Integration of F1 and the membrane sector of the proton-ATPase of Escherichia coli. Role of subunit "b" (uncF protein)

Membranes derived from the Escherichia coli strain AN1460 which carries the multicopy plasmid pAN45 (unc+) (Downie, J. A., Langman, L., Cox, G. B., Yanofsky, C., and Gibson, (1980) J. Bacteriol. 143, 8-17) were enriched 5- to 10-fold in proton-ATPase activity. Incubation of F1-depleted AN1460 membranes with trypsin abolished F1-binding ability but did not inhibit proton transport through the membrane sector (F0). Sodium dodecyl sulfate-gel electrophoresis indicated that subunit "b" (uncF protein) of F0 was cleaved by trypsin and prebound F1 protected against the trypsin effect. Subunits "a" (uncB protein) and "c" (uncE protein) were unaffected by the trypsin treatment. A water-soluble fragment (Mr = 14,800) was liberated after trypsin treatment and appeared to arise from subunit b. Studies of enzyme hybridization and of F1 binding to membranes derived from strains containing mutations in uncB, F, and E genes supported the suggestion that subunit b is involved in F1 binding to the F0. Also, extraction of membranes with KSCN increased the relative proportion of subunit b in the membrane and this coincided with a parallel increase in trypsin-sensitive F1-binding ability. It is proposed that subunit b is involved in binding of F1 to the F0; this agrees with the presumed role of the protein as deduced from predictions of its secondary and tertiary structure (Walker, J. E., Saraste, M., and Gay, N. J. (1982) Nature (Lond.) 298, 867-869; Senior, A. E. (1983) Biochim. Biophys. Acta, in press).     

Cathepsin B Is Secreted Apically from Xenopus 2F3 Cells and Cleaves the Epithelial Sodium Channel (ENaC) to Increase Its Activity

The epithelial sodium channel (ENaC) plays an important role in regulating sodium balance, extracellular volume, and blood pressure. Evidence suggests the α and γ subunits of ENaC are cleaved during assembly before they are inserted into the apical membranes of epithelial cells, and maximal activity of ENaC depends on cleavage of the extracellular loops of α and γ subunits. Here, we report that Xenopus 2F3 cells apically express the cysteine protease cathepsin B, as indicated by two-dimensional gel electrophoresis and mass spectrometry analysis. Recombinant GST ENaC α, β, and γ subunit fusion proteins were expressed in Escherichia coli and then purified and recovered from bacterial inclusion bodies. In vitro cleavage studies revealed the full-length ENaC α subunit fusion protein was cleaved by active cathepsin B but not the full-length β or γ subunit fusion proteins. Both single channel patch clamp studies and short circuit current experiments show ENaC activity decreases with the application of a cathepsin B inhibitor directly onto the apical side of 2F3 cells. We suggest a role for the proteolytic cleavage of ENaC by cathepsin B, and we suggest two possible mechanisms by which cathepsin B could regulate ENaC. Cathepsin B may cleave ENaC extracellularly after being secreted or intracellularly, while ENaC is present in the Golgi or in recycling endosomes.     

Immunoelectron microscopic localization of the F1F0 ATPase (ATP synthase) on the cytoplasmic membrane of alkalophilic Bacillus firmus RAB

Evidence that the F1F0 ATPase (ATP synthase) of alkalophilic Bacillus firmus RAB is localized exclusively on the cytoplasmic membrane was obtained by immunogold electron microscopy using a highly specific polyclonal antibody against the beta subunit of Escherichia coli F1F0 ATPase. The energetic problem faced by cells of B. firmus RAB growing oxidatively at pH 10.5 despite a low protonmotive force across the cytoplasmic membrane cannot, therefore, be circumvented by localization of energy transducing functions on hypothetical internal membranes.     

