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1.
克隆了近平滑假丝酵母(Candida parapsilosis)(R)-羰基还原酶基因rcr,构建胞外表达工程茵Escherichia coli BL21(DE3)/pET20b-rcr,实现了(R)-羰基还原酶在大肠杆菌中高效外泌表达,周质空间和发酵液酶的比活力分别达0.68 U/mg和0.26 U/mg,与大肠杆菌的胞内体系重组酶相比,酶的比活力提高了近两倍。为了更好地促进该重组酶的外分泌于大肠杆菌细胞外,通过添加温和型化学渗透剂甘氨酸,改善细胞壁的透性,(R)-羰基还原酶的活力提高至1.99 U,与添加甘氨酸前相比,酶活力提高了12.4倍,比活提高了4.3倍。浓缩后的发酵液催化2-羟基苯乙酮,产生(R)-苯基乙二醇,产率为88.1%,e.e.值为93.9%。与胞内重组酶相比,产率和光学纯度分别提高了44.4%和15.9%。本研究通过构建(R)-羰基还原酶的大肠杆菌分泌表达体系,大幅度提高了(R)-羰基还原酶的比活和生物转化手性醇的效率。  相似文献   

2.
目的:通过优化PET11b-s TNFαRI 5'mRNA翻译起始区(TIR)二级结构从而提高可溶性肿瘤坏死因子I型受体(sTNFαRI)在大肠杆菌[E.coli BL21(DE3)]中的表达水平。方法:通过对PET11b-s TNFαRI mRNA 5'端TIR区二级结构的自由能及核苷酸位置熵分析,设计相应的引物对mRNA 5'翻译起始区(TIR)相应密码子进行突变,从而使核糖体结合位点(RBS)及起始密码子(AUG)暴露于发夹结构之外,此外将p ET11b核糖体结合位点由GAAGGAGA突变为GAAGAA,以利于翻译复合体的组装以及翻译起始。通过基因克隆的方法将5'端TIR区优化后的序列与s TNFαRI序列一起克隆到p ET11b载体中,并转化大肠杆菌BL21(DE3),阳性转化子经IPTG诱导表达,SDS-PAGE和Western blot检测。结果:通过对PET11b-s TNFαRI 5'TIR mRNA二级结构优化,经SDS-PAGE和Western blot分析表明重组s TNFαRI的表达水平较优化前提高50%~60%。结论:通过对重组载体翻译起始区(TIR)mRNA序列的二级结构优化可以有效提高目的蛋白的表达水平,对进一步工业化生产具有重要的应用价值。  相似文献   

3.
降低mRNA翻译起始区的稳定性原核非融合表达HAb18GEF   总被引:1,自引:1,他引:0  
为在大肠杆菌中非融合表达肝癌相关抗原HAb18G胞外区片段(HAb18GEF),将HAb18GEF基因的cDNA插入原核表达载体pET21a+。通过计算机辅助设计,对重组的HAb18GEF/pET21a+的mRNA翻译起始区(TIR)的二级结构和密码子偏性同时进行预测。结果发现其存在稳定的茎环结构和许多稀有密码子。通过优化二级结构和优化密码子偏性二种策略分别来降低HAb18GEF/pET21a+的mRNA翻译起始区(TIR)的稳定性。在不改变氨基酸序列的前提下,利用密码子的简并性,通过非连续定点突变实现这两种优化。将突变前后的重组子经酶切鉴定和测序验证后,转化感受态JM109DE3宿主菌后,随机挑菌37℃下用IPTG诱导表达。SDSPAGE、间接ELISA、Western blot 和细胞分级分离法分析这些重组子的诱导表达情况。RNA dot blot对比分析优化前后目的基因mRNA的量。结果证明,成功地构建了HAb18GEF/pET21a+及其二种优化突变体。仅优化TIR区二级结构或仅优化TIR区密码子偏性均能实现HAb18GEF蛋白的非融合表达,而未优化的重组子不表达任何HAb18GEF。非融合表达产物在大肠杆菌中主要以包涵体形式存在,高达293%。由于过表达和细胞渗漏,培养基和周质腔中也可检测到少许的HAb18GEF。优化二级结构和优化密码子偏性二种策略的HAb18GEF的非融合表达量基本相同。优化前后HAb18GEF转录的mRNA量没有差别。这些结果表明,降低mRNA翻译起始区的稳定性可实现肝癌相关抗原HAb18G胞外区片段在大肠杆菌中的非融合表达。  相似文献   

