Protein A-mouse acidic mammalian chitinase-V5-His expressed in periplasmic space of Escherichia coli possesses chitinase functions comparable to CHO-expressed protein

Acidic mammalian chitinase (AMCase) has been shown to be associated with asthma in mouse models, allergic inflammation and food processing. Here, we describe an E. coli-expression system that allows for the periplasmic production of active AMCase fused to Protein A at the N-terminus and V5 epitope and (His)6 tag (V5-His) at the C-terminus (Protein A-AMCase-V5-His) in E. coli. The mouse AMCase cDNA was cloned into the vector pEZZ18, which is an expression vector containing the Staphylococcus Protein A promoter, with the signal sequence and truncated form of Protein A for extracellular expression in E. coli. Most of the Protein A-AMCase-V5-His was present in the periplasmic space with chitinolytic activity, which was measured using a chromogenic substrate, 4-nitrophenyl N,N'-diacetyl-β-D-chitobioside. The Protein A-AMCase-V5-His was purified from periplasmic fractions using an IgG Sepharose column followed by a Ni Sepharose chromatography. The recombinant protein showed a robust peak of activity with a maximum observed activity at pH 2.0, where an optimal temperature was 54°C. When this protein was preincubated between pH 1.0 and pH 11.0 on ice for 1 h, full chitinolytic activity was retained. This protein was also heat-stable till 54°C, both at pH 2.0 and 7.0. The chitinolytic activity of the recombinant AMCase against 4-nitrophenyl N,N'-diacetyl-β-D-chitobioside was comparable to the CHO-expressed AMCase. Furthermore, the recombinant AMCase bound to chitin beads, cleaved colloidal chitin and released mainly N,N'-diacetylchitobiose fragments. Thus, the E. coli-expressed Protein A-mouse AMCase-V5-His fusion protein possesses chitinase functions comparable to the CHO-expressed AMCase. This recombinant protein can be used to elucidate detailed biomedical functions of the mouse AMCase.

[Cloning, expression and screening tandem repeats of the Z domain of Staphylococcus aureus protein A]

To screen an efficient recombinant Staphylococcus aureus protein A (SpA) for preparing matrix for affinity purification of immunoglobulin G (IgG), a genetic engineering approach was used to obtain monomer, two, three, four and five tandem repeats genes of the Z domain of SpA, then the genes were cloned into expression vector pET-22b and subsequently expressed in Escherichia coli BL21 (DE3). After induction with lactose, the target proteins were purified by Ni2+ affinity chromatography. The proteins with two, three, four and five tandem repeats of the Z domain were then coupled to CNBr-activated Sepharose 4B as an affinity chromatography matrix for affinity purification of human IgG. Furthermore, the differences in protein yield and IgG-binding capacity at different recombinant proteins were analyzed. The target proteins with monomer and tandem repeats of the Z domain had an effective expression in the genetic engineering bacteria. IgG could be specifically absorbed from human plasma by affinity chromatography. The protein yield and amount of IgG absorption of per mole protein could be improved by increasing the tandem repeats number of the Z domain. Compared with other tandem repeats, four tandem repeats of the Z domain exhibited more protein yield (160 mg/10 g wet cells) and higher level of IgG absorption (34.4 mg human IgG/mL gel). Therefore, four tandem repeats of the Z domain is more suitable for preparing matrix for affinity purification of IgG.

Large-scale transfection of mammalian cells

The large-scale transfection of mammalian cells allows moderate (milligram to gram) amounts of recombinant proteins (r-proteins) to be obtained for fundamental or clinical research. In this article, we describe a one-liter transfection using polyethyleneimine (PEI) for DNA delivery into human embryonic kidney (HEK-293) cells cultivated in serum-free suspension to produce a recombinant human monoclonal antibody that yields up to about 1 g/L in a 10-day process. The method is based on a DNA delivery step performed at high cell density (20×10(6) cells/mL) by direct addition of DNA and PEI to the culture. Subsequently, the cells are diluted 20-fold for the 10-day production phase in the presence of valproic acid (VPA), a histone deacetylase inhibitor. The methods for plasmid purification, antibody quantification by enzyme-linked immunosorbent assay (ELISA), and affinity purification with protein A are also described.

Antibody-mediated targeted gene transfer to NMDA NR1-containing neurons in rat neocortex by helper virus-free HSV-1 vector particles containing a chimeric HSV-1 glycoprotein C-staphylococcus A protein

Because of the heterogeneous cellular composition of the brain, and especially the forebrain, cell type-specific expression will benefit many potential applications of direct gene transfer. The two prevalent approaches for achieving cell type-specific expression are using a cell type-specific promoter or targeting gene transfer to a specific cell type. Targeted gene transfer with Herpes Simplex Virus (HSV-1) vectors modifies glycoprotein C (gC) to replace the heparin binding domain, which binds to many cell types, with a binding activity for a specific cell surface protein. We previously reported targeted gene transfer to nigrostriatal neurons using chimeric gC-glial cell line-derived neurotrophic factor or gC-brain-derived neurotrophic factor protein. Unfortunately, this approach is limited to cells that express the cognate receptor for either neurotrophic factor. Thus, a general strategy for targeting gene transfer to many different types of neurons is desirable. Antibody-mediated targeted gene transfer has been developed for targeting specific virus vectors to specific peripheral cell types; a specific vector particle protein is modified to contain the Staphylococcus A protein ZZ domain, which binds immunoglobulin (Ig) G. Here, we report antibody-mediated targeted gene transfer of HSV-1 vectors to a specific type of forebrain neuron. We constructed a chimeric gC-ZZ protein, and showed this protein is incorporated into vector particles and binds Ig G. Complexes of these vector particles and an antibody to the NMDA receptor NR1 subunit supported targeted gene transfer to NR1-containing neocortical neurons in the rat brain, with long-term (2 months) expression.

