抗IBVX毒株强毒攻击。血凝抑制试验表明血凝抑制抗体滴度能够显著增加。构建的重组菌株为今后开发新型鸡传染性支气管炎基因工程弱毒疫苗奠定了基础。     

miRNA中的G-四链体结构

G-四链体(G-quadruplex,G4)是由富含鸟嘌呤碱基的DNA或RNA序列组成的非典型核酸二级结构.在过去几十年中,人们着重研究了基因启动子区、UTR、端粒等常见基因功能区中的富G序列,探讨其结构与功能之间的关系.近些年,随着对非编码RNA在人类基因表达调控和疾病关系中的深入研究,非编码基因,尤其是miRNA中...     

分枝杆菌噬菌体重组系统及其应用

噬菌体是微生物遗传学研究的有力工具及源泉.分枝杆菌噬菌体也是构建分枝杆菌,尤其是结核分枝杆菌遗传研究工具的基础.目前,基于分枝杆菌噬菌体重组酶的重组系统是国际热点.总结了近年来基于分枝杆菌噬菌体Che9c重组酶gp60、gp61所构建的分枝杆菌重组工程体系及其在分枝杆菌基因组研究方面的应用,并结合实验室工作展望了其研究前景.该体系不依赖细菌自身的RecA系统,不需要限制性内切核酸酶和DNA连接酶,不需要复杂的体外操作,只需表达分枝杆菌噬菌体重组酶,从而使结核分枝杆菌基因敲除、基因敲入及点突变和构建分枝杆菌噬菌体突变株更方便.这为分枝杆菌及其噬菌体基因诱变及基因功能研究提供了迅捷的新途径.     

结核分枝杆菌同源重组基因敲除系统的构建和应用

【目的】结核分枝杆菌同源重组效率很低,突变株的构建需要半年之久。本研究的目的在于构建一种用于在结核分枝杆菌中进行基因快速敲除、且易于筛选的高效同源重组系统。【方法】野生型结核分枝杆菌转化含有SacB反向选择标记、且能诱导表达两种同源重组酶gp60和gp61的质粒pSL002。然后分别将靶基因的两个同源臂克隆入到含有hyg(潮霉素)抗性基因和gfp(绿色荧光蛋白)基因的重组质粒pSL001中,再将靶基因同源臂-loxP-hyg-gfp-loxP片段从pSL001切下,转化含有pSL002的野生型结核分枝杆菌,一步得到双交换突变株。再将含有SacB反向选择标记、且表达Cre重组酶的质粒pSL003转化入结核分枝杆菌双交换突变株中,切除两个loxP之间的hyg抗性基因和gfp基因,得到无痕缺失突变株。最后利用含有2%蔗糖的琼脂糖平板去除含有SacB反向选择标记的质粒pSL002和pSL003。【结果】在结核分枝杆菌中成功构建了高效同源重组系统,利用该系统构建了rv1364c、pstP跨膜区、pstP胞外区三个突变株,得到双交换突变株的效率为25%-62.5%,从双交换突变株得到无痕缺失突变株的效率为100%。通过gfp作为荧光标记基因,利用NightSea BlueStar蓝光手电筒和滤光眼镜,可以对平板上的基因缺失株直接进行快速判定。【结论】该同源重组系统利用gp60和gp61重组酶,在时间上将在结核分枝杆菌中无痕缺失突变株的构建从6个月缩短到3个月。这是目前为止在结核分枝杆菌中构建突变株最快且效率最高的方法,为加速分枝杆菌功能基因组的研究提供了新的遗传工具。     

PCR-SSCP检测结核分枝杆菌利福平耐药相关基因rpoB突变

目的 建立聚合酶链反应-单链构象多态性(PCR-SSCP)技术快速检测结核分枝杆菌利福平(RFP)耐药相关基因rpoB突变.方法 设计结核分枝杆菌RFP耐药相关rpoB基因PCR引物,建立PCR-SSCP技术检测临床菌株rpoB基因的突变导致的运动变位,同时采用PCR直接测序(PCR-DS)技术检测rpoB基因突变,并对上述方法检测结果进行分析和比较.结果 84株临床菌株均含有rpoB基因;PCR-SSCP和PCR-DS检测结果显示,56株RFP敏感菌株中rpoB基因分别有3株和2株检测出突变,检测特异性分别为94.6％ (53/56)和96.4％(54/56);28株RFP耐药菌株中rpoB基因分别有27株和28株发生突变,检测灵敏度分别为96.4％和100％.结论 本研究建立的PCR-SSCP技术能快速、简便、特异、敏感地检测结核分枝杆菌利福平耐药基因rpoB突变,具有临床应用前景.     

