High-level expression of a proteolytically sensitive diphtheria toxin fragment in Escherichia coli.

ABM508 is a recombinant fusion protein consisting of the N-terminal 485 amino acids of diphtheria toxin joined to alpha-melanocyte-stimulating hormone. When expressed in Escherichia coli under the control of the tox promoter and signal sequence, ABM508 is severely degraded. When overexpressed from a thermoinducible lambda pR promoter fusion, ABM508 is largely insoluble. We compared the expression of ABM508 (501 amino acids) to a full-length mutant form of the toxin (CRM197; 535 amino acids) and found that CRM197 showed minimal proteolysis. Thus, the removal of the C-terminal 50 amino acids of the toxin destabilizes the protein, making it a target for proteases. Proteolysis of ABM508 could be reduced by removal of the tox signal sequence (thereby directing the protein to the cytoplasm) and growth in lon and htpR mutant strains of E. coli. We also showed that the solubility of tox gene products expressed in E. coli was directly related to the growth temperature of the culture. Thus, a fragment A fusion protein (223 amino acids), ABM508, and CRM197 were found in soluble extracts when expressed at 30 degrees C but could not be released by the same procedures after growth at 42 degrees C. On the basis of these observations, we fused the coding sequences for mature ABM508 to the trc promoter (inducible at 30 degrees C by isopropyl-beta-D-thiogalactoside) and expressed this construct in a lon htpR strain of E. coli. This plasmid made 10 mg of soluble tox protein per liter of culture (7.7% of the total cell protein) or 14 times more than our previous maximal level. Extracts from lon htpR cells harboring this plasmid had high levels of ADP-ribosyltransferase activity, and although proteolysis still occurred, the major tox product corresponded to full-length ABM508.     

Construction of a high-copy "ATG vector" for expression in Escherichia coli.

We report the construction of an inducible, high-copy plasmid for the expression of foreign proteins in Escherichia coli. This plasmid, pPB1, combines the trc promoter, beta-galactosidase translation start site, and polylinker of pKK233-2 with the origin of replication region of pUC19. Replacement of the origin of replication of pKK233-2 results in a threefold increase in plasmid copy number of pPB1 compared with pKK233-2. Subclones of the cDNA for rabbit muscle fructose-1,6-bisphosphate aldolase (E.C. 4.1.2.13) in the two expression plasmids exhibit a comparable difference in copy number. An increase in protein expression measured by SDS-PAGE and aldolase specific activities reflects the increased copy number. Specific activities of aldolases in bacterial extracts differ approximately sixfold between the two expression plasmids in E. coli JM83. Aldolase A can compose up to 40% of the total protein in E. coli JM83 when expressed in pPB1, from which more than 100 mg of purified enzyme can be obtained per liter culture.     

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.     

Signal sequence of preproglycinin affects production of the expressed protein in Escherichia coli

The effect of the signal peptide portion on the bacterial production of preproglycinin, a precursor of soybean storage protein, was examined. Nucleotide sequences corresponding to the signal peptide and the mature N-terminal region were deleted stepwise from the cDNA encoding the glycinin A1aB1b subunit precursor, and the deleted cDNAs were placed under the control of trc promoter in an expression vector pKK233-2. When the amounts of the protein products in Escherichia coli from each expression plasmid were determined, no accumulation of preproglycinin was observed from the plasmids with the full length or the five amino acids of the signal sequence. However, significant accumulation of the preproglycinin homologue proteins was noted from the plasmids retaining less than three amino acids of the signal sequence depending on the extent of deletion. N-terminal amino acid sequences of the products coincided with those predicted from the deleted cDNAs. The preproglycinin homologue proteins expressed from the mutant plasmids assembled into trimers of about 8S.     

Domain structure and interaction within the pentafunctional arom polypeptide.