The role of Staphylococcus aureus surface protein SasG in adherence and biofilm formation

Staphylococcus aureus colonizes the moist squamous epithelium of the anterior nares. One of the adhesins likely to be responsible is the S. aureus surface protein G (SasG), which has sequence similarity with the proteins Pls (plasmin sensitive) of S. aureus and Aap (accumulation associated protein) of Staphylococcus epidermidis. Expression of SasG by a laboratory strain of S. aureus could not be detected by Western immunoblotting. To enable investigation of SasG, the gene was cloned into two expression vectors, the IPTG-inducible pMUTIN4 and the tetracycline-inducible pALC2073, and introduced into S. aureus. Expression of SasG masked the ability of exponentially grown S. aureus cells expressing protein A (Spa), clumping factor B (ClfB) and the fibronectin binding proteins A and B (FnBPA and FnBPB) to bind to IgG, cytokeratin 10 and fibronectin, respectively. SasG also masked binding to fibrinogen mediated by both ClfB and the FnBPs. Western immunoblotting showed no reduction in expression of the blocked adhesins following induction of SasG. SasG size variants with eight, six or five B repeats masked binding to the ligands, whereas variants with four, two or one repeats had no effect. SasG-expressing strains formed peritrichous fibrils (53.47+/-2.51 nm long) of varying density on the cell wall, which were labelled by immunogold negative staining with anti-SasG antibodies. SasG-expressing strains of S. aureus also formed biofilm independently of the polysaccharide intercellular adhesin (PIA). SasG variants with eight, six and five repeats formed biofilm, whereas variants with four, two or one repeats did not. It was concluded that the fibrillar nature of SasG explains its ability to mask binding of S. aureus microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) to their ligands and to promote formation of biofilm. In addition, the strong adhesion of SasG to desquamated nasal epithelial cells likely compensates for its blocking of the binding of S. aureus ClfB to cytokeratin 10, which is important in adhesion to squames by cells lacking SasG. Several clinical isolates expressed SasG at levels similar to those of SH1000 sasG : : pMUTIN4, indicating that the properties described in the laboratory strain SH1000 may be relevant in vivo.

Regulation of exoprotein gene expression by the Staphylococcus aureus cvfB gene

We previously reported that the cvfB gene (SA1223) of Staphylococcus aureus is responsible for the virulence of this pathogenic bacterium. We show here that the cvfB gene regulates exoprotein gene expression. In a cvfB gene deletion mutant, hemolysin, DNase, and protease production were decreased, whereas protein A expression was increased. The amount of RNAIII, the transcript from the P3 promoter in the agr locus that regulates the expression of various virulence factors, was also reduced in the cvfB mutant. In addition, P2 and P3 promoter activity in the agr locus was decreased in the mutant. Under the genetic background of the agr-null mutation, cvfB gene disruption decreased the production levels of DNase and protease. Moreover, the cvfB and agr double mutant was less virulent than the agr mutant in silkworms. These results suggest that the cvfB gene product contributes to the expression of virulence factors and to pathogenicity via both agr-dependent and agr-independent pathways.

Synthesis, Expression and Purification of a Type of Chlorotoxin-like Peptide from the Scorpion, Buthus martensii Karsch, and its Acute Toxicity Analysis

A gene, rBmK Cta, encoding a chlorotoxin-like peptide from the scorpion, Buthus martensii Karsch, was synthesized according to the sequence optimized for codon usage in Escherichia coli and was expressed in E. coli BL21 (DE3) using a pExSecI expression system in which the IgG-binding domain-ZZ of protein A is fused to the N-terminal of rBmK CTa. The fusion protein, ZZ-rBmK CTa, was expressed in soluble form (7.8 mg l(-1)) and was purified to give a single band on SDS-PAGE. The domain-ZZ of fusion protein ZZ-rBmK CTa was removed by cleavage of an Asn-Gly peptide bond with hydroxylamine. The rBmK CTa was separated from the IgG-binding moiety by a second passage through the IgG affinity column. Western blot analysis demonstrated that this protein was rBmK CTa. Acute toxicity assay in mice demonstrated that the rBmK CTa had an LD(50) value of 4.3 mg kg(-1).

Inexpensive and generic affinity purification of recombinant proteins using a family 2a CBM fusion tag

The selective binding of the family 2a carbohydrate binding module (CBM2a) of xylanase 10A of the soil bacterium Cellulomonas fimi to a variety of cellulosic substrates is shown to provide a new, cost-effective affinity chromatography system for purification of recombinant protein. Genetic linkage of CBM2a to a target protein, in this case protein A from Staphylococcus aureus, results in a fusion protein that binds strongly to the particulate-cellulose resin Avicel PH101 and retains the biological activity of the fusion partner. Affinity purification of protein A-CBM2a from the supernatant of a recombinant E. coli JM101 culture results in a product purity of greater than 95% and a product concentration factor of 34 +/- 3. Measured column parameters are combined with one-dimensional equations governing continuity and intraparticle diffusion to predict product breakthrough curves with good accuracy over the range of realistic operating conditions. Peak spreading within the column is controlled by intraparticle diffusion for CBM2a and by a combination of film mass transfer and intraparticle diffusion for the larger protein A-CBM2a fusion protein.