Disruption of the ESX-5 system of Mycobacterium tuberculosis causes loss of PPE protein secretion, reduction of cell wall integrity and strong attenuation

The chromosome of Mycobacterium tuberculosis encodes five type VII secretion systems (ESX-1-ESX-5). While the role of the ESX-1 and ESX-3 systems in M. tuberculosis has been elucidated, predictions for the function of the ESX-5 system came from data obtained in Mycobacterium marinum, where it transports PPE and PE_PGRS proteins and modulates innate immune responses. To define the role of the ESX-5 system in M. tuberculosis, in this study, we have constructed five M. tuberculosis H37Rv ESX-5 knockout/deletion mutants, inactivating eccA(5), eccD(5), rv1794 and esxM genes or the ppe25-pe19 region. Whereas the Mtbrv1794ko displayed no obvious phenotype, the other four mutants showed defects in secretion of the ESX-5-encoded EsxN and PPE41, a representative member of the large PPE protein family. Strikingly, the MtbeccD(5) ko mutant also showed enhanced sensitivity to detergents and hydrophilic antibiotics. When the virulence of the five mutants was evaluated, the MtbeccD(5) ko and MtbΔppe25-pe19 mutants were found attenuated both in macrophages and in the severe combined immune-deficient mouse infection model. Altogether these findings indicate an essential role of ESX-5 for transport of PPE proteins, cell wall integrity and full virulence of M. tuberculosis, thereby opening interesting new perspectives for the study of this human pathogen.     

EspD is critical for the virulence-mediating ESX-1 secretion system in Mycobacterium tuberculosis

ESAT-6 system 1 (ESX-1)-mediated secretion in Mycobacterium tuberculosis is dependent on proteins encoded by the cotranscribed espA-espC-espD gene cluster. While the roles of EspA and EspC with respect to the ESX-1 secretion system have been actively investigated, the function of EspD remains unknown. We show that EspD is secreted by M. tuberculosis, but unlike EspA and EsxA, its export does not exclusively require the ESX-1 system. Evidence for stabilization of cellular levels of EspA and EspC by EspD is presented, and depletion of EspD results in loss of EsxA secretion. Site-directed mutagenesis of EspD reveals that its role in the maintenance of cellular levels of EspA in M. tuberculosis is distinct from its facilitation of EsxA secretion. The same mutagenesis experiments have also shown that secretion of EspD is not required for the secretion of EsxA. Our findings highlight a critical and complex role for EspD in modulating the ESX-1 secretion system in M. tuberculosis.     

Genetic analysis of superoxide dismutase, the 23 kilodalton antigen of Mycobacterium tuberculosis

The gene encoding a 23 kilodalton protein antigen has been cloned from Mycobacterium tuberculosis by screening of a recombinant DNA library with monoclonal antibodies. The product of the gene has been identified as the superoxide dismutase (SOD) of M. tuberculosis on the basis of sequence comparison and by expression of the recombinant protein in a functionally active form. The derived amino acid sequence of M. tuberculosis SOD reveals a close similarity to manganese-containing SODs from other organisms, in spite of the fact that previous studies using the purified enzyme have identified iron as the preferred metal ion ligand. SOD is present in the extracellular fluid of logarithmic-phase cultures of M. tuberculosis, but the structural gene is not preceded by a signal peptide sequence. Insertion of the M. tuberculosis SOD gene into a novel shuttle vector demonstrated the mycobacteria but is ineffective in Escherichia coli.     

Overexpression of the D-alanine racemase gene confers resistance to D-cycloserine in Mycobacterium smegmatis.