4.
通过截短玉米黑粉菌CYP51(P450-14DM,UmCYP51)基因(去除编码跨膜区部分)和选取不同的表达载体,构建了9种重组表达质粒,在大肠杆菌中进行UmCYP51基因的表达,发现只有BL21(DE3)/pET32-Um-35重组表达工程菌获得了表达.对稀有密码子和mRNA翻译起始区二级结构进行分析,结果表明稀有密码子和mRNA翻译起始区二级结构对UmCYP51蛋白的表达都有影响.适用于稀有密码子表达的菌株Rosetta(DE3)不利于UmCYP51蛋白的表达;同时只有翻译起始区二级结构自由能值最低的重组载体pET32-Um-35可以表达.为了设计以UmCYP51为靶标的新型抗真菌抑制剂,基于最新解析的真核生物人类的CYP51晶体结构,利用同源模建的方法构建了UmCYP51的三维结构并进行了分子动力学模拟优化.通过与商品化杀菌剂戊唑醇进行分子对接获得了此类抑制剂与UmCYP51的理论结合方式,阐述了戊唑醇分子的杀菌机理,为开发新型的抗真菌抑制剂奠定了基础.  相似文献   

5.
Mx基因稀有密码子和mRNA结构及大肠杆菌表达 优化   总被引:12,自引:0,他引:12  
通过对稀有密码子和mRNA翻译起始区二级结构的分析, 构建了4种重组表达菌株BL21(DE3)/pET-Mx, Rosseta(DE3)/pET-Mx, BL21(DE3)/pGEX-Mx和Rosseta(DE3)/pGEX-Mx, 在大肠杆菌中进行Mx基因的表达, Rosseta(DE3)/pET-Mx和Rosseta(DE3)/pGEX-Mx重组表达菌中都获得了表达, Western blotting检测到了特异的75 kDa表达产物。实验结果证明稀有密码子和mRNA翻译起始区二级结构对Mx 蛋白表达都有影响, 选择适用于稀有密码子表达的菌株Rosetta(DE3)有利于Mx蛋白的表达, 同时翻译起始区二级结构能值较低的表达载体pGEX-Mx获得的表达量明显增高。实验中首次获得了重组表达鸡全长Mx蛋白的大肠杆菌重组菌。  相似文献   

6.
目的:优化人乳头瘤病毒16型主要衣壳蛋白L1(human papillomavirus type 16 major capsid protein L1,HPV16L1)在毕赤酵母中的表达,并考察可能的影响因素。方法:四个不同序列特征的HPV16L1基因M16、Y16、P16、W16(其中,M16和Y16按酵母密码子优化,P16为哺乳动物细胞密码子优化,而W16为野生型序列)分别克隆于毕赤酵母表达质粒p PinkTM-HC(高基因拷贝菌落筛选)和p PinkTM-LC(低基因拷贝菌落筛选),并转化不同蛋白酶缺陷的宿主菌。甲醇诱导24小时后,取菌体样品经Western blot分析L1蛋白的表达。结果:M16显示了最高的表达水平,其次是Y16与P16,而W16几乎无表达。基因序列密码子应用特征分析显示,4个基因的密码子适应指数从高到低依次为Y16、M16、W16和P16。通过自由能和GC含量分析4个序列的mRNA二级结构,Y16为-409.40 kcal/mol和43.85%;M16为-451.50 kcal/mol和47.83%;P 16为-606.50kcal/mol and 64.10%;W16为-384.70 kcal/mol and 38.01%。蛋白酶缺陷菌株L1表达高于野生型菌株,质粒p PinkTM-HC与p PinkTM-LC介导的表达无明显区别。结论:密码子优化操作显著改善了HPV16L1在毕赤酵母中的表达,但表达水平与密码子利用优劣并不完全对应,提示密码子优化仅是部分原因,而mRNA结构与稳定性变化值得探讨。蛋白酶缺陷菌株提高了HPV16L1蛋白的稳定性,显著影响了表达水平。研究证明基因剂量对HPV16L1的表达未产生明显影响。  相似文献   