Protein A gene expression is regulated by DNA supercoiling which is modified by the ArlS-ArlR two-component system of Staphylococcus aureus

Bacterial pathogens such as Staphylococcus aureus undergo major physiological changes when they infect their hosts, requiring the coordinated regulation of gene expression in response to the stresses encountered. Several environmental factors modify the expression of S. aureus virulence genes. This report shows that the expression of spa (virulence gene encoding the cell-wall-associated protein A) is down-regulated by high osmolarity (1 M NaCl, 1 M KCl or 1 M sucrose) in the wild-type strain and upregulated by novobiocin (a DNA gyrase inhibitor that relaxes DNA). A gyrB142 allele corresponding to a double mutation in the B subunit of DNA gyrase relaxed DNA and consequently induced spa expression, confirming that spa expression is regulated by DNA topology. Furthermore, in the presence of novobiocin plus 1 M NaCl, a good correlation was observed between DNA supercoiling and spa expression. The ArlS-ArlR two-component system is involved in the expression of virulence genes such as spa. Presence of an arlRS deletion decreased the effect of DNA supercoiling modulators on spa expression, suggesting that active Arl proteins are necessary for the full effect of DNA gyrase inhibitors and high osmolarity on spa expression. Indeed, evidence is provided for a relationship between the arlRS deletion and topological changes in plasmid DNA.

[Protein a production in coagulase-negative or clumping factor (CF)-negative isolates of Staphylococcus aureus]

The aim of study was to determine a production of proteinA in coagulase-negative Staphylococcus aureus (CNSA) or CF-negative S. aureus (CFNSA) strains. 59 CNSA and 18 CFNSA strains were isolated between 1997 and 2003 from different clinical specimens. The Protein A production was determined by immunoblotting method. The presence of protein A gene (spa) was investigated using the polymerase chain reaction (PCR). Two sets of phages and RFLP (Restriction Fragment Lenth Polymorphism) of coa gene method were used for typing strains. The results proved that the lack of ability of protein A production occurs more frequently in protein A-negative CFNSA strains with compare to the CNSA, which are protein A-positive for the majority of strains. Deficiencies of protein A, doesn't seem to be caused by the loss of spa gene. Protein A-negative CFNSA strains have phagotypes, RFLP and antibiotic resistant patterns which differ them from protein A-negative CNSA strains. Almost all of protein A-negative CFNSA and CNSA strains are resistant to methicillin.

Use of Microfiltration as First Step in Recovery of Protein A From Fermentation Broth

The flux and transmission of protein A during microfiltration have been studied. We studied the performance of two commercial membranes: one made of nylon (Pall Ultipore Nylon66, 0.2 microm) and one of polyether sulfone (Pall Omega, 0.16 microm). The Nylon66 membrane had by far the best transmission of protein A although a previous study showed that bovine serum albumin (BSA), often used to characterize membranes, had much better transmission through the Omega membrane. The membrane manufacturer also states that the Omega membrane is the best membrane for this kind of application because it is a low-protein-binding membrane. The lower transmission of the Omega membrane for protein A was assumed to be owing to its smaller pores and higher charge density in combination with the larger Stokes radius for protein A. When the pH was lowered, the Nylon66 membrane still had the higher transmission. It can thus be concluded that a membrane that is found suitable for the recovery process of one protein is not always the best choice for the recovery process for other proteins even though the membrane is low protein binding.

Correlation of acetate catabolism and growth yield in Staphylococcus aureus: implications for host-pathogen interactions

Recently, we reported that the prototypical Staphylococcus aureus strain RN6390 (a derivative of NCTC 8325) had significantly reduced aconitase activity relative to a diverse group of S. aureus isolates, leading to the hypothesis that strain RN6390 has impaired tricarboxylic acid (TCA) cycle-mediated acetate catabolism. Analysis of the culture supernatant from RN6390 confirmed that acetate was incompletely catabolized, suggesting that the ability to catabolize acetate can be lost by S. aureus. To test this hypothesis, we examined the carbon catabolism of the S. aureus strains whose genome sequences are publicly available. All strains catabolized glucose and excreted acetate into the culture medium. However, strains NCTC 8325 and N315 failed to catabolize acetate during the postexponential growth phase, resulting in significantly lower growth yields relative to strains that catabolized acetate. Strains NCTC 8325 and RN6390 contained an 11-bp deletion in rsbU, the gene encoding a positive regulator of the alternative sigma factor sigma(B) encoded by sigB. An isogenic derivative strain of RN6390 containing the wild-type rsbU gene had significantly increased acetate catabolism, demonstrating that sigma(B) is required for acetate catabolism. Taken together, the data suggest that naturally occurring mutations can alter the ability of S. aureus to catabolize acetate, a surprising discovery, as TCA cycle function has been demonstrated to be involved in the virulence, survival, and persistence of several pathogenic organisms. Additionally, these mutations decrease the fitness of S. aureus by reducing the number of progeny placed into subsequent generations, suggesting that in certain situations a decreased growth yield is advantageous.

Modeling of the controlled expression of a harmful protein by a three-plasmid harboring system

A genetically structured mathematical model was developed and used to evaluate the influence of molecular parameters involved in the expression of a harmful recombinant protein (SPA::EcoRI). The system consists of the controlled expression of the endonuclease EcoRI cloned in the plasmid pMTC48. The control is exerted by the lambda CI repressor expressed from the plasmid pRK248cIts. The deleterious effect of the activity of the enzyme EcoRI on the host DNA is prevented by the action of the EcoRI methylase that is expressed constitutively from a third plasmid, pEcoR4. The model includes molecular mechanisms involved in the regulation of the expression of these genes and is used to determine cultural conditions that maximize the production of the recombinant protein.

