大肠杆菌中外源基因的表达调节

大肠杆菌已经被广泛地应用于表达各种外源基因,但基因的表达受到多种因素的调节,而且不同的外源基因在大肠杆菌中的表达效率也有很大差异。本文从转录水平调节、翻译水平调节、培养条件调节等方面综述了大肠杆菌中外源基因的表达调节,以便认识其规律,有助于使用有效的方法提高外源基因在大肠杆菌中的表达效率。     

Investigation of Proposed Ladderane Biosynthetic Genes from Anammox Bacteria by Heterologous Expression in E. coli

Ladderanes are hydrocarbon chains with three or five linearly concatenated cyclobutane rings that are uniquely produced as membrane lipid components by anammox (anaerobic ammonia-oxidizing) bacteria. By virtue of their angle and torsional strain, ladderanes are unusually energetic compounds, and if produced biochemically by engineered microbes, could serve as renewable, high-energy-density jet fuel components. The biochemistry and genetics underlying the ladderane biosynthetic pathway are unknown, however, previous studies have identified a pool of 34 candidate genes from the anammox bacterium, Kuenenia stuttgartiensis, some or all of which may be involved with ladderane fatty acid biosynthesis. The goal of the present study was to establish a systematic means of testing the candidate genes from K. stuttgartiensis for involvement in ladderane biosynthesis through heterologous expression in E. coli under anaerobic conditions. This study describes an efficient means of assembly of synthesized, codon-optimized candidate ladderane biosynthesis genes in synthetic operons that allows for changes to regulatory element sequences, as well as modular assembly of multiple operons for simultaneous heterologous expression in E. coli (or potentially other microbial hosts). We also describe in vivo functional tests of putative anammox homologs of the phytoene desaturase CrtI, which plays an important role in the hypothesized ladderane pathway, and a method for soluble purification of one of these enzymes. This study is, to our knowledge, the first experimental effort focusing on the role of specific anammox genes in the production of ladderanes, and lays the foundation for future efforts toward determination of the ladderane biosynthetic pathway. Our substantial, but far from comprehensive, efforts at elucidating the ladderane biosynthetic pathway were not successful. We invite the scientific community to take advantage of the considerable synthetic biology resources and experimental results developed in this study to elucidate the biosynthetic pathway that produces unique and intriguing ladderane lipids.     

Heterologous expression and purification of neurotoxic Hainantoxin-III in E. coli

In the present study, we used Escherichia coli to produce recombinant Hainantoxin-III (rHNTX-III), a 33-amino acid peptic toxin from the tarantula spider Haplopelma hainanum. The toxin has three pairs of disulfide bonds. A pET-HS-HNTX-III vector was constructed and transformed into the E. coli strain SHuffle^TM. rHNTX-III was expressed using auto-induction medium. After using a Ni–NTA column, the expressed fusion protein was digested using SUMO protease (ULP1) to remove the HIS–SUMO tag, and then RP–HPLC and ultrafiltration were used for further purification. Then the rHNTX-III was identified by MALDI–TOF/TOF mass spectrometry. The purified rHNTX-III was further analyzed using a whole-cell patch-clamp assay. It was shown that the rHNTX-III was able to block currents generated by human Na_v1.7 (hNa_v1.7) at an IC₅₀ of 225?nM and also have high selectivity for different voltage-gated sodium channels. Therefore, it has very similar activity to the natural one.     

人白介素6受体功能区片段在E．coli中的表达

通过ＤＮＡ体外重组技术,以ｐＥＴ－３ｂ为表达载体,构建了重组表达质粒ｐＥＴ－６Ｒ（Ｂ）和ＰＥＴ－６Ｒ（Ｂ）４,分别编码２８ｋＤ的ｈＩＬ－６Ｒ配基结合区片段及其５３ｋＤ的二联体蛋白,并为酶切分析和ＤＮＡ序列分析所证实。ＳＤＳ－ＰＡＧＥ分析表明,含有重组表达质粒的菌株可分别表达出２８ｋＤ的蛋白ｒＩＬ６Ｒ－２８和５３ｋＤ的ｒＩＬ６Ｒ－５３。重组蛋白分别占菌体总蛋白的４５％和２９％左右。重组蛋白主要以包涵体形式存在,Ｗｅｓｔｅｒｎ印迹表明重组蛋白具有ＩＬ－６Ｒ的抗原性。     