7.
响应面分析法优化(R)-扁桃酸发酵培养基   总被引:6,自引:0,他引:6  
采用响应面分析法对Bacillussp.HB20菌株合成(R)-扁桃酸的培养基成分进行优化。首先利用Plackett-Burman试验设计筛选出影响(R)-扁桃酸产率的三个主要因素:麦芽糖、蛋白胨和牛肉膏。在此基础上用最陡爬坡路径逼近最大响应区域,再利用Box-Behnken试验设计及响应面分析法进行回归分析。结果表明,麦芽糖、蛋白胨和牛肉膏浓度与(R)-扁桃酸产率存在显著的相关性,通过求解回归方程得到最佳质量浓度:蛋白胨11.507g/L,牛肉膏6.708g/L,麦芽糖10.907g/L,(R)-扁桃酸产率理论最大值达到66.87%。经模型验证,预测值与验证试验平均值接近,在优化条件下(R)-扁桃酸产率提高了25.87%。  相似文献   

8.
2-氧代-4-苯基丁酸乙酯还原酶产生菌筛选及产酶条件   总被引:1,自引:0,他引:1  
研究了利用生物催化不对称还原的方法制备(R)-2-羟基-4-苯基丁酸乙酯[(R)-HPBE]。以2-氧代-4-苯基丁酸乙酯(OPBE)为底物,通过对实验室保藏菌株进行筛选,得到一株产物立体选择性较高的菌株G2ndida krusei SW2026,并对其发酵产酶条件进行研究。其最适的发酵培养基组成为4.5%葡萄糖,3%蛋白胨,1.5%牛肉膏,0.05%Mn~(2+);适宜的产酶发酵条件为初始pH 6.0,温度28℃,摇床转速180 r/min,发酵周期48 h。将此条件下发酵培养的菌体用于OPBE的不对称还原反应,产物(R)-HPBE的对映体过量值(e.e.)可达97.33%,产率最高达到72.54%。  相似文献   

9.
为研究mRNA翻译起始区结构与基因表达的关系,利用密码子的简并性,在不改变表达产物氨基酸序列的前提下定点突变α8干扰素及αA干扰素衍生物基因的5′端若干位点,使其与表达载体重组后转录形成的mRNA翻译起始区结构发生改变。SDS-PAGE及活性测定证实这些改变提高了外源基因的表达水平。RNA斑点印迹表明突变前后基因转录水平差别不大,表达水平的提高主要由于翻译效率的提高。mRNA翻译起始区二级结构预测提示其生成自由能(ΔG)的变化可能与表达水平的提高有关。  相似文献   

10.
纤维素水解成为葡萄糖需要一系列纤维素酶的作用,其中β-葡萄糖苷酶(β-glucosidases)起着至关重要的作用。来自于培菌白蚁中肠的β-葡萄糖苷酶(MbmgBG1)具有较高的葡萄糖耐受性(1.5 mol/L的葡萄糖,保持60%以上的酶活力),但是,酶活力低和热稳定性差限制了β-葡萄糖苷酶(MbmgBG1)在食品以及工业领域中的应用。因此通过对保守氨基酸附近的非保守氨基酸定点突变,获得点突变体(F167L、T176C、E347I、R354K、N393G和V425M),其中突变体F167L、R354K的比活力(底物pNPG)比MbmgBG1分别高出约2倍和4倍。突变体的K_(cat)/K_m值比野生型大,反映了突变体对底物的亲和力以及催化能力比MbmgBG1强。当酶活力保留60%以上时,MbmgBG1所耐受的葡萄糖浓度为1.5 mol/L,而F167L为2.0 mol/L,R354K为3.0 mol/L。这些特性的增强表明,对活性中心附近保守区域内的非保守氨基酸突变,可以较大程度地影响活性,因此需要更深入地研究β-葡萄糖苷酶的活性中心位点,进行改造以提高催化效率。  相似文献   