Differential display identifies neuroendocrine-specific protein-A (NSP-A) and interferon-inducible protein 10 (IP-10) as ethanol-responsive genes in the fetal rat brain

Fetal alcohol exposure is the most common nonhereditary cause of mental retardation in the western world. Rats prenatally treated with ethanol liquid diet exhibit extensive defects in the brain that accurately model those observed in humans. To analyze the ethanol effects on gene expression during brain development, we performed mRNA differential display and two-dimensional electrophoresis on gestational day (G) 13 and G 16 brain from rats treated with ethanol liquid diet. Using mRNA differential display followed by a variety of quantitative analyses, three genes were confirmed to be ethanol-responsive. Among them was Neuroendocrine-Specific Protein-A (NSP-A), which is known to be affected by thyroid hormone in the cortex at this developmental time. However, two additional genes known to be thyroid hormone-responsive were unaffected by ethanol, indicating that interference with thyroid hormone action may not be a predominant pathway by which alcohol induces damage in the fetal brain. The observation that interferon-inducible protein-10 (IP-10) is up-regulated in ethanol-treated fetal brain may indicate the presence of a disease process recruiting CD8+ T-cells capable of interfering with myelination. The result of two-dimensional (2D) electrophoresis and Western analyses demonstrated that few changes in the abundance of individual proteins or the phosphorylation of proteins at threonine and tyrosine were induced by prenatal ethanol exposure. A critical analysis of the approaches used in the present study may be important for future studies in this field.

Variation of the agr locus in Staphylococcus aureus isolates from cows with mastitis

Staphylococcus aureus isolates from mastitic cow's milk were examined for production of alpha-hemolysin and protein A and their accessory gene regulator (agr locus) was analyzed. An inverse relationship between alpha-hemolysin and protein A production was found in most of the 76 isolates, suggesting that the isolates tested may be classified into group I (high alpha-hemolysin/low protein A), II (low alpha-hemolysin/high protein A), or III (low alpha-hemolysin/low protein A). The agr locus, which consists of hld, agrB, agrD, agrC, and agrA, was detected in most of the 78 isolates including two reference strains (Wood 46 and Cowan I) by polymerase chain reaction (PCR). When the PCR products for agr locus of 22 isolates from groups I and II were digested with restriction enzyme MboI, seven bands of the expected lengths were recognized in strain Wood 46, but not in the other isolates tested. Nucleotide sequence analysis of PCR products from six isolates revealed that the agr locus sequence of strain Wood 46 corresponded to that of the published sequence data, but the other five isolates from groups I and II diverged at agrB and agrD sequences and thus the deduced amino acid sequences. These variations of agr locus in S. aureus bovine isolates differed from those reported by Ji et al. [Science 276 (1997) 2027].

SarS, a SarA homolog repressible by agr, is an activator of protein A synthesis in Staphylococcus aureus

The expression of protein A (spa) is repressed by global regulatory loci sarA and agr. Although SarA may directly bind to the spa promoter to downregulate spa expression, the mechanism by which agr represses spa expression is not clearly understood. In searching for SarA homologs in the partially released genome, we found a SarA homolog, encoding a 250-amino-acid protein designated SarS, upstream of the spa gene. The expression of sarS was almost undetectable in parental strain RN6390 but was highly expressed in agr and sarA mutants, strains normally expressing high level of protein A. Interestingly, protein A expression was decreased in a sarS mutant as detected in an immunoblot but returned to near-parental levels in a complemented sarS mutant. Transcriptional fusion studies with a 158- and a 491-bp spa promoter fragment linked to the xylE reporter gene disclosed that the transcription of the spa promoter was also downregulated in the sarS mutant compared with the parental strain. Interestingly, the enhancement in spa expression in an agr mutant returned to a near-parental level in the agr sarS double mutant but not in the sarA sarS double mutant. Correlating with this divergent finding is the observation that enhanced sarS expression in an agr mutant was repressed by the sarA locus supplied in trans but not in a sarA mutant expressing RNAIII from a plasmid. Gel shift studies also revealed the specific binding of SarS to the 158-bp spa promoter. Taken together, these data indicated that the agr locus probably mediates spa repression by suppressing the transcription of sarS, an activator of spa expression. However, the pathway by which the sarA locus downregulates spa expression is sarS independent.

Effects of amoxicillin, gentamicin, and moxifloxacin on the hemolytic activity of Staphylococcus aureus in vitro and in vivo

In Staphylococcus aureus infection hemolysis caused by the extracellular protein alpha-toxin encoded by hla is thought to contribute significantly to its multifactorial virulence. In vitro, subinhibitory concentrations of beta-lactam antibiotics and fluoroquinolones increase the levels of hla and alpha-toxin expression, whereas aminoglycosides decrease the levels of hla and alpha-toxin expression. In the present study we investigated the effects of subinhibitory concentrations of amoxicillin, gentamicin, and moxifloxacin on hla and alpha-toxin expression and total hemolysis of S. aureus strain 8325-4, a high-level alpha-toxin producer, and its alpha-toxin-negative mutant, DU 1090, in vitro and in a rat model of chronic S. aureus infection. The levels of expression of hla and alpha-toxin and total hemolysis did not differ significantly when amoxicillin, gentamicin, or moxifloxacin was added to cultures of S. aureus strain 8325-4. In vivo, strain 8325-4 induced a significantly increased level of hemolysis in infected pouches compared to that in uninfected control pouches, but the hemolysis was reduced to control levels by treatment with doses of amoxicillin, gentamicin, or moxifloxacin that reduced bacterial numbers by 2 orders of magnitude. Additionally, the effects of subinhibitory concentrations of the three antibiotics on total hemolysis of four methicillin-resistant S. aureus and three methicillin-sensitive S. aureus (MSSA) clinical isolates were assessed in vitro. A significant increase in total hemolysis was observed for only one MSSA strain when it was treated with amoxicillin but not when it was treated with moxifloxacin or gentamicin. When purified alpha-toxin was incubated with purified human neutrophil elastase, alpha-toxin was cleaved nearly completely. The results suggest that the penicillin-induced increases in S. aureus alpha-toxin expression are strain dependent, that reduction of bacterial numbers in vivo counteracts this phenomenon effectively, and finally, that in localized S. aureus infections alpha-toxin activity is controlled by neutrophil elastase.

