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。     

Identification of vaccine candidate antigens of Staphylococcus aureus by serological proteome analysis

In this study we applied serological proteome analysis (Klade, C. S. et al. Proteomics 2001, 1, 890-898) for identification of bacterial vaccine candidate antigens. First, approximately one hundred sera from healthy individuals and patients suffering from Staphylococcus aureus infections were screened for antibodies against staphylococcal lysates and recombinant proteins representing surface antigens. Two pools (healthy donors, patients) each consisting of five sera with the highest antiproteinaceous IgG reactivity were selected. Second, S. aureus COL was grown under different conditions and the number of antigens expressed was monitored by Western blot analysis. Third, surface proteins were enriched by digesting the bacterial cell wall under isotonic conditions and subsequent removal of protoplasts. These protein preparations were resolved by two-dimensional electrophoresis (2-DE) (pI 4-7). 2-DE immunoblotting using the preselected serum pools at 1:10 000-1:100 000 dilutions revealed a number of highly immunogenic staphylococcal proteins. Twenty-one spots were isolated by preparative 2-DE, and analysed by matrix-assisted laser desorption/ionization mass spectrometry and tandem mass spectrometry sequencing of tryptic peptides. This led to the identification of 15 proteins including known and novel vaccine candidates. Seroreactivity of several antigens including serine-aspartate repeat containing protein D, immuno-dominant staphylococcal antigen and a novel 309 amino acid lipoprotein was independently confirmed by enzyme-linked immunosorbent assay and Western blot analysis of purified recombinant proteins. In conclusion, serological proteome analysis proved to be a powerful tool for the identification of novel staphylococcal antigens, which provide a basis for rational vaccine design.     

Overexpression, purification of poly-his-nuclease R and its potential use

A poly-histidine tag was engineered at the N-terminus of staphylococcal nuclease R. The new enzyme was over-expressed in Escherichia coli. The manipulation makes the enzyme, poly-his-nuclease R, to be easily separated and purified from other proteins. It has the same activity for non-specific hydrolysis of nucleic acids as the staphylococcal nuclease R at wide range of temperature and pH. The properties make it very useful to remove contaminated DNA/RNA from recombinant proteins during protein purification.     

Choice of the method for isolating conjugates of staphylococcal protein A with peroxidase for immunoenzyme analysis

An attempt to obtain the preparations of peroxidase-labeled staphylococcal protein A, intended for use in the enzyme immunoassay, by the glutaraldehyde method has failed. The modified periodate method permitting the preparation of active conjugates of staphylococcal protein A with peroxidase has been developed.     

Dissociation between murine spleen cell mitogenic activity of enterotoxin contaminants and anti-tumor activity of staphylococcal protein A

Soluble staphylococcal protein A (SpA) in the form of high m.w. complexes with IgG has been shown to significantly inhibit the growth of Meth A fibrosarcomas in BALB/c mice. Although SpA reportedly is a potent T cell mitogen that can induce immune cell proliferation and production of humoral factors with anti-tumor activity, it has been suggested that mitogenic enterotoxin contaminants might be responsible for these effects. The purpose of the present study was to investigate the nature of SpA-induced cell proliferation and the relationship between mitogenicity and the anti-tumor effect that we observed in our mouse model. SpA stimulated the proliferation of a mixed population of splenic B and T cells from BALB/c mice, but activity did not require the presence of IgG in the culture medium. Furthermore, mitogenic activity could be inhibited completely by anti-SEA plus anti-SEB, but was unaffected by anti-SpA. HPLC-purified SpA was inactive while the mitogenic factor(s) had the same retention time as authentic enterotoxin and its activity was inhibited by anti-SEA and anti-SEB, but not by anti-SpA. Enterotoxin-free rSpA produced in Escherichia coli had the same IgG binding capacity as the staphylococcal product but was not mitogenic. These data indicate that SEA and SEB completely account for mitogenicity in SpA preparations. In contrast, we found that optimal concentrations of rSpA as well as crude and HPLC purified staphylococcal SpA were equally effective in inhibiting the growth of established Meth A fibrosarcomas demonstrating that SpA is responsible for antitumor activity without any apparent role for enterotoxins.     