11.
The present study was designed to appraise the photoprotective, antioxidant, and antibacterial bioactivities of Ruellia tuberosa leaves extracts (RtPE, RtChl, RtEA, RtAc, RtMe, and RtHMe). The results showed that, RtHMe extracts of R. tuberosa was rich in total phenolic content, i. e., 1.60 mgGAE/g dry extract, while highest total flavonoid content was found in RtAc extract, i. e., 0.40 mgQE/g. RtMe showed effective antioxidant activity (%RSA: 58.16) at the concentration of 120 μL. RtMe, RtEA and RtHMe exhibited effective in vitro antibacterial activity against Gram-negative bacteria (E. coli). In silico docking studies revealed that paucifloside (−11.743 kcal/mol), indole-3-carboxaldehyde (−7.519 kcal/mol), nuomioside (−7.275 kcal/mol), isocassifolioside (−6.992 kcal/mol) showed best docking score against PDB ID 2EX8 [penicillin binding protein 4 (dacB) from Escherichia coli, complexed with penicillin-G], PDB ID 6CQA (E. coli dihydrofolate reductase protein complexed with inhibitor AMPQD), PDB ID 2Y2I [Penicillin-binding protein 1B in complex with an alkyl boronate (ZA3)] and PDB ID 2OLV (from S. aureus), respectively. Docked phytochemicals also showed good drug likeness properties.  相似文献   

12.
13.
The peripheral subunit-binding domain (PSBD) of the dihydrolipoyl acetyltransferase (E2, EC 2.3.1.12) binds tightly but mutually exclusively to dihydrolipoyl dehydrogenase (E3, EC 1.8.1.4) and pyruvate decarboxylase (E1, EC 1.2.4.1) in the pyruvate dehydrogenase multienzyme complex of Bacillus stearothermophilus. Isothermal titration calorimetry (ITC) experiments demonstrated that the enthalpies of binding (DeltaH degrees ) of both E3 and E1 with the PSBD varied with salt concentration, temperature, pH, and buffer composition. There is little significant difference in the free energies of binding (DeltaG degrees = -12.6 kcal/mol for E3 and = -12.9 kcal/mol for E1 at pH 7.4 and 25 degrees C). However, the association with E3 was characterized by a small, unfavorable enthalpy change (DeltaH degrees = +2.2 kcal/mol) and a large, positive entropy change (TDeltaS degrees = +14.8 kcal/mol), whereas that with E1 was accompanied by a favorable enthalpy change (DeltaH degrees = -8.4 kcal/mol) and a less positive entropy change (TDeltaS degrees = +4.5 kcal/mol). Values of DeltaC(p) of -316 cal/molK and -470 cal/molK were obtained for the binding of E3 and E1, respectively. The value for E3 was not compatible with the DeltaC(p) calculated from the nonpolar surface area buried in the crystal structure of the E3-PSBD complex. In this instance, a large negative DeltaC(p) is not indicative of a classical hydrophobic interaction. In differential scanning calorimetry experiments, the midpoint melting temperature (T(m)) of E3 increased from 91 degrees C to 97.1 degrees C when it was bound to PSBD, and that of E1 increased from 65.2 degrees C to 70.0 degrees C. These high T(m) values eliminate unfolding as a major source of the anomalous DeltaC(p) effects at the temperatures (10-37 degrees C) used for the ITC experiments.  相似文献   