Antenatal dexamethasone enhances surfactant protein synthesis in the hypoplastic lung of nitrofen-induced diaphragmatic hernia in rats

BACKGROUND/PURPOSE

Pulmonary hypoplasia is one of the main causes for the high mortality rate in patients with congenital diaphragmatic hernia (CDH). The expression of surfactant protein A in the hypoplastic CDH lung is reduced, and its concentration is decreased in the amniotic fluid of pregnancies complicated by CDH. In a CDH experimental model, prenatal glucocorticoid treatment has proved its efficacy in correcting the parameters of pulmonary biochemical and morphologic immaturity. The aim of this study was to investigate whether maternal administration of dexamethasone has any effect on the expression of surfactant protein A and surfactant protein B in nitrofen-induced experimental CDH rat model.

METHODS

CDH was induced in pregnant rats after administration of 100 mg of nitrofen on day 9.5 of gestation (term, 22 days). Dexamethasone (Dex, 0.25 mg/kg) was given by intraperitoneal injection on days 18.5 and 19.5 of gestation. Cesarean section was performed on day 21 of gestation. The fetuses were divided into 3 groups: group I, control (n = 16); group II, nitrofen-induced CDH (n = 16); group III, nitrofen-induced CDH with antenatal Dex treatment (n = 16). Indirect immunohistochemistry was performed using alkaline-phosphatase-coagulated streptavidin using anti-SP-A and anti-SP-B polyclonal antibodies. Reverse transcription polymerase chain reaction (RT-PCR) was performed to evaluate relative amount of SP-A and SP-B mRNA expression.

RESULTS

In the CDH lung (group II) we observed a markedly reduced number of type II pneumocytes positive for SP-A, and SP-B was increased to a level close to that of the control group. The relative amount of SP-A and SP-B was reduced significantly in group II compared with controls (P < .05) and significantly increased in group III compared with group II animals (P < .01).

CONCLUSION

These results suggest that antenatal glucocorticoid treatment increases the production of surfactant proteins in the CDH hypoplastic lung.

Agr-independent regulation of fibronectin-binding protein(s) by the regulatory locus sar in Staphylococcus aureus

Fibronectin-binding proteins (FnBPs) are thought to be important for the attachment of Staphylococcus aureus during infection. The regulation of the genes fnbA and fnbB by the global regulatory loci sar and agr was examined using site-specific regulatory mutants of S. aureus strain Newman. The results from binding assays using both aqueous and solid-phase fibronectin as well as ligand blotting with biotinylated fibronectin showed that the expression of FnBPA is enhanced in the agr mutant but inhibited in the sar mutant and the sar-agr double mutant. The same regulatory pattern was observed in Northern blot analysis using fnbA-specific probes. The introduction of sar on a multicopy plasmid increased the already enhanced fnbA transcription of the agr mutant. FnBPB was not detectable by ligand blotting and the fnbB promoter activity in promoter fusion assays was not affected by either sar or agr. The sequence encompassing ORF3 located upstream of sarA was found to be essential for the activation of fnbA transcription. We hypothesize that this sequence may modulate SarA expression and/or activity on the post-transcriptional level. Gel shift assays demonstrated that SarA binds to the fnbA promoter fragments, probably as a dimer. DNase I footprinting assays with SarA revealed a protected area of 102 bp upstream of fnbA.

Site-directed lipid modification of IgG-binding protein by intracellular bacterial lipoprotein process

IgG-binding protein was genetically expressed and lipid-modified in a site-directed manner in Escherichia coli. The DNA sequence encoding the signal peptide and the nine N-terminal amino acid residues of the major lipoprotein of E. coli (lpp) was fused to the sequence of B-domain which was one of the IgG binding domains of Staphylococcal Protein A (SpA). The N-terminal cysteine residue of the resulting protein was enzymatically linked with lipids in the bacterial membrane. The lipid-modified protein was translocated at the bacterial membrane in a manner similar to native bacterial lipoprotein, and it was purified with IgG-Sepharose by affinity chromatography. The lipid modified proteins (lppB1 and lppB5) showed a similar IgG binding activity to unmodified proteins, which was estimated by competitive ELISA. Proteoliposomes of lipid modified proteins were prepared in an elegant fashion so that the IgG binding site should be properly oriented on the surface of an individual liposome by anchoring the lipid-tail into the hydrophobic layer of the liposome membrane. As compared with the unmodified one, the lipid modified protein incorporated into the proteoliposome exhibited higher IgG binding activity.