Preparation and properties of the staphylococcal toxin causing the toxic shock syndrome

A method is proposed for isolation and purification of the staphylococcal toxin causing the toxic shock syndrome (TSS). The method includes three steps: aggregation of protein from the cultural filtrate of Staphylococcus aureus strain 1169 in the presence of 0.025% sodium hexametaphosphate at pH 3.0; gel filtration of the concentrated material on the sephadex G75; ion-exchange chromatography on DEAE 32 cellulose. The proposed method permits to obtain the purified biologically active preparation of toxin with the yield about 40%. The obtained preparations are homogeneous in polyacrylamide electrophoresis and as analyzed by immunochemical methods. The mol mass of the isolated protein is 24 kD, it is not immunologically identical to staphylococcal toxins A-D and is lethal for New Zealand white rabbits and chinchilla rabbits. Interferon inducing activity of the protein is identical to the one of staphylococcal enterotoxin type A.     

Proteolytic degradation of fused protein A-β-galactosidase in Escherichia coli

The stability of the fusion protein staphylococcal protein A-E. coli β-galactosidase (SpA-βgal) produced in E. coli has been studied both in cell disintegrate and in purified preparations. SpA-βgal was degraded by a proteolytic cleavage between the two functional parts of the molecule, resulting in one β-galactosidase tetramer and four protein A molecules. Intermediates were detected, namely β-galactosidase containing three, two and one protein A. The β-galactosidase was stable with respect to enzyme activity and molecular weight, while protein A was further degraded. In cell disintegrate the half-life of SpA-βgal was found to be 6 h at 20°C and 1.5 h at 37°C. The protease responsible for initial proteolytic cleavage of SpA-βgal was shown to be cell debris associated.     

Experimental investigation of preparations for the immunotherapy of staphylococcal infections

A comparative experimental study was carried out of antigenic staphylococcal preparations developed in the USSR and Czechoslovakia for the immune therapy of chronic staphylococcal infection. The efficiency of the preparations was unequivocally confirmed using the rabbit staphylococcal sepsis model. The immunogenicity of tested strains was shown not to always correlate with their virulence. Preparations obtained by means of aqueous extraction from mildly virulent immunogenic strains exhibited greater protective activity than those prepared from highly virulent strains. The PCA phenomenon did not differ significantly provided the tested preparations were administered at doses which ensured equal protective action.     

Enzymatic lysis of the pseudomurein-containing methanogen Methanobacterium formicicum.

A streptomycete isolated from cow manure produces an extracellular enzyme capable of lysing the pseudomurein-containing methanogen Methanobacterium formicicum. The lytic activity has been partially purified from culture fluid and appears to be a serine protease. Similar lytic activity has been fractionated from pronase. Optimal conditions have been developed for lysis of M. formicicum by commercial preparations of proteinase K. The three lytic enzymes have been partially characterized. The results with the three enzyme preparations tend to confirm that proteolytic enzymes are capable of lysing methanogen cells.     

Production of a protein A--lymphotoxin hybrid protein for cancer-targeted therapy.

A hybrid protein between staphylococcal protein A and human lymphotoxin, ALT, was produced in Escherichia coli by expression of a recombinant plasmid containing the respective genes. IgG-binding activity of ALT was confirmed by Western blotting analysis and by affinity purification with IgG-Sepharose column chromatography. The purified ALT had cytotoxicity on mouse L-929 cells and its specific activity was approximately 3.5-5.0 X 10(6) U mg-1. ALT was partially degraded by a protease including in the E. coli lysate or trypsin and was converted to lymphotoxin which lacks the NH2-terminal 19 residues but possesses higher cytotoxic activity than ALT.     