重组人IL-17A和IL-17F的制备方法及活性测定

人IL-17A和IL-17F具有很高的同源性,在炎症性疾病、自身免疫性疾病和肿瘤中都发挥着重要的作用,是当前研究的热点.应用原核表达系统在大肠杆菌BL21(DE3)中高效表达了人IL-17A和IL-17F;经培养条件的优化,未发现可溶性目的蛋白的表达,免疫印记分析显示,重组蛋白位于包涵体中;对包涵体进行洗涤、凝胶过滤层析纯化和柱上复性,获得重折叠的可溶性蛋白;随后用SDS-PAGE对蛋白样品进行了纯度分析、采用免疫印记和质谱的方法鉴定蛋白产物成分、用ME3T3-E1和RAW264.7两个细胞株对IL-17A、IL-17F的生物学活性进行测定.结果显示,柱上复性的方法制备的谊重组蛋白具有较高的纯度和活性.建立的重组人IL-17A和IL-17F的制备方法可为相关研究中细胞因子的大量应用提供参考.     

Functional effects and cross-reactivity of antibody to purified subunit b (uncF protein) of Escherichia coli proton-ATPase

Subunit b (uncF protein) of the proton-ATPase (F1F0) of Escherichia coli was purified from membranes of strain AN1460 (unc+). Antibody to purified subunit b was raised in rabbits. It reacted with F1-depleted membranes and blocked F1 binding. Bound antibody had no effect on proton transport through F0. F1-Depleted membranes competed with purified subunit b for antibody in an enzyme-linked immunosorbent assay. F1-Depleted membranes which had been pretreated with trypsin or preincubated with saturating amounts of soluble F1 competed poorly with purified subunit b for antibody. The antibody to subunit b was used to further evaluate the trypsin-cleavage data previously reported [D. S. Perlin, D. N. Cox, and A. E. Senior (1983) J. Biol. Chem. 258, 9793-9800]. The results indicated that trypsin proteolysis of F1-depleted membranes resulted in the transient appearance of three fragments of subunit b (Mr = 16,400, 15,700, and 15,500) that remained tightly bound to the membrane. A water-soluble fragment (Mr 14,800), previously thought to be derived from subunit b, was not detected by the antibody. The antibody to subunit b did not cross-react with any subunit of mitochondrial, chloroplast, or other bacterial proton-ATPase, or with the proton-ATPase of clathrin-coated vesicles, plant microsomal membranes, or Neurospora crassa plasma membranes.     

Expression in Escherichia coli of c-type cytochrome genes from Rhodopseudomonas viridis.

The genes coding for the photosynthetic reaction center cytochrome c subunit (pufC) and the soluble cytochrome c2 (cycA) from the purple non-sulfur bacterium Rhodopseudomonas viridis were expressed in Escherichia coli. Biosynthesis of the reaction center cytochrome without a signal peptide resulted in the formation of inclusion bodies in the cytoplasm amounting to 14% of the total cellular protein. A series of plasmids coding for the cytochrome subunit with varying N-terminal signal peptides was constructed in attempts to achieve translocation across the E. coli cytoplasmic membrane and heme attachment. However, the two major recombinant proteins with N-termini corresponding to the signal peptide and the cytochrome were synthesized in E. coli as non-specific aggregates without heme incorporation. An increased ratio of precursor as compared to 'processed' apo-cytochrome was obtained when expression was carried out in a proteinase-deficient strain. Cytochrome c2 from R. viridis was synthesized in E. coli as a precursor associated with the cytoplasmic membrane. An expression plasmid was designed encoding the N-terminal part of the 33 kDa precursor protein of the oxygen-evolving complex of Photosystem II from spinach followed by cytochrome c2. Two recombinant proteins without heme were found to aggregate as inclusion bodies with N-termini corresponding to the signal peptide and the mature 33 kDa protein.     

Green fluorescent protein as an indicator to monitor membrane protein overexpression in Escherichia coli.