The AROM locus of Aspergillus nidulans specifies a pentafunctional polypeptide catalysing five consecutive steps leading to the production of 5-enolpyruvylshikimate 3-phosphate in the shikimate pathway. Aided by oligonucleotide-mediated site-directed mutagenesis, the whole AROM locus and various overlapping subfragments from within it have been fused to the powerful hybrid trc promoter in the Escherichia coli plasmid pKK233-2. Expression of these subfragments in appropriate aro mutants of E. coli has (a) allowed the delineation of functional domains within the arom polypeptide, (b) shown that the arom polypeptide falls in two independently folding and functioning regions, the N-terminal half specifying 3-dehydroquinate (DHQ) synthase and EPSP synthase and the C-terminus specifying shikimate kinase, biosynthetic 3-dehydroquinase (DHQase) and shikimate dehydrogenase, and (c) strongly suggested an interaction between the DHQ synthase and EPSP synthase domains to stabilise the EPSP synthase activity. In addition an isoenzyme of biosynthetic DHQase, catabolic DHQase, encoded by the QUTE gene of A. nidulans has been transcribed from the trc promoter and upon isopropyl-thio-beta-D-galactoside induction produces up to 20% of the total soluble cell protein.     

Epidermolytic toxin serotype B of Staphylococcus aureus is plasmid-encoded

Abstract The gene coding for epidermolytic toxin serotype B ( etb ) was cloned in a plasmid expression vector in Escherichia coli . Its expression was dependent on the vector plasmid's trc promoter. A polypeptide immunochemically indistinguishable from the purified staphylococcal toxin and with the same molecular weight was predominantly localized in the periplasm of E. coli . The etb gene resides on a 1.7 kb Hin dIII fragment of the 42 kb plasmid pTC142 present in the parental Staphylococcus aureus strain.     

Metabolic engineering of the nonmevalonate isopentenyl diphosphate synthesis pathway in Escherichia coli enhances lycopene production

Isopentenyl diphosphate (IPP) is the common, five-carbon building block in the biosynthesis of all carotenoids. IPP in Escherichia coli is synthesized through the nonmevalonate pathway, which has not been completely elucidated. The first reaction of IPP biosynthesis in E. coli is the formation of 1-deoxy-D-xylulose-5-phosphate (DXP), catalyzed by DXP synthase and encoded by dxs. The second reaction in the pathway is the reduction of DXP to 2-C-methyl-D-erythritol-4-phos- phate, catalyzed by DXP reductoisomerase and encoded by dxr. To determine if one or more of the reactions in the nonmevalonate pathway controlled flux to IPP, dxs and dxr were placed on several expression vectors under the control of three different promoters and transformed into three E. coli strains (DH5alpha, XL1-Blue, and JM101) that had been engineered to produce lycopene. Lycopene production was improved significantly in strains transformed with the dxs expression vectors. When the dxs gene was expressed from the arabinose-inducible araBAD promoter (P(BAD)) on a medium-copy plasmid, lycopene production was twofold higher than when dxs was expressed from the IPTG-inducible trc and lac promoters (P(trc) and P(lac), respectively) on medium-copy and high-copy plasmids. Given the low final densities of cells expressing dxs from IPTG-inducible promoters, the low lycopene production was probably due to the metabolic burden of plasmid maintenance and an excessive drain of central metabolic intermediates. At arabinose concentrations between 0 and 1.33 mM, cells expressing both dxs and dxr from P(BAD) on a medium-copy plasmid produced 1.4-2.0 times more lycopene than cells expressing dxs only. However, at higher arabinose concentrations lycopene production in cells expressing both dxs and dxr was lower than in cells expressing dxs only. A comparison of the three E. coli strains transformed with the arabinose-inducible dxs on a medium-copy plasmid revealed that lycopene production was highest in XL1-Blue.     

Synthesis, cloning, and expression in Escherichia coli of a spinach acyl carrier protein-I gene

A synthetic gene of 268 bp encoding the 82 amino acid spinach acyl carrier protein (ACP)-I was constructed based on the known amino acid sequence. Two gene fragments, one encoding the amino-terminal portion and the other the carboxy-terminal portion of the protein, were assembled from synthetic oligonucleotides and inserted into the phage M13mp19. These partial gene constructions were joined and inserted into the plasmid pTZ19R. DNA sequencing confirmed the accuracy of the constructions. The synthetic gene was then subcloned into the Escherichia coli expression vector pKK233-2, under the control of the trc promoter. Western blot analysis and radioimmunoassay indicated that E. coli cells carrying this plasmid produced up to 6 mg/liter of a protein which was immunologically cross-reactive and similar in electrophoretic mobility to authentic spinach acyl carrier protein. The bacterial cells were able to attach the phosphopantetheine prosthetic group to the synthetic plant gene product allowing it to be acylated in vitro by acyl-ACP synthetase.     