Protective efficacy of combined administration of the multicomponent vaccine and the immunomodulator myelopid in experimental infections in mice

The influence of myelopid (MP) on the protective activity of polycomponent vaccine VP-4 prepared from the antigens of opportunistic bacteria was studied on experimental infections of mice, caused by Klebsiella pneumoniae, Salmonella typhimurium and Staphylococcus aureus. In staphylococcal and Klebsiella infections the joint administration of vaccine VP-4 and MP produced more pronounced protective effect than each of these preparations, introduced alone. The protective action of vaccine VP-4 was specially enforced by MP in cases of local staphylococcal infection. Recommendations on the joint use of two or more immunomodulating agents are possible only on the basis of the experimental substantiation of their effect in definite infections.     

Modes of action of β-mannanase enzymes of diverse origin on legume seed galactomannans

β-Mannanase activities in the commercial enzyme preparations Driselase and Cellulase, in culture solutions of Bacillus subtilis (TX1), in commercial snail gut (Helix pomatia) preparations and in germinated seeds of lucerne, Leucaena leucocephala and honey locust, have been purified by substrate affinity chromatography on glucomannan-AH-Sepharose. On isoelectric focusing, multiple protein bands were found, all of which had β-mannanase activity. Each preparation appeared as a single major band on SDS-polyacrylamide gel electrophoresis. The enzymes varied in their final specific activities, Km values, optimal pH, isoelectric points and pH and temperature stabilities but had similar MWs. The enzymes have different abilities to hydrolyse galactomannans which are highly substituted with galactose. The preparations Driselase and Cellulase contain β-mannanases which can attack highly substituted galactomannans at points of single unsubstituted d-mannosyl residues if the d-galactose residues in the vicinity of the bond to be hydrolysed are all on only one side of the main chain.     

Chromatofocusing: a new method for purification of staphylococcal enterotoxins B and C1.

A new chromatographic procedure was developed which obtained highly purified preparations of staphylococcal enterotoxins B and C1 in yields of 60% from cultures of Staphylococcus aureus and which is faster than any of the separation methods used previously. The procedure involves chromatography on carboxymethylcellulose, removal of alpha-toxin by adsorption to rabbit erythrocyte membranes, and finally, chromatofocusing as the fundamental new step. Enterotoxins were obtained in highly purified form and behaved in a homogeneous manner as determined by ultracentrifugation and electrophoresis on polyacrylamide gel in the presence of sodium dodecyl sulfate, with molecular weights of 34,000 for staphylococcal enterotoxin B and 30,000 for staphylococcal enterotoxin C1. Using chromatofocusing as the final purification step, we isolated three B and six C1 distinct but immunologically identical enterotoxin fractions, which were found to be devoid of any impurities and to possess a marked degree of toxicity in monkeys.     

Production and characterization of recombinant human neutrophil chemotactic factor

A putative mature human neutrophil chemotactic factor (NCF) corresponding to the C-terminal 72 amino acids of its precursor was directly produced in Escherichia coli by recombinant DNA technology. Human NCF was present in both the soluble and insoluble protein fractions of the homogenate of host cells, and it was partially purified as a water-soluble polypeptide from both fractions, separately. The partially purified NCF preparation was highly purified to an endotoxin-free homogeneous polypeptide by means of CM-Sepharose CL-6B column chromatography and gel filtration on Toyopearl HW-55. No difference between the human NCF preparations purified from both starting materials could be found concerning purity, primary structure, solubility, molecular weight, and chemotactic activity for human neutrophils. The amino acid sequence of recombinant human NCF was identical to the sequence deduced from the cDNA sequence. A methionine residue due to the translation initiation codon was removed. Recombinant human NCF was found to be biologically active and to exhibit chemotactic activity for human neutrophils in vitro and cause a neutrophil infiltration in vivo in mice.     