Staphylococcus aureus isolates from patients with Kawasaki disease express high levels of protein A

Kawasaki disease (KD) is an acute vasculitis of young children that can be complicated by coronary artery abnormalities. Recent findings suggest that a superantigen(s) may play an important role in stimulating the immune activation associated with the disease, although the origin of this superantigen(s) is unclear. Staphylococcus aureus, isolated from the rectum or pharynx of patients with KD, secretes toxic shock syndrome toxin 1 (TSST-1). The KD isolates express low levels of other exoproteins compared to isolates from patients with toxic shock syndrome (TSS). Thus, it was previously suggested that the KD isolates may be defective in the global regulatory locus agr (for accessory gene regulator), which positively regulates these factors (D. Y. M. Leung et al., Lancet 342:1385-1388, 1993). Here we describe another characteristic of KD isolates. When considered collectively, the KD isolates were found to express higher levels of staphylococcal protein A than the TSS isolates, another characteristic of an agr-defective phenotype. This correlated with a higher level of spa mRNA in these isolates. In contrast, the KD and TSS isolates expressed comparable levels of TSST-1, consistent with previous findings (D. Y. M. Leung et al., Lancet 342:1385-1388, 1993). Analysis of RNAIII transcript levels and nucleotide sequence analysis of the RNAIII-coding region suggested that the KD isolates are not defective in RNAIII, the effector molecule of the agr regulatory system. However, induction of RNAIII transcription in the KD isolates did not result in a dramatic decrease in the amount of spa mRNA, as has been reported for other strains (F. Vandenesch, J. Kornblum, and R. P. Novick, J. Bacteriol. 173:6313-6320, 1991).

Spectroscopic investigation of tertiary fold of staphylococcal protein A to explore its engineering application

Staphylococcal protein A is a cell wall constituent of most strains of Staphylococcus aureus, and it is characterized by its binding affinity to some immunological classes. A mutated low molecular weight type protein A (LPA; Mwt = 27 kDa) which consists of the domains, E, D, A, B and 13 residues of the C-domain was prepared in this study. Since LPA does not possess a cell wall-bound region in contrast to wild-type protein A (WPA; Mwt = 42 kDa), we have established a methodology of large scale purification of LPA without using any extracellular expression systems such as Escherichia coli. Using this relatively abundant protein, the immobilization of the LPA with silk fibroin of Bombyx mori was performed. Thermal stability of LPA immobilized with silk fibroin is higher than that of free LPA at high temperature judging from the immunoglobulin G (IgG)-binding affinity. However, the apparent value of its affinity decreased relative to that of immobilized WPA. These results indicate that structural information is essential to explore improvement of IgG-binding affinity of immobilized LPA. Therefore, secondary structure of free LPA was detected by its characteristic helical pattern in circular dichroism (CD) in aqueous solution. In addition to this, tertiary fold of four IgG-binding domains were investigated by two-dimensional 1H-NMR spectra. Four significantly high-field shifted cross-peaks attributed to methyl signals of alanine residues suggest that all four domains pack into a three helix bundle motif in solution. These structural data and properties of IgG-binding affinity suggest that spatial arrangement of four IgG-binding domains are packed into a compact globular molecular shape. This causes a certain active site of immobilized LPA to be buried in the silk fibroin fiber.

Stabilization and translation of immobilized mRNA on latex beads for cell-free protein synthesis system

The stability of immobilized mRNA against ribonucleases was investigated in a cell-free protein synthesis system. The plasmid-encoding protein A with the 20-mer poly(A) tail under the control of T7 promoter was constructed, and the corresponding mRNA was synthesized by T7 RNA polymerase reaction. The resulting mRNA was immobilized on oligo(dT)-immobilized latex beads by hybridization utilizing the poly(A) tail of mRNA at the 3'-terminus. The mRNA was stabilized against three types of nucleases (3'-OH exonuclease, 5'-OH exonuclease, and endonuclease) by immobilization. Translation of immobilized mRNA with a continuous-flow cell-free protein-synthesizing system from Saccharomyces cerevisiae was ascertained. Reusability of the immobilized mRNA as genetic information was also examined.

Influence of alkali-treated cornsteep liquor containing medium on protein A production by Staphylococcus aureus

Staphylococcus aureus cultivated in liquid media containing untreated cornsteep liquor (CSL) and alkali-treated CSL produced similar biomass yields (6.5-6.9 g/L). However, contents of protein A in the biomass was 0.5% and 1.56% for untreated CSL and treated CSL, respectively. Addition of treated CSL at 20 g/L achieved optimal enhancement of protein A production (0.11 g/L). Probable factors associated in treated CSL for the enhanced protein A production are discussed.

Characterization of Fv fragments expressed on phage surface

We characterized a phage antibody in which an Fv fragment, namely, a free VH fragment noncovalently associated with a VL fragment that is fused with a truncated cpIII molecule (VL-DeltacpIII), is expressed on the phage surface. D1.3 antibody specific for hen egg-white lysozyme was used as a model system. Both VH and VL-DeltacpIII fragments were stably expressed and associated with each other to form a faithful antigen-binding site. The results of Western blotting indicated that more than 5% of phages expressed the Fv fragment on their surface. Analysis of the kinetics of binding of the phage antibody to the antigen suggested the possibility of presence of phages having multiple-binding sites on a single phage particle.

Overproduction of soluble, extracellular cytotoxin alpha-sarcin in Escherichia coli

The goal of the present study was to establish the condition to obtain preparative amounts of the recombinant cytotoxin alpha-sarcin to be used for immunoconjugate production. alpha-Sarcin cDNA was isolated from Aspergillus giganteus strain MDH 18,894 and its expression in Escherichia coli was attempted by the use of both two-cistron and fusion protein-expression systems. Whereas the former resulted in low intracellular expression level of recombinant alpha-sarcin (r-Sar), the latter allowed high-level expression of the fusion protein in the culture supernatant. A variant form of alpha-sarcin with an additional threonine residue in position 1 (Thr-Sar) was obtained by proteolytic processing of the fusion protein with a final yield after purification of 40 mg/L of culture. Both recombinant proteins r-Sar and Thr-Sar were identical to native a-sarcin with respect to the biochemical properties and to the in vitro biological activity.