Escherichia coli is one of the most widely used vehicles to overexpress membrane proteins (MPs). Currently, it is not possible to predict if an overexpressed MP will end up in the cytoplasmic membrane or in inclusion bodies. Overexpression of MPs in the cytoplasmic membrane is strongly favoured to overexpression in inclusion bodies, since it is relatively easy to isolate MPs from membranes and usually impossible to isolate them from inclusion bodies. Here we show that green fluorescent protein (GFP), when fused to an overexpressed MP, can be used as an indicator to monitor membrane insertion versus inclusion body formation of overexpressed MPs in E. coli. Furthermore, we show that an overexpressed MP can be recovered from a MP-GFP fusion using a site specific protease. This makes GFP an excellent tool for large-scale MP target selection in structural genomics projects.     

Lengthening the second stalk of F(1)F(0) ATP synthase in Escherichia coli

In Escherichia coli F(1)F(0) ATP synthase, the two b subunits dimerize forming the peripheral second stalk linking the membrane F(0) sector to F(1). Previously, we have demonstrated that the enzyme could accommodate relatively large deletions in the b subunits while retaining function (Sorgen, P. L., Caviston, T. L., Perry, R. C., and Cain, B. D. (1998) J. Biol. Chem. 273, 27873-27878). The manipulations of b subunit length have been extended by construction of insertion mutations into the uncF(b) gene adding amino acids to the second stalk. Mutants with insertions of seven amino acids were essentially identical to wild type strains, and mutants with insertions of up to 14 amino acids retained biologically significant levels of activity. Membranes prepared from these strains had readily detectable levels of F(1)F(0)-ATPase activity and proton pumping activity. However, the larger insertions resulted in decreasing levels of activity, and immunoblot analysis indicated that these reductions in activity correlated with reduced levels of b subunit in the membranes. Addition of 18 amino acids was sufficient to result in the loss of F(1)F(0) ATP synthase function. Assuming the predicted alpha-helical structure for this area of the b subunit, the 14-amino acid insertion would result in the addition of enough material to lengthen the b subunit by as much as 20 A. The results of both insertion and deletion experiments support a model in which the second stalk is a flexible feature of the enzyme rather than a rigid rod-like structure.     

Optimization of the primary recovery of human interferon alpha2b from Escherichia coli inclusion bodies

The human interferon alpha2b (hu-IFNalpha2b) gene was cloned in Escherichia coli JM109(DE3) and the recombinant protein was expressed as cytoplasmic inclusion bodies (IB). The present work discusses the recovery of hu-IFNalpha2b IB from the E. coli cells. An optimized protocol is proposed based on the sequential evaluation of recovery steps and parameters: (i) cell disruption, (ii) IB recovery and separation from cell debris, (iii) IB washing, and (iv) IB solubilization. Parameters such as hu-IFNalpha2b purity and recovery yield were measured after each step. The optimized recovery protocol yielded 60% of hu-IFNalpha2b with a purity of up to 80%. The protein was renatured at high concentration after recovery and it was found to display biological activity.     

Mutations in the conserved proline 43 residue of the uncE protein (subunit c) of Escherichia coli F1F0-ATPase alter the coupling of F1 to F0

The conserved Pro43 residue of the uncE protein (subunit c) of the Escherichia coli F1F0-ATPase was changed to Ser or Ala by oligonucleotide-directed mutagenesis, and the mutations were incorporated into the chromosome. The resultant mutant strains were capable of oxidative phosphorylation as indicated by their ability to grow on succinate and had growth yields on glucose that were 80-90% of wild type. Membrane vesicles from the mutants were slightly less efficient than wild type vesicles in ATP-driven proton pumping as indicated by ATP-dependent quenching of quinacrine fluorescence. The decreased quenching response was not due to increased H+ leakiness of the mutant membranes or to loss of F1-ATPase activity from the membrane. These results indicate that the mutant F1F0-ATPases are defective in coupling ATP hydrolysis to H+ translocation. The membrane ATPase activity of the mutants was inhibited less by dicyclohexylcarbodiimide than that of wild type. The decrease in sensitivity to inhibition by dicyclohexylcarbodiimide was caused primarily by dissociation of the F1-ATPase from the mutant F0 in the ATPase assay mixture. These results support the idea that Pro43, and neighboring conserved polar residues play an important role in the binding and functional coupling of F1 to F0. Although a Pro residue is found at position 43 in all species of subunit c studied, surprisingly, it is not absolutely essential to function.     