System for the expression of recombinant hemoproteins in Escherichia coli

Expression of recombinant hemoproteins in Escherichia coli is often limited because a vast majority of the protein produced lacks the heme necessary for function. This is compounded by the fact that standard laboratory strains of E. coli have a limited capacity to withdraw heme from the extracellular environment. We are developing a new tool designed to increase the heme content of our proteins of interest by simply supplementing the expression medium with low concentrations of hemin. This hemoprotein expression (HPEX) system is based on plasmids (pHPEX1-pHPEX3) that encode an outermembrane-bound heme receptor (ChuA) from E. coli O157:H7. This heme receptor, and others like it, confers on the host the ability to more effectively internalize exogenous heme. Transformation of a standard laboratory E. coli protein expression strain (BL-21 [DE3]) with the pHPEX plasmid led to the expression of a new protein with the appropriate molecular weight for ChuA. The receptor was functional as demonstrated by the ability of the transformant to grow on iron-deficient media supplemented with hemin, an ability that the unmodified expression strain lacked. Expression of our proteins of interest, catalase-peroxidases, using this system led to a dramatic and parallel increase in heme content and activity. On a per-heme basis, the spectral and kinetic properties of HPEX-derived catalase-peroxidase were the same as those observed for catalase-peroxidases expressed in standard E. coli-based systems. We suggest that the pHPEX plasmids may be a useful addition to other E. coli expression systems and may help address a broad range of problems in hemoprotein structure and function.     

Escherichia coli tryptophan synthase: synthesis of catalytically competent alpha subunit in a cell-free system containing preacylated tRNAs

A cell-free protein biosynthesizing system prepared from Escherichia coli CF300 was found to synthesize E. coli tryptophan synthase alpha subunit in a time-dependent manner when programmed with pBN69 plasmid DNA. This plasmid contains the trp promoter from Serratia marcescens adjacent to the coding region of E. coli tryptophan synthase alpha protein [Nichols, B.P., & Yanofsky, C. (1983) Methods Enzymol. 101, 155-164]. The synthesized tryptophan synthase alpha subunit was found to be indistinguishable from authentic alpha subunit protein when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and to have the same specific activity for catalyzing the conversion of indole----L-tryptophan by tryptophan synthase beta 2 subunit, as well as the conversion of indole + glyceraldehyde 3-phosphate to indole-3-glycerol phosphate. In the absence of exogenously added phenylalanine, admixture of E. coli phenylalanyl-tRNAPhe to the protein biosynthesizing system stimulated the production of functional alpha protein; the analogous result was obtained when valine was replaced by E. coli valyl-tRNAVal. The ability of a misacylated tRNA to participate in alpha protein synthesis in this system was established by the use of E. coli phenylalanyl-tRNAVal in the absence of added valine. Protein biosynthesis proceeded normally and gave a product having the approximate molecular weight of tryptophan synthase alpha subunit; as expected, this polypeptide lacked catalytic activity.     

Cloning of the nptII gene of Escherichia coli and construction of a recombinant strain harboring functional recA and nptII antibiotic resistance

In an attempt to clone the ORF of the nptII gene of Escherichia coli K12 (ATCC 10798), two degenerate primers were designed based on the nptII sequence of its Tn5 transposon. The nptII ORF was placed under the control of the E. coli hybrid trc promoter, in the pKK388-1 vector, transformed into E. coli DH5α ΔrecA (recombinant, deficient strain). Transferred cells were tested for ampicillin, tetracycline, kanamycin, neomycin, geneticin, paromomycin, penicillin, and UV resistance. The neomycin phosphotransferase gene of E. coli was cloned successfully and conferred kanamycin, neomycin, geneticin, and paromomycin resistance to recombinant DH5α; this did not inhibit insertion of additional antibiotic resistance against ampicillin and tetracycline, meaning the trc promoter can express two different genes carried by two different plasmids harbored in the same cell. This resistance conferral process could be considered as an emulation of horizontal gene transfer occurring in nature and would be a useful tool for understanding mechanisms of evolution of multidrug-resistant strains.     