[Selected properties of Staphylococcus aureus strains using phenotype to show a lack of coagulase synthesis]

Eighteen of S. aureus strains isolated from clinical specimens and showing negative reaction for coagulase in conventional tube test were characterized by using five different methods: ID32 Staph, API Staph, Gpl-15, STAPH-ZYM (Rosco) and classical tube methods. The membership of all examined strains to S. aureus subsp. aureus was confirmed. None of the strains produced detectable amounts of coagulase but all of them produced protein A and clumping factor. All of them were typable with phages of the III lytic group and 11 of them possessed phage pattern characteristic of the 83A complex. All the investigated hospital strains were resistant to methicillin. Five showed homogenous and 13 heterogenous type of methicillin resistance. Moreover, all of them were resistant to tetracycline, gentamicin, tobramycin and kanamycin and to MLS group of antibiotics.

The efficiency of a cis-cleaving ribozyme in an mRNA coding region is influenced by the translating ribosome in vivo

A cis -cleaving hammerhead ribozyme (Rz) expression system (3A'-Rz) in Escherichia coli has been constructed that can be used to study the involvement of factors that affect ribozyme cleavage in vivo . The ribozyme sequence is placed in the coding region of 3A' mRNA, which is expressed from a semi-synthetic translation assay gene. The size and the 5'-end sequences of the 3' cleavage fragments were determined and the efficiencies of different Rz variants were measured by quantitative primer extension. It is shown that one of the semi-active constructs (3A'-RzIII) can be used as an indicator for ribosomes that read through or terminate at a stop codon upstream of the Rz hammerhead sequence in the mRNA. Readthrough of the stop codon in an uncleaved mRNA gives a full length 3A' protein. Termination at the stop codon upstream of the ribozyme sequence gives a shortened termination product. However, the mRNA fragment that should arise as a result of the auto-cleavage does not give rise to any detectable corresponding truncated protein. Besides studies on translating ribosomes, the 3A'-Rz system can be used to isolate mutant strains that are changed in ribozyme activity either from internal base alterations, or changed interacting host factors.

Pilot scale expression and purification of soluble protein A tagged beta 1,6N-acetylglucosaminyltransferase in CHO cells

Expression of recombinant soluble protein A tagged mouse core 2 beta 6-N-acetylglucosaminyltransferase (E.C. 2.4.1.102) has been scaled-up in CHO cells using a continuously operating fluidized bed system yielding 0.3 U/day. A one step 213 fold purification by affinity chromatography on IgG-Sepharose yielded a stable enzyme preparation with a specific activity of 44 mU/mg. The enzyme was shown to belong to the L-type with a highly restricted specificity for the acceptor substrate Gal beta 1-->3GalNAc alpha 1-->R (core 1). Only little activity towards GlcNAc beta 1-->3Gal-NAc alpha 1-->R (core 3) (< 1%) and no incorporation on unsubstituted benzyl or peptide-bound GalNAc was detected. Zn2+ and to a lesser extent Mn2+ were found to be inhibitory whereas Mg2+ could activate the enzyme. The enzyme preparation proved suitable for in vitro application as a catalyst for the synthesis of core 2 structures.

Regulation of Staphylococcus aureus capsular polysaccharide type 5: CO2 inhibition in vitro and in vivo

Staphylococcus aureus capsular polysaccharide type 5 (CP5) expression was investigated in lung tissue and nasal polyps of two cystic fibrosis (CF) patients, in rats, and in vitro using ELISA and IFA. In CF tissues, S. aureus expressed protein A and teichoic acid but only 1%-5% of cells expressed CP5. When rats were challenged with CP5-positive S. aureus in the granuloma pouch model, only 1%-5% of CP5-positive cells were detectable in pouch exudates. CF and pouch isolates, however, reexpressed CP5 (70%-90% of cells) when grown in vitro with air. Addition of > or = 1% CO2 to air or to O2/N2 gas mixtures reduced CP5 expression significantly (P < .001) in a dose-dependent manner (6%-1% CP5-positive cells). The results show that S. aureus does not produce CP5 in CF airways and in rat granuloma pouches and that CO2 is an environmental signal that regulates CP5 expression.

Variation in the agr-dependent expression of alpha-toxin and protein A among clinical isolates of Staphylococcus aureus from patients with septicaemia

In Staphylococcus aureus synthesis of many virulence factors is regulated by the agr locus. The regulatory molecule RNAIII, induced by agr, activates transcription of the alpha-toxin gene, hla, while it acts as a repressor of the protein A gene, spa. Forty clinical strains of S. aureus from human blood cultures were analysed for alpha-toxin and protein A production. An inverse correlation between alpha-toxin and protein A production was found in most strains. The levels of alpha-toxin and protein A production varied significantly among strains, which indicates various levels of the regulator, RNAIII. This was confirmed by selecting strains producing different amounts of alpha-toxin, showing that the variations in toxin production are due to the variations of RNAIII transcript. However, in one of the selected strains which produced high levels of alpha-toxin, OR153, although RNAIII is also strongly expressed, the specific hla mRNA was unexpectedly low. One partial explanation for the high alpha-toxin production by this clinical isolate might be its lack of extracellular proteases.