D-Cycloserine is an effective second-line drug against Mycobacterium avium and Mycobacterium tuberculosis. To analyze the genetic determinants of D-cycloserine resistance in mycobacteria, a library of a resistant Mycobacterium smegmatis mutant was constructed. A resistant clone harboring a recombinant plasmid with a 3.1-kb insert that contained the glutamate decarboxylase (gadA) and D-alanine racemase (alrA) genes was identified. Subcloning experiments demonstrated that alrA was necessary and sufficient to confer a D-cycloserine resistance phenotype. The D-alanine racemase activities of wild-type and recombinant M. smegmatis strains were inhibited by D-cycloserine in a concentration-dependent manner. The D-cycloserine resistance phenotype in the recombinant clone was due to the overexpression of the wild-type alrA gene in a multicopy vector. Analysis of a spontaneous resistant mutant also demonstrated overproduction of wild-type AlrA enzyme. Nucleotide sequence analysis of the overproducing mutant revealed a single transversion (G-->T) at the alrA promoter, which resulted in elevated beta-galactosidase reporter gene expression. Furthermore, transformants of Mycobacterium intracellulare and Mycobacterium bovis BCG carrying the M. smegmatis wild-type alrA gene in a multicopy vector were resistant to D-cycloserine, suggesting that AlrA overproduction is a potential mechanism of D-cycloserine resistance in clinical isolates of M. tuberculosis and other pathogenic mycobacteria. In conclusion, these results show that one of the mechanisms of D-cycloserine resistance in M. smegmatis involves the overexpression of the alrA gene due to a promoter-up mutation.     

A unique Mycobacterium ESX-1 protein co-secretes with CFP-10/ESAT-6 and is necessary for inhibiting phagosome maturation

The ESX-1 secretion system plays a critical role in the virulence of Mycobacterium tuberculosis and M. marinum. To date, three proteins are known to be secreted by ESX-1 and necessary for virulence, two of which are CFP-10 and ESAT-6. The ESX-1 secretion and the virulence mechanisms are not well understood. In this study, we have examined the M. marinum secretomes and identified four proteins specific to ESX-1. Two of those are CFP-10 and ESAT-6, and the other two are novel: MM1553 (homologous to Rv3483c) and Mh3881c (homologous to Rv3881c). We have shown that Mh3881c, CFP-10 and ESAT-6 are co-dependent for secretion. Mh3881c is being cleaved at close to the C-terminus during secretion, and the C-terminal portion is critical to the co-dependent secretion, the ESAT-6 cellular levels, and interaction with ESAT-6. The co-dependent secretion is required for M. marinum intracellular growth in macrophages, where the Mh3881c C-terminal portion plays a critical role. The role of the co-dependent secretion in intracellular growth correlates with its role in inhibiting phagosome maturation. Both the secretion and the virulence defects of the Mh3881c mutant are complemented by Mh3881c or its M. tuberculosis homologue Rv3881c, suggesting that in M. tuberculosis, Rv3881c has similar functions.     

The ESX-5 secretion system of Mycobacterium marinum modulates the macrophage response

The ESX-5 secretion system of pathogenic mycobacteria is responsible for the secretion of various PPE and PE-PGRS proteins. To better understand the role of ESX-5 effector proteins in virulence, we analyzed the interactions of Mycobacterium marinum ESX-5 mutant with human macrophages (Mphi). Both wild-type bacteria and the ESX-5 mutant were internalized and the ESX-5 mutation did not affect the escape of mycobacteria from phagolysosomes into the cytosol, as was shown by electron microscopy. However, the ESX-5 mutation strongly effected expression of surface Ags and cytokine secretion. Whereas wild-type M. marinum actively suppressed the induction of appreciable levels of IL-12p40, TNF-alpha, and IL-6, infection with the ESX-5 mutant resulted in strongly induced production of these proinflammatory cytokines. By contrast, infection with M. marinum wild-type strain resulted in a significant induction of IL-1beta production as compared with the ESX-5 mutant. These results show that ESX-5 plays an essential role in the modulation of immune cytokine secretion by human Mphi. Subsequently, we show that an intact ESX-5 secretion system actively suppresses TLR signaling-dependent innate immune cytokine secretion. Together, our results show that ESX-5 substrates, directly or indirectly, strongly modulate the human Mphi response at various critical steps.