Facilitation of bacteriophage lambda DNA injection by inner membrane proteins of the bacterial phosphoenol-pyruvate: carbohydrate phosphotransferase system (PTS)

Infection of Escherichia coli by bacteriophage lambda depends on two membrane protein complexes: (i) maltoporin (LamB) in the outer membrane for adsorption and (ii) the IIC(Man)-IID(Man) complex of the mannose transporter in the inner membrane for DNA penetration. IIC(Man) and IID(Man) are components of the phosphoenolpyruvate: sugar phosphotransferase system (PTS) which together with the IIAB(Man) subunit mediate transport and phosphorylation of sugars. To identify structural determinants important for penetration of lambda DNA, the homologous IIC-IID complexes of E. coli, K. pneumoniae and B. subtilis, and chimeric complexes between the IIC and IID were characterized. All three complexes support sugar transport in E. coli. Only IIC-IID of E. coli and B. subtilis also support bacteriophage lambda infection. The six chimeric complexes had lost transport activity, but three containing IIC of E. coli or B. subtilis continue to support bacteriophage lambda infection. Complexes containing IIC(Man) and fusion proteins between truncated IID(Man) and alkaline phosphatase or beta-galactosidase support penetration of lambda DNA if less than 100 residues are missing from the C-terminus of IID(Man). Truncation of IIC(Man) renders the complex unstable. Taken together, these results suggest, that IIC is the major specificity determinant for lambda infection but that the IIC subunit is stably expressed only in a complex with the IID subunit. Lambda DNA in transit across the periplasmic space, but not transforming plasmid DNA, is inaccessible to the non-specific nuclease NucA of Anabaena sp. targeted to the periplasmic space either in soluble form or as a fusion protein to the C-terminus of IID(Man).     

Enhanced expression of bovine growth hormone gene by different culture conditions in Escherichia coli

To optimize the production of bovine growth hormone (bGH) in E. coli, the cells harboring pUBJ10 plasmid, which contains the modified 59-coding region of bGH cDNA under the control of trc promoter, was induced to express under various culture conditions such as medium (LB or M9CA), temperature, induction stage, expression time, IPTG concentration, and hosts. Induction stage was effective at early logarithmic phase. The expression levels of bGH were not largely affected by IPTG concentrations, slightly greater in LB medium than in M9CA medium, and efficient in 4 to 6 h of expression time. The highest level of bGH production was obtained in E. coli BL21 strain.     

The development of an efficient system for heterologous expression of cytochrome P450s in Escherichia coli using hemA gene co-expression

Biosynthesis of heme in Escherichia coli is under strict regulatory control since free heme or intermediates of its biosynthesis are potentially toxic for the cell. Under normal physiological conditions a bacterial cell does not have significant levels of free heme. Recombinant hemeproteins with affinity for heme lower than that of intrinsic cell proteins are often only isolated as apo-proteins. Moreover, for a number of hemeproteins expressed as apo-protein in E.coli it is not possible to reconstitute holo-protein in vitro. To circumvent these issues, fully active recombinant hemeproteins are usually expressed with expensive 5-aminolevulinic acid supplementation. In the present work, we construct the helper plasmid pHg expressing glutamyl-tRNA reductase (hemA) a key enzyme catalyzing the rate-limiting reaction in heme biosynthesis in E. coli, to avoid the necessity of 5-aminolevulinic acid supplementation. Overexpression of HemA restores the proper balance between protein and heme synthesis so that the newly synthesized recombinant apo-protein is continuously converted to holo-protein. The pHg plasmid is capable of supporting high-level expression of microsomal CYP1A1, CYP1A2, CYP21, CYP17, and mitochondrial CYP11A1. This new expression system provides a simple approach to obtain significant quantities of the active holo-form of recombinant hemeproteins.     