14.
Linda Yu  Chang-an Yu 《BBA》1980,593(1):24-38
Purified ubiquinone-binding protein in succinate-ubiquinone reductase (QPs) reconstitutes with pure soluble succinate dehydrogenase to form succinate-ubiquinone oxidoreductase upon mixing of the two proteins in phosphate buffer at neutral pH. The maximal reconstitution was found with a weight ratio of succinate dehydrogenase to QPs of about 5, which is fairly close to the calculated value of 6.5, a value obtained by assuming one mole of QPs reacts with one mole of succinate dehydrogenase. Succinate-cytochrome c reductase was reconstituted when succinate dehydrogenase and QPs were added to Complex III or cytochrome b-c1 III complex (a highly purified ubiquinol-cytochrome c reductase). The reconstituted enzyme possessed kinetic parameters which were identical to those of the native enzyme complex. Interaction between QPs and succinate dehydrogenase resulted in the disappearance of low Km ferricyanide reductase activity from the latter. Unlike soluble succinate dehydrogenase, the reconstituted enzyme, as well as native succinate-cytochrome c reductase, reduced low concentration ferricyanide only in the presence of excess ubiquinone. The apparent Km for ubiquinone was 6 μM for reduction of ferricyanide (300 μM) by succinate, which is similar to the Km when ubiquinone was used as electron acceptor. When 2,6-dichlorophenolindophenol was used as electron acceptor for reconstitution of succinate-ubiquinone reductase very little or no exogeneous ubiquinone was needed to show the maximal activity with QPs made by Method II, indicating that the bound ubiquinone in QPs is enough for enzymatic activity. In addition to restoring the succinate-ubiquinone reductase activity the interaction between QPs and succinate dehydrogenase not only stabilized succinate dehydrogenase but also partially deaggregated QPs. The reconstituted succinate-ubiquinone reductase had a minimal molecular weight of 120000 when the reconstituted system was dispersed in 0.2% Triton X-100. The maximal reconstitution was observed at neutral pH in phosphate buffer, Tris-acetate or Tris-phosphate buffer. Tris-HCl buffer, however, produced a less efficient reconstitution. These results indicate that the interaction between QPs and succinate dehydrogenase may involve some cationic group which has a high affinity for Cl?. Primary amino groups of QPs are not directly involved in the interaction as the reconstitution showed no significant difference when the amino groups of QPs were alkylated with fluorescamine. The Arrhenius plots of reconstituted succinate-ubiquinone reductase show that the enzyme catalyzes the reaction with an activation energy of 19.7 kcal/mol and 26.6 kcal/mol at temperatures above and below 26°C, respectively. These activation energies are similar to those obtained with native enzyme. The Arrhenius plots of the interaction between QPs and succinate dehydrogenase also have a break point at 26°C. The activation energy for this interaction was calculated to be 11.2 kcal/mol and 6.9 kcal/mol for the temperatures above and below the break-point. The significance of the difference in activation energies between the enzymatic reaction and the reconstitution reaction are further explored in the discussion.  相似文献   

15.
Riboswitches are functional mRNA that control gene expression. Thiamine pyrophosphate (TPP) binds to thi-box riboswitch RNA and allosterically inhibits genes that code for proteins involved in the biosynthesis and transport of thiamine. Thiamine binding to the pyrimidine sensor helix and pyrophosphate binding to the pyrophosphate sensor helix cause changes in RNA conformation that regulate gene expression. Here we examine the thermodynamic properties of the internal loop of the pyrophosphate binding domain by comparing the wild-type construct (RNA WT) with six modified 2 × 2 bulged RNA and one 2 × 2 bulged DNA. The wild-type construct retains five conserved bases of the pyrophosphate sensor domain, two of which are in the 2 × 2 bulge (C65 and G66). The RNA WT construct was among the most stable (ΔG°37 = −7.7 kcal/mol) in 1 M KCl at pH 7.5. Breaking the A•G mismatch of the bulge decreases the stability of the construct ∼0.5–1 kcal/mol, but does not affect magnesium binding to the RNA WT. Guanine at position 48 is important for RNA–Mg2+ interactions of the TPP-binding riboswitch at pH 7.5. In the presence of 9.5 mM magnesium at pH 5.5, the bulged RNA constructs gained an average of 1.1 kcal/mol relative to 1 M salt. Formation of a single A+•C mismatch base pair contributes about 0.5 kcal/mol at pH 5.5, whereas two tandem A+•C mismatch base pairs together contribute about 2 kcal/mol.  相似文献   

16.
为检测血管紧张素Ⅱ(angiotensin Ⅱ,AⅡ)对小鼠胚胎干细胞(embryonic stem cells,ESCs)向心肌细胞方向分化的作用,采用10-4 mol/L维生素C诱导小鼠R1胚胎干细胞分化为心肌细胞. Western印记检测胚胎干细胞诱导分化的心肌细胞中表达血管紧张素Ⅱ1 型受体(angiotensin Ⅱ type 1 receptor,AT1R).诱导分化期间用1 μmol/L AⅡ刺激胚胎干细胞,计数搏动拟胚体的比例;诱导分化第14 d用real-time RT-PCR 和Western 印记检测心肌标志物的表达确定其作用. 结果显示,与对照组相比,1 μmol/L AⅡ处理组可显著增加搏动拟胚体的比例,上调心肌标志物mRNA的表达. 预先用1 μmol/L洛沙坦处理1 h后可显著阻碍这种上调作用. 本实验结果表明,AⅡ通过AT1R可促进小鼠R1胚胎干细胞向心肌细胞分化.  相似文献   