Chromatofocusing: a new method for purification of staphylococcal enterotoxins B and C1

A new chromatographic procedure was developed which obtained highly purified preparations of staphylococcal enterotoxins B and C1 in yields of 60% from cultures of Staphylococcus aureus and which is faster than any of the separation methods used previously. The procedure involves chromatography on carboxymethylcellulose, removal of alpha-toxin by adsorption to rabbit erythrocyte membranes, and finally, chromatofocusing as the fundamental new step. Enterotoxins were obtained in highly purified form and behaved in a homogeneous manner as determined by ultracentrifugation and electrophoresis on polyacrylamide gel in the presence of sodium dodecyl sulfate, with molecular weights of 34,000 for staphylococcal enterotoxin B and 30,000 for staphylococcal enterotoxin C1. Using chromatofocusing as the final purification step, we isolated three B and six C1 distinct but immunologically identical enterotoxin fractions, which were found to be devoid of any impurities and to possess a marked degree of toxicity in monkeys.     

Production and characterisation of recombinant forms of human pulmonary surfactant protein C (SP-C): Structure and surface activity

Surfactant protein C (SP-C) is an essential component for the surface tension-lowering activity of the pulmonary surfactant system. It contains a valine-rich alpha helix that spans the lipid bilayer, and is one of the most hydrophobic proteins known so far. SP-C is also an essential component of various surfactant preparations of animal origin currently used to treat neonatal respiratory distress syndrome (NRDS) in preterm infants. The limited supply of this material and the risk of transmission of infectious agents and immunological reactions have prompted the development of synthetic SP-C-derived peptides or recombinant humanized SP-C for inclusion in new preparations for therapeutic use. We describe herein the recombinant production in bacterial cultures of SP-C variants containing phenylalanines instead of the palmitoylated cysteines of the native protein, as fusions to the hydrophilic nuclease A (SN) from Staphylococcus aureus. The resulting chimerae were partially purified by affinity chromatography and subsequently subjected to protease digestion. The SP-C forms were recovered from the digestion mixtures by organic extraction and further purified by size exclusion chromatography. The two recombinant SP-C variants so obtained retained more than 50% alpha-helical content and showed surface activity comparable to the native protein, as measured by surface spreading of lipid/protein suspensions and from compression pi-A isotherms of lipid/protein films. Compared to the protein purified from porcine lungs, the recombinant SP-C forms improved movement of phospholipid molecules into the interface (during adsorption), or out from the interfacial film (during compression), suggesting new possibilities to develop improved therapeutic preparations.     

Effect of human recombinant interferon on cytotoxic activity of natural killer (NK) cells and monocytes

Studies have been performed on the in vitro immunologic effects of homogeneous recombinant human leukocyte interferon, IFLrA. Large granular lymphocytes, enriched for natural killer (NK) cell activity, were pretreated wtih IFLrA or natural interferon preparations and then tested for augmentation of NK activity and of antibody-dependent cell-mediated cytoxicity (ADCC). Monocytes were tested for cytolytic and cytostatic activity in 48–72 hr radioisotopic assays performed in the presence or absence of interferon. Treatment with IFLrA caused significant augmentation of NK, ADCC, and monocyte-mediated cytotoxic activities. Even 10 units of IFLrA induced augmentation of NK activity, and 100 units or more boosted monocyte-mediated activity. The effects in each of these assays were species-specific, with no detectable effects on the activity of mouse effector cells. These results indicate that homogeneous recombinant interferon has potent in vitro immunomodulating effects and thus provide a basis for carefully examining the in vivo effects of this protein on host defenses in forthcoming clinical trials with cancer patients.     