From famine to feast: the role of methylglyoxal production in Escherichia coli

The enzyme methylglyoxal synthase (MGS) was partially purified from Escherichia coli extracts, and the amino-terminal sequence of candidate proteins was determined, based on the native protein being a tetramer of about 69 kDa. Database analysis identified an open reading frame in the E . coli genome, YccG, corresponding to a protein of 16.9 kDa. When amplified and expressed from a controlled promoter, it yielded extracts that contained high levels of MGS activity. MGS expressed from the trc promoter accumulated to approximately 20% of total cell protein, representing approximately 900-fold enhanced expression. This caused no detriment during growth on glucose, and the level of methylglyoxal (MG) in the medium rose to only 0.08 mM. High-level expression of MGS severely compromised growth on xylose, arabinose and glycerol. A mutant lacking MGS was constructed, and it grew normally on a range of carbon sources and on low-phosphate medium. However, the mutant failed to produce MG during growth on xylose in the presence of cAMP, and growth was inhibited.     

Expression of a cDNA encoding a rat liver glutathione S-transferase Ya subunit in Escherichia coli

A full length cDNA clone, pGTB38 (C. B. Pickett et al. (1984) J. Biol. Chem. 259, 5182-5188), complementary to a rat liver glutathione S-transferase Ya mRNA has been expressed in Escherichia coli. The cDNA insert was isolated from pGTB38 using MaeI endonuclease digestion and was inserted into the expression vector pKK2.7 under the control of the tac promoter. Upon transformation of the expression vector into E. coli, two protein bands with molecular weights lower than the full-length Ya subunit were detected by Western blot analysis in the cell lysate of E. coli. These lower-molecular-weight proteins most likely result from incorrect initiation of translation at internal AUG codons instead of the first AUG codon of the mRNA. In order to eliminate the problem of incorrect initiation, the glutathione S-transferase Ya cDNA was isolated from the expression vector and digested with Bal31 to remove extra nucleotides from the 5' noncoding region. The protein expressed by this expression plasmid, pKK-GTB34, comigrated with the Ya subunit on sodium dodecyl sulfate polyacrylamide gels and was recognized by antibodies against the YaYc heterodimer. The expressed Ya homodimer was purified by S-hexylglutathione affinity and ion-exchange chromatographies. Approximately 50 mg pure protein was obtained from 9 liters of E. coli culture. The expressed Ya homodimer displayed glutathione-conjugating, peroxidase, and isomerase activities, which are identical to those of the native enzyme purified from rat liver cytosol. Protein sequencing indicates that the expressed protein has a serine as the NH2 terminus whereas the NH2 terminus of the glutathione S-transferase Ya homodimer purified from rat liver cytosol is apparently blocked.     

Facilitating the formation of disulfide bonds in the Escherichia coli periplasm via coexpression of yeast protein disulfide isomerase

Sacchromyces cerevisiae protein disulfide isomerase (yPDI) was expressed in the E. coli periplasm by using plasmids encoding the OmpA-yPDI-(His)(6) fusion gene under the control of the araBAD, trc, or T7 promoter. The expression levels of yeast PDI under these promoters were compared. Our results showed that yeast PDI expressed into the periplasm could catalyze the formation of disulfide bonds in alkaline phosphatase, restoring the phoA(+) phenotype in dsbA(-) mutants. The yeast PDI was purified from the Escherichia coli periplasm and shown to exhibit catalytic properties comparable to those of the rat enzyme with reduced RNase as substrate. In vivo, coexpression of the yeast PDI increased the yield of bovine pancreatic trypsin inhibitor (BPTI) in E. coli by 2-fold, similar to the effect seen previously with the coexpression of the rat enzyme. However yeast PDI was more effective than rat PDI in facilitating the expression of active tissue plasminogen activator (tPA). These results point to differences in the substrate specificity of various PDI enzymes, at least in the context of the E. coli periplasm.     

人脑源性神经营养因子基因的克隆及在大肠杆菌中表达

人脑源性神经营养因子基因的克隆及在大肠杆菌中表达何晓龙,路长林,王成海（第二军医大学神经生物学教研室,上海２００４３３）关键词神经营养因子;基因克隆脑源性神经营养因子（ｂｒａｉｎ－ｄｅｒｉｖｅｄｎｅｕｒｏｔｉｃ…ｉ。血。ｔｏｒ,ＢＤ贾助是Ｂａｄｅ等人...