17.
Through the use of CD and DSC, the thermal unfolding of holo serum retinol binding protein containing a single, tightly bound retinol ligand was studied at pH 7.4. The DSC endotherm of the holoprotein ([retinol]/[protein] = 1) was asymmetric about the transition temperature of 78 degrees C. Using changes in ellipticity at 230 nm, the thermal unfolding curve was also asymmetric about the inflection point centered near 78 degrees C. van't Hoff enthalpies were determined by three means and compared to the calorimetric enthalpy (delta Hcal) of 200 kcal/mol. A van't Hoff enthalpy of 190 kcal/mol was determined from the dependence of transition temperature on the concentration of the ligand-bound protein. This value agreed well with the van't Hoff enthalpies found from fits of the DSC (delta HvH = 184 kcal/mol) and spectroscopic (delta HvH = 181 kcal/mol) curves to a two-state thermodynamic model that included ligand dissociation (NR in equilibrium with U+R, where NR is the native holoprotein, U is the unfolded apoprotein, and R is retinol). Poor agreement was obtained with a two-state model that ignored ligand dissociation (N in equilibrium with U). Furthermore, the NR in equilibrium with U+R model accounted for the asymmetry in both CD and DSC transitions and yielded a much improved fit of the data over the N in equilibrium with U model. From these considerations and simulations on other equilibrium models, it is suggested that the NR in equilibrium with U+R model is the simplest model that describes the thermal unfolding of this ligand-bound protein.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

18.
The Fe-CO bond dissociation energy (BDE) in myoglobin (Mb) has been calculated with B3LYP quantum mechanics/molecular mechanics methods for 22 different Mb conformations, generated from molecular dynamics simulations. Our average BDE of 8.1 kcal/mol agrees well with experiment and shows that Mb weakens the Fe-CO bond by 5.8 kcal/mol; the calculations provide detailed atomistic insight into the origin of this effect. BDEs for Mb conformations with the R carbonmonoxy tertiary structure are on average 2.6 kcal/mol larger than those with the T deoxy tertiary structure, suggesting two functionally distinct allosteric states. This allostery is partly explained by the reduction in distal cavity steric crowding as Mb moves from its T to R tertiary structure.  相似文献   

19.
The lipolytic protein LipU was conserved in mycobacterium sp. including M. tuberculosis (MTB LipU) and M. leprae (MLP LipU). The MTB LipU was identified in extracellular fraction and was reported to be essential for the survival of mycobacterium. Therefore to address the problem of drug resistance in pathogen, LipU was selected as a drug target and the viability of finding out some FDA approved drugs as LipU inhibitors in both the cases was explored. Three-dimensional (3D) model structures of MTB LipU and MLP LipU were generated and stabilized through molecular dynamics (MD). FDA approved drugs were screened against these proteins. The result showed that the top-scoring compounds for MTB LipU were Diosmin, Acarbose and Ouabain with the Glide XP score of ?12.8, ?11.9 and ?11.7 kcal/mol, respectively, whereas for MLP LipU protein, Digoxin (?9.2 kcal/mol), Indinavir (?8.2 kcal/mol) and Travoprost (?8.2 kcal/mol) showed highest affinity. These drugs remained bound in the active site pocket of MTB LipU and MLP LipU structure and interaction grew stronger after dynamics. RMSD, RMSF and Rg were found to be persistent throughout the simulation period. Hydrogen bonds along with large number of hydrophobic interactions stabilized the complex structures. Binding free energies obtained through Prime/MM-GBSA were found in the significant range from ?63.85 kcal/mol to ?34.57 kcal/mol for MTB LipU and ?71.33 kcal/mol to ?23.91 kcal/mol for MLP LipU. The report suggested high probability of these drugs to demolish the LipU activity and could be probable drug candidates to combat TB and leprosy disease.  相似文献   

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