Purification of recombinant activin A using the second follistatin domain of follistatin-related gene (FLRG)

Activins are multifunctional growth factors belonging to the transforming growth factor-beta superfamily. Isolation of activins from natural sources requires many steps and only produces limited quantities. Even though recombinant preparations have been used in recent studies, purification of recombinant activins still requires multiple steps. To purify recombinant activin A, we have developed a simple method using the second follistatin domain of an activin-binding protein follistatin-related gene (FLRG). An affinity column was prepared with a partial FLRG fusion protein. The partial FLRG protein contained the second follistatin domain and the C-terminus acidic domain, and was tagged with six histidine residues at its N-terminus. The fusion protein was expressed in Escherichia coli and purified with nickel affinity column. Thereafter, the purified fusion protein was coupled to NHS-activated column. Recombinant activin A was produced in Chinese hamster ovary (CHO) cells, which were stably transfected with rat inhibin/activin betaA-subunit cDNA. After 48-h suspension culture of the cells in a serum free medium, the culture media was recovered and passed through the FLRG-coupled column. After washing with phosphate-buffered saline, bound protein was eluted out with an acidic buffer. Any significant contaminations were not detected when the purified protein was analyzed by SDS-PAGE. Apparent sizes of the protein were 14 and 28 kDa under the reduced and non-reduced conditions, respectively. Western blot analysis confirmed that the purified protein was activin A. The purified recombinant activin stimulated p3TP-lux reporter activity in CHO cells and follicle-stimulating hormone secretion from rat pituitary cells.     

Enzymic interesterification of fats: Laboratory and pilot-scale studies with immobilized lipase from Rhizopus arrhizus

An immobilized lipase suitable for fat interesterification has been prepared by precipitation with acetone of a commercial lipase from Rhizopus arrhizus onto diatomaceous earth. As observed previously with a less active enzyme from Aspergillus sp., the interesterification activity was enhanced by addition of purified lipase or by high loadings of commercial enzyme. The interesterification activities reached maximum values in both cases. For immobilized preparations with purified enzyme, interesterification activity was also enhanced by the presence of a precoat of glutaraldehyde cross-linked commercial lipase. A 2.9-L column of immobilized lipase was used to interesterify batches of shea oleine (67 kg) and shea oil (40 kg). Little activity was lost processing shea oleine, but slow poisoning of the bed occurred when shea oil was fed to the column.     

Kinetic properties of human dopamine sulfotransferase (SULT1A3) expressed in prokaryotic and eukaryotic systems: comparison with the recombinant enzyme purified from Escherichia coli.

Sulfation, catalyzed by members of the sulfotransferase enzyme family, is a major metabolic pathway which modulates the biological activity of numerous endogenous and xenobiotic chemicals. A number of these enzymes have been expressed in prokaryotic and eukaryotic systems to produce protein for biochemical and physical characterization. However, the effective use of heterologous expression systems to produce recombinant enzymes for such purposes depends upon the expressed protein faithfully representing the "native" protein. For human sulfotransferases, little attention has been paid to this despite the widespread use of recombinant enzymes. Here we have validated a number of heterologous expression systems for producing the human dopamine-metabolizing sulfotransferase SULT1A3, including Escherichia coli, Saccharomyces cerevisiae, COS-7, and V79 cells, by comparison of Km values of the recombinant enzyme in cell extracts with enzyme present in human platelets and with recombinant enzyme purified to homogeneity following E. coli expression. This is the first report of heterologous expression of a cytosolic sulfotransferase in yeast. Expression of SULT1A3 was achieved in all cell types, and the Km for dopamine under the conditions applied was approximately 1 microM in all heterologous systems studied, which compared favorably with the value determined with human platelets. We also determined the subunit and native molecular weights of the purified recombinant enzyme by SDS-PAGE, electrospray ionization mass spectrometry, dynamic light scattering, and sedimentation analysis. The enzyme purified following expression in E. coli existed as a homodimer with Mr approximately 68,000 as determined by light scattering and sedimentation analysis. Mass spectrometry revealed two species with experimentally determined masses of 34,272 and 34,348 which correspond to the native protein with either one or two 2-mercaptoethanol adducts. We conclude that the enzyme expressed in prokaryotic and eukaryotic heterologous systems, and also purified from E. coli, equates to that which is found in human tissue preparations.