一种含ELP60基因的载体pRELPN促进大肠杆菌的外源基因的高表达

类弹性蛋白多肽（ELP）为含有人工合成的ELP60基因的表达载体pRELPN,能促使外源基因在大肠杆菌中的高表达。当ELP60在大肠杆菌表达载体pET28a的多克隆位点被克隆后,其自身的表达低,也不与目的基因构成ELP融合蛋白质,而是促进克隆在ELP60基因后的含起始密码ATG的外源目的基因独立高表达。外源目的基因表达量占宿主蛋白的20% ～ 60%,比用pET28a载体表达的外源基因表达量高2～10倍。此类表达载体pRELPN适合于表达包括抗体、抗原、酶、重组蛋白质、多肽及ELP融合蛋白质等的外源基因的独立高表达。这些结果表明,pRELPN代表了一种有效的表达载体,有助于解决在原核表达中,所受限的普通载体对外源基因低表达或不表达所导致的不能产业化的问题。     

腈水合酶NHaseK在大肠杆菌中的功能表达

腈水合酶由α亚基和β亚基组成,活化元件对其功能表达至关重要,研究腈水合酶基因簇中各元件的表达比例对酶重组表达的影响具有重要意义。以来源于Klebsiella oxytoca KCTC 1686的腈水合酶（NHaseK）为研究对象,构建了多种表达策略,以期实现α亚基、β亚基和活化元件17k差异表达。利用pETDuet-1质粒具有双T7启动子的特点,将上述基因以八种不同的组合方式分别插入于两个启动子之后。当将三段基因同时插入于第一个启动子之后时,亚基表达量均衡,比活力为0.78 U/mg蛋白,是亚基表达量比例为5：3时的124%。在此基础上,在第二个启动子之后插入活化元件基因,活化元件表达水平提升2倍,比活提升5%,为0.82 U/mg蛋白。当将α亚基和β亚基插入于不同启动子之后时,酶活仅为对照组的10%,说明NHaseK的亚基必须同时转录才可形成成熟蛋白。进一步考察质粒拷贝数对大肠杆菌表达NHaseK的影响,确定15~20的质粒拷贝数足够实现NHaseK的功能表达。结果表明,亚基的均衡表达以及活化元件的充分表达对NHaseK的重组表达具有积极作用。     

RNase A及其链亲和素融合蛋白在pET系统中的表达

在大肠杆菌中用pET28a表达载体表达重组RNaseA。变性条件下,利用His-Resin亲和纯化,得到60mg／L电泳纯的RNaseA。纯化的RNaseA复性后,利用含大量RNA分子的碱法抽提质粒为底物,测定重组RNaseA活性,与商品化的RNaseA活性相当。同时在RNaseA活性测定体系中加入4mol／L尿素会使RNA分子切割效率提高10倍左右。在此基础上,成功表达RNaseA与链亲和素(streptavidjn)的融合蛋白,经纯化复性后,该融合蛋白同时具有核酸酶、biotin结合活性,在分子生物学中具有重要的应用价值。     

Functional properties of E. coli SSB-proteins in vivo

An essential function of single-stranded DNA-binding (SSB) proteins--a defense from nuclease action, determined by their first and second domains, is realized in conditions of normal cell metabolism. With the inhibition of the replicative furcula growth and total protein synthesis (imbalance state), the SSB protein function associated with the third domain and responsible for certain modifications in DNA polymerase II activity is realized. This causes DNA degeneration and increases radiosensitivity of cells.     

Expression of spinach plastocyanin in E. coli

An expression vector designed for overexpression of plastocyanin in the periplasmic space of E. coli has been developed. The vector contains the signal peptide sequence of Pseudomonas aeruginosa azurin and the mature sequence of spinach plastocyanin. The precursor is efficiently translocated to the periplasmic space and correctly processed to mature plastocyanin. No detectable amount of plastocyanin was present in the cytoplasmic or in the membrane fraction. A large scale preparation of the recombinant plastocyanin in a 20 litre fermentor yielded approximately 30 mg of pure plastocyanin. The recombinant protein obtained from E. coli shows CD, EPR and optical properties identical to plastocyanin isolated from spinach.     