Expression and single-step purification of mercury transporter (merT) from <Emphasis Type="Italic">Cupriavidus metallidurans</Emphasis> in <Emphasis Type="Italic">E. coli</Emphasis>

The mercury transporter, merT, from Cupriavidus metallidurans was cloned into pRSET-C and expressed in various E. coli hosts. Expression of merT gene failed in common expression hosts like E. coli BL21(DE3), E. coli BL21(DE3)pLysS and E. coli GJ1158 due to expression induced toxicity. The protein was successfully expressed in E. coli C43(DE3) as inclusion bodies. The inclusion bodies were solubilized with Triton X-100 detergent. The detergent solubilized protein with N-terminal His-tag was purified in a single-step by immobilized metal affinity chromatography with a yield of 8 mg l⁻¹.     

Overexpression and Purification of the Escherichia coli Inner Membrane Enzyme Acyl–Acyl Carrier Protein Synthase in an Active Form

Acyl–acyl carrier protein synthase (Aas) is widely used to synthesize thioester adducts of fatty acids between 8 and 18 carbons in length enzymatically to the phosphopantetheine group of acyl carrier protein. The enzyme is an 80.6-kDa inner membrane protein that functions in vivo as a 2-acylglycerophosphoethanolamine acyltransferase. The E. coli aas open reading frame was inserted into the expression plasmid pET28a so that, upon expression, a 21-amino-acid extension containing 6 consecutive histidine residues was added to the carboxyl terminus. The plasmid was designated pAasH. The activity of Aas in membranes was assessed from several cell lines. Membranes from the commonly used host line BL21(DE3) containing pAasH accumulated 30-fold and 38-fold more Aas activity than membranes from BL21(DE3) cells lacking the plasmid, when induced with isopropyl β- -thiogalactopyranoside (IPTG) or lactose, respectively. When pAasH was expressed under IPTG induction in cell line C41(DE3), a previously described cell line selected to enhance the expression of membrane proteins, Aas levels accumulated to 135-fold higher levels than in the cell line lacking the plasmid. Functional Aas can be isolated from either BL21(DE3) or C41(DE3) cell lines by differential centrifugation, followed by detergent extraction with Triton X-100 and nickel nitrilotriacetic acid affinity chromatography. The overexpression of Aas in cell line C41(DE3) is noteworthy compared to cell line BL21(DE3) because it results in a 3- to 4-fold higher accumulation of active enzyme in the membrane fraction and a lower proportion of inactive protein in the inclusion body.     

一种新型融合蛋白(RGD)3/tTF的基因表达与活性分析

为了发展一种新型的融合蛋白(RGD)3/tTF用于肿瘤血管的选择性栓塞治疗,利用PCR技术重组(RGD)3/tTF融合基因,克隆于pET22b( )载体,表达于E.coliBL21(DE3)。用镍柱纯化融合蛋白。凝血实验与FⅩ活化实验检测融合蛋白tTF组分的活性。间接ELISA分析(RGD)3/tTF与αvβ3的特异结合能力。pET22b( )/(RGD)3/tTF重组质粒成功获得并表达于E.coliBL21(DE3)。纯化蛋白(RGD)3/tTF能有效诱发血液凝固,活化FⅩ。(RGD)3/tTF与αvβ3的特异结合能力比RGD/tTF提高了32%。新型融合蛋白(RGD)3/tTF已在E.coli系统成功表达,表达蛋白保持tTF的活性并显示比RGD/tTF更高的与αvβ3的结合能力。     

重组人脑源性神经营养因子的纯化和鉴定

在确定培养条件和发酵参数后 ,工程菌 E.coli BL2 1 ( DE3) /PVBN6在 5 L发酵罐中稳定表达。获得的菌体经超声破碎 ,离心收集包含体。 6mol/L盐酸胍缓冲液溶解包含体 ,用透析法将盐酸胍替换成脲后 ,经过 CM Sepharose F.F.阳离子交换色谱和 C8反相色谱 ,可得到纯度达 95 %以上的rh BDNF。Western- blot表明 ,rh BDNF与抗 - h BDNF多克隆抗体有结合特异性。用 9日龄鸡胚背根神经节测定生物活性 ,rh BDNF活性为 5 0 ng/ml。N-末端氨基酸序列测定表明 rh BDNF N-末端为Met,其后 1 6个氨基酸残基与天然 h BDNF N-末端氨基酸残基序列一致     

Novel method for expression and purification of human pigment epithelium-derived factor with biological activities in Escherichia coli

We developed a novel method for the expression and purification of recombinant human PEDF in Escherchia coli, and proved it to be simple, convenient, and cheap to obtain this protein with biological activity intact. Human PEDF gene, amplified by PCR from human retinal cNDA library, was cloned into the prokaryotic expression vector pET-22b(+). The recombinant pET-22b(+)/PEDF was expressed in E. coli strain BL21(DE3). The recombinant protein showed a molecular weight of about 50 kDa and was mainly in the form of inclusion bodies according to SDS-PAGE and Western blot analysis. The insoluble rPEDF was solublized from inclusion bodies by denaturation using 6 M urea, purified by His-tag affinity chromatography, and renatured to natural structure by dialysis in the presence of DTT. The rPEDF could cell-type-specifically inhibit HRCEC proliferation in a dose-dependent manner and induce HRCEC apoptosis.     

植原体免疫主导膜蛋白Imp基因原核表达载体构建及表达

旨在构建植原体免疫主导膜蛋白Imp基因原核表达载体,并进行初步表达。以重组克隆质粒pMD18-T-Imp为模板,PCR扩增Imp基因片段。构建表达载体pET-28a(+)-Imp,转化宿主菌E.coliBL21(DE3)。筛选阳性克隆,提取重组质粒作PCR鉴定、酶切鉴定及IPTG诱导表达鉴定。PCR及双酶切结果显示,重组质粒pET-28a(+)-Imp构建成功。经IPTG诱导BL21(pET-28a(+)-Imp)表达约20 kD的蛋白,与预期的携带6×His-Tag的目的蛋白(19.5 kD)大小相符,主要以包涵体形式存在。结果显示,构建的表达载体pET-28a(+)-Imp在E.coliBL21(DE3)中能够达一定量表达,为进一步纯化Imp蛋白奠定基础。     

The polar domain of the b subunit of Escherichia coli F1F0-ATPase forms an elongated dimer that interacts with the F1 sector.

A soluble form of the b subunit of the F0 sector of the F1F0-ATPase of Escherichia coli has been produced, purified, and characterized. In this form of the protein, designated bsol, residues 25-146 (the carboxyl terminus) of b have been fused to an amino-terminal octapeptide extension derived from the vector pUC8. The inferred subunit molecular weight of bsol is 15,459. bsol protein was expressed in E. coli as a soluble cytoplasmic protein and was readily purified to homogeneity by conventional methods. The molecular weight of bsol, determined by sedimentation equilibrium, was 31,200, indicating that the protein is dimeric. Chemical cross-linking studies supported this conclusion. However, bsol sedimented with a coefficient of just 1.8 S and behaved on size exclusion chromatography with an apparent molecular weight of 80,000-85,000. These results indicate that the protein exists in solution as a highly elongated dimer. The circular dichroism spectrum indicated that bsol is highly alpha-helical. Binding of bsol to F1-ATPase was directly demonstrated by size exclusion chromatography. bsol also inhibited the binding of F1-ATPase to F1-depleted membrane vesicles, as measured by reconstitution of energy-dependent quinacrine fluorescence quenching. This result implies that bsol and F0 compete for binding to the same site on F1. The apparently normal interaction of bsol with F1-ATPase strongly suggests that the recombinant protein assumes the correct structure. No substantial effects of bsol on the ATPase activity of purified F1 were observed.     