人epiregulin在大肠杆菌中的表达

利用ＲＴ－ＰＣＲ的方法首次从人肺癌细胞Ａ５４９中扩增得到了ｅｐｉｒｅｇｕｌｉｎ的ｃＤＮＡ。在３’端添加６个组氨酸密码子后将期 克隆到本实验室构建的大肠杆菌高效碱性磷酸酶分泌表达系统中进行分泌表达。表达产物经Ｎｉ柱一步分离后得到纯化。对其进行氨基酸序列分析,结果与报道的人ｅｐｉｒｅｇｕｌｉｎ的序列一致。ＭＴＴ法测定其对Ｂａｌｂ／ｃ３Ｔ３细胞有很强的促增殖作用,而对表皮癌细胞Ａ４３１有较强的抑制生长作     

Are there DNA damage checkpoints in E. coli?

The concept of regulatory ‘checkpoints’ in the eukaryotic cycle has proved to be a fruitful one. Here, its applicability to the bacterial cell cycle is examined. A primitive DNA damage checkpoint operates in E. coli such that, after exposure to ultraviolet light, while excision repair occurs, chromosome replication continues very slowly with the production of discontinuous daughter strands. The slower the rate of excision of photoproducts, the greater the delay before the normal rate of DNA replication is restored, the additional time for repair ensuring that normal survival is maintained. A model is proposed in which replication rate is controlled by the ratio of RecAcoated to uncoated single stranded regions of DNA in the replication fork. There are also two cell division inhibitors SulA (=SfiA) and SfiC under the control of the SOS system and sensitive to DNA damage, but they are irrelevant to the survival of wild-type bacteria under normal conditions. In strains where SulA and SfiC do not operate, inhibition is not influenced by the rate of excision repair and so fails one of the criteria for a DNA damage checkpoint, namely the monitoring of the DNA for the level of residual damage.     

Characterisation of atypical enteropathogenic E. coli strains of clinical origin

Background  

Enteropathogenic E. coli (EPEC) is a prominent cause of diarrhoea, and is characterised in part by its carriage of a pathogeniCity island: the locus for enterocyte effacement (LEE). EPEC is divided into two subtypes according to the presence of bundle-forming pili (BFP), a fimbrial adhesin that is a virulence determinant of typical EPEC (tEPEC), but is absent from atypical EPEC (aEPEC). Because aEPEC lack BFP, their virulence has been questioned, as they may represent LEE-positive Shiga toxin-producing E. coli (STEC) that have lost the toxin-encoding prophage, or tEPEC that have lost the genes for BFP. To determine if aEPEC isolated from humans in Australia or New Zealand fall into either of these categories, we undertook phylogenetic analysis of 75 aEPEC strains, and compared them with reference strains of EPEC and STEC. We also used PCR and DNA hybridisation to determine if aEPEC carry virulence determinants that could compensate for their lack of BFP.     

Intein 介导的重组人AR DBD的原核可溶性表达、纯化及活性鉴定

雄激素受体通过DNA结合域与效应元件结合发挥作用,在以往的研究中多采用与GST或Protein A融合的方式对雄激素受体的DNA结合域(AR DBD)进行重组表达,但获得无融合标签的纯AR DBD的操作非常繁琐。现借助内含肽介导的自剪切作用经一步亲和层析得到纯度较高的无融合标签的AR DBD,以利于对其性质和功能的研究。通过PCR方法扩增了编码人雄激素受体520~644位氨基酸的核苷酸序列,将该序列克隆入pTWIN1融合表达载体,转化大肠杆菌BL21(DE3)后对诱导温度及IPTG浓度进行优化,重组蛋白几乎全部可溶表达。将可溶性部分吸附到几丁质亲和层析柱上,通过pH诱导的内含肽自剪切作用释放出不含融合标签的重组人AR DBD蛋白,凝胶阻滞分析证明该蛋白只特异性结合保守的雄激素响应元件(ARE),具备正常的生物学活性。     

人GST-AWP1融合蛋白的原核表达及其抗体制备

为进一步研究人的一新蛋白———蛋白激酶C相关激酶 1相关蛋白 (AWP1)的结构、功能及与其相互作用的蛋白而进行GST AWP融合蛋白表达载体的构建、原核表达、纯化及其抗体的制备 .采用逆转录PCR(RT PCR)法从人ECV30 4内皮细胞中扩增AWP1cDNA编码区 ,并将其重组于谷胱甘肽硫转移酶 (GST)融合蛋白表达质粒pGEX KG中 .经酶切、序列鉴定分析后 ,用该重组质粒转化大肠杆菌BL2 1,并经异丙基 β D 硫代半乳糖苷 (IPTG)诱导产生GST AWP1融合蛋白 ,继而纯化获得了分子量约 5 6kD的融合蛋白 .将此融合蛋白免疫新西兰兔 ,经ELISA和Western印迹检测获得了效价高、免疫活性强的兔抗人多克隆抗体 .结果表明成功构建了GST AWP1融合蛋白表达载体 ,在大肠杆菌高效表达了GST AWP1融合蛋白 ,并获得高效多抗 ,为下阶段深入AWP1功能研究提供了重要的基础     

SARS病毒受体ACE2的克隆、原核表达及其功能区鉴定

ACE2(angiotensin-converting enzyme 2,ACE2)是SARS冠状病毒(severe acute respiratory syndrome associatedcoronavirus,SARS-CoV)的主要受体。此研究旨在鉴定ACE2的SARS-CoV受体功能区,为进一步阐明SARS-CoV与细胞间的相互作用机制及研制抗病毒药物等提供理论依据。利用RT-PCR从Vero-E6细胞的mRNA中分两段扩增ACE2基因,其中N端片段ACE2A1-367(102~1 210nt)不包括ACE2的酶活性位点(1 223~1 237nt,或374~378aa),而C端片段ACE2B335-805(1 101~2 524nt)包括ACE2的酶活性位点。扩增片段克隆入pMD-18T,并进行测序鉴定。进一步构建与GST基因融合表达的原核表达质粒pGEX-ACE2A与pGEX-ACE2B,IPTG诱导表达。表达的融合蛋白分子量为65kD和77kD,主要以包涵体形式存在。Western blot证实表达产物具有免疫学活性。将纯化的包涵体蛋白质复性后进行Western blot分析,证实pGEX-ACE2A表达的蛋白(~65kD)能与SARS-CoV S1蛋白特异结合,而pGEX-ACE2B表达的蛋白(~77kD)不能与S1蛋白结合。结果表明,ACE2的受体活性与酶活性位点无关,受体功能区在ACE2 N端367个氨基酸内。     

富含蛋氨酸玉米醇溶蛋白在大肠杆菌中的表达

目的:克隆玉米中富含蛋氨酸的10kD玉米醇溶蛋白,证明植物源目的基因在大肠杆菌中能够表达.方法:从玉米胚乳中克隆高蛋氨酸基因zein,通过PCR扩增zein片段,连接pGEX - 4T -1原核表达载体,转入大肠杆菌中,IPTG诱导后,HPLC测定蛋氨酸含量.结果:经PCR扩增出467bp条带,Blast分析同源性99%,经IPTG诱导进行SDS - PAGE检测,发现在36kD处出现一条明显的条带.诱导后菌体总蛋氨酸含量比正常菌体提高了9.6%.结论:证实了植物源10kD玉米醇溶蛋白在大肠杆菌中能够表达.     

高赖氨酸蛋白基因在大肠埃希菌中的表达

从四棱豆中克隆高赖氨酸蛋白基因wblys,通过PCR扩增wblys片段,转入原核表达载体pGEX-4T-1,构建pGEX-4T-1/wblys大肠埃希菌工程菌,表达重组蛋白,IPTG诱导后,发现细菌全蛋白在44 ku(含GST标签)处多出1条明显条带。HPLC检测赖氨酸含量。诱导后菌体总赖氨酸含量比正常菌体提高15.84 mg/g。在大肠埃希菌中高效表达植物源高赖氨酸蛋白基因,为该基因在益生菌中表达提供研究工作基础。     

Expression and secretion of proteins in E. coli

This review outlines approaches to the cloning and expression of proteins in Escherichia coli. The expression vectors described here (pIN-III derivatives) utilize the strong lipoprotein promoter, which is controlled by the lac-UV5 promoter-operator. These vectors provide the means for targeting a protein to any of the four subcellular compartments of the bacterial cell: cytoplasm, cytoplasmic membrane, periplasm, and outer membrane. Of particular importance is that secretion of proteins into the E. coli periplasm (using the OmpA signal peptide) is applicable for the production of both prokaryotic and eukaryotic proteins thereby enhancing protein activity and stability.