H+-ATPase activity of Escherichia coli F1F0 is blocked after reaction of dicyclohexylcarbodiimide with a single proteolipid (subunit c) of the F0 complex

Dicyclohexylcarbodiimide (DCCD) specifically inhibits the F1F0-H+-ATP synthase complex of Escherichia coli by covalently modifying a proteolipid subunit that is embedded in the membrane. Multiple copies of the DCCD-reactive protein, also known as subunit c, are found in the F1F0 complex. In order to determine the minimum stoichiometry of reaction, we have treated E. coli membranes with DCCD, at varying concentrations and for varying times, and correlated inhibition of ATPase activity with the degree of modification of subunit c. Subunit c was purified from the membrane, and the degree of modification was determined by two methods. In the "specific radioactivity" method, the moles of [14C]DCCD per total mole of subunit c was calculated from the radioactivity incorporated per mg of protein, and conversion of mg of protein to mol of protein based upon amino acid analysis. In the "high performance liquid chromatography (HPLC) peak area" method, the DCCD-modified subunit c was separated from unmodified subunit c on an anion exchange AX300 HPLC column, and the areas of the peaks from the chromatogram quantitated. The shape of the modification versus inhibition curve indicated that modification of a single subunit c per F0 was sufficient to abolish ATPase activity. The titration data were fit by nonlinear regression analysis to a single hit mathematical model, A = Un(1 - r) + r, where A is the relative activity, U is the ratio of unmodified/total subunit c, n is the number of subunit c per F0, and r is a residual fraction of ATPase activity that was resistant to inhibition by DCCD. The two methods gave values for n equal to 10 by the specific radioactivity method and 14 by the HPLC peak area method, and values for r of 0.28 and 0.30, respectively. Most of the r value was accounted for by the observed dissociation of 15-20% of the F1-ATPase from the membrane under ATPase assay conditions. When the minimal, experimentally justified value of r = 0.15 was used in the equation above, the calculated values of n were reduced to 8 and 11, respectively. The value of n determined here, with a probable range of uncertainty of 8-14, is consistent with, and provides an independent type of experimental support for, the suggested stoichiometry of 10 +/- 1 subunit c per F1F0, which was determined by a more precise radiolabeling method (Foster, D. L., and Fillingame, R. H. (1982) J. Biol. Chem. 257, 2009-2015).     

Expression, refolding, and characterization of a novel recombinant dual human stem cell factor

A novel recombinant dual human stem cell factor (rdhSCF) gene which consisted of a full-length hSCF(1-165aa) cDNA and a truncated hSCF (1-145aa) cDNA, linked by a peptide (GGGGSGGGGSGG) coding region, was constructed and cloned into Escherichia coli expression vector pET-22b. The rdhSCF was expressed at high level in E. coli BL21(DE3) and existed mainly as inclusion bodies. The inclusion bodies were solubilized in urea and refolded by ion-exchange chromatography. After renaturation, the purity of the yielded rdhSCF was up to 90%. Cell proliferation assay showed that the specific activity of the rdhSCF was 2.86x10(5) U/mg, about 1.66 times as high as that of monomer rhSCF expressed in E. coli.     

鲎血细胞中脂多糖结合蛋白TALF在大肠杆菌中的表达研究

TALF(Tachyleus antilipoposaccharide factor)对细菌内毒素（LPS）的核心部分有抑制作用。研究TALF cDNA基因在大肠杆菌中的表达,首先将TALF cDNA基因分别插入大肠杆菌表达载体pGEX-4T-2、pET22b、pET28a中,构建重组表达质粒,转化于大肠杆菌BL21(DE3)。结果表明克隆于pET22b、pET28a中的TALF cDNA基因没有表达,而融合了GST的TALF基因（GST-TALF）能够在大肠杆菌中表达,并形成包涵体。从1L培养基中可获得4mg纯度为91%的GST-TALF融合蛋白。经复性和纯化后的融合蛋白GST-TALF几乎检测不到抑菌活性及LPS中和活性,但该融合蛋白经凝血酶消化后表现出明显的体外抑菌活性及LPS中和活性。