Regulation of protein A synthesis by the sar and agr loci of Staphylococcus aureus

The synthesis of protein A in Staphylococcus aureus is regulated by global regulatory loci such as sar and agr. Phenotypic data indicate that both sar and agr suppress protein A synthesis; like agr, sar also regulates protein A production at the transcriptional level. To determine the genetic requirement of sar in protein A suppression, we transformed shuttle plasmids containing various sar fragments into a sar mutant. Our results indicated that the 560-bp sarA transcript, or, more probably, the SarA protein (13.5 kDa), is sufficient for suppressing protein A gene transcription when introduced on a multicopy plasmid or as a single copy in the chromosome. Immunoblot analysis with a chicken anti-protein A antibody also confirmed the reduction in protein A expression in these sar mutant clones. Complementation studies revealed that the transcription of the protein A gene can be suppressed in a sar mutant background by a plasmid containing RNAIII. Surprisingly, in agr deletion mutant clones and in clones derived from the agr-sar double mutant, protein A gene transcription can also be suppressed by plasmids containing the sarA transcript plus additional upstream sequence but not the sarA transcript alone. These data suggest that the sar locus can down-modulate protein A gene transcription via both RNAIII-dependent and RNAIII-independent pathways. Consistent with the hypothesis of an RNAIII-independent pathway is an additional genetic requirement for protein A suppression in the agr deletion mutant RN6911 as well as the isogenic double sar-agr mutant, whereas in the sar mutant background, the sarA transcript encoding the SarA protein alone is sufficient. These data suggested that both sar and agr are coregulators of protein A synthesis in S. aureus.

Detection of protein A produced by Staphylococcus aureus with a fiber-optic-based biosensor

Staphylococcus aureus is a pathogen important in causing human infections and intoxication. A sensitive fiber-optic that produces evanescent waves was developed for the detection of protein A, a product secreted only by S. aureus. In the immunosensor, a 40-mV argon-ion laser that generated laser light at 488 nm was used together with plastic optical fiber and antibodies to protein A were physically adsorbed onto the fiber. The principle of the detection involved a sandwich immunoassay with fluorescein isothiocyanate conjugated with anti-(protein A) immunoglobulin G to produce signals of the antigen-antibody reaction. The detection limit was 1 ng of protein A per milliliter. The fiber-optic immunosensor could be used for rapid and specific detection of S. aureus in clinical specimens and foods.

In vivo expression of exoprotein synthesis with a Sae mutant of Staphylococcus aureus

The expression of exoprotein synthesis of Staphylococcus aureus Sae mutant RC121 and its parental strain was studied under in vivo growth conditions. Cultures of both strains were inoculated into dialysis sacs implanted in sheep peritoneum. Results indicated that similar to in vitro grown mutant cells, Sae mutant RC121 shows diminished synthesis of alpha- and beta-hemolysin, coagulase, DNase and protein A. However, in vitro and in vivo grown mutant cultures showed different exoprotein profiles in SDS-PAGE; some bands from in vivo mutant cultures were diminished or missing and others appeared as more concentrated, when compared with the pattern of the in vivo grown parental strain, while all the exoprotein bands from the in vitro cultures of the mutant were diminished or missing as compared to the in vitro grown parental strain. The virulence of the Sae mutant, assayed by intraperitoneal injection in mice, was lower than that of the parental strain after both in vivo and in vitro growth conditions.

Chaperone-like effect during in vitro refolding of insulin-like growth factor I using a solubilizing fusion partner

A fusion partner, ZZ, derived from staphylococcal protein A, has earlier been shown facilitate the in vitro folding of human insulin-like growth factor I (IGF-I). Although no solubilizing agents were used, there was no problem with precipitation, even at relatively high protein concentrations. We have here investigated this phenomenon further by characterizing the in vitro refolding of IGF-I fused to one or two solubilizing Z domains. The comparison also included IGF-I without a solubilizing fusion partner. Solubility studies of the reduced proteins were performed, in addition to an evaluation of the aggregation occurring during the refolding process. Fusion to one or two Z domains increased the solubility of reduced IGF-I more than 100-fold. In addition, the Z or ZZ fusion partners decreased aggregation of the IGF-I moieties during the renaturation. The fusion partner has an effect resembling that of a cis-acting chaperone during in vitro refolding and may be an alternative to overcome the problems of insolubility and aggregation.

Construction of a fusion protein between protein A and green fluorescent protein and its application to western blotting

Aequorea green fluorescent protein (GFP) and protein A were fused and expressed in Escherichia coli. The fluorescent native fusion protein (PA-GFP) migrated at 47 kDa in SDS-PAGE. However, the non-fluorescent denatured PA-GFP migrated at 57 kDa which corresponds to the theoretical molecular mass. Although the reason(s) for this mobility shift between fluorescent and non-fluorescent molecules remains unclear, the small ring structure within the native molecules may affect their mobility. The cell extract, prepared from an E. coli strain producing PA-GFP, was used in Western and dot blots. The sensitivity and specificity of the PA-GFP detection were sufficient for rapid and easy screening.

High-level production of uniformly ¹⁵N- and ¹³C-enriched fusion proteins in Escherichia coli

An approach to produce 13C- and 15N-enriched proteins is described. The concept is based on intracellular production of the recombinant proteins in Escherichia coli as fusions to an IgG-binding domain, Z, derived from staphylococcal protein A. The production method provides yields of 40-200 mg/l of isotope-enriched fusion proteins in defined minimal media. In addition, the Z fusion partner facilitates the first purification step by IgG affinity chromatography. The production system is applied to isotope enrichment of human insulin-like growth factor II (IGF-II), bovine pancreatic trypsin inhibitor (BPTI), and Z itself. High levels of protein production are achieved in shaker flasks using totally defined minimal medium supplemented with 13C(6)-glucose and (15NH4)2SO4 as the only carbon and nitrogen sources. Growth conditions were optimized to obtain high protein production levels and high levels of isotope incorporation, while minimizing 13C(6)-glucose usage. Incorporation levels of 13C and/or 15N isotopes in purifies IGF-II, BPTI, and Z were confirmed using mass spectrometry and NMR spectroscopy. More than 99% of total isotope enrichment was obtained using a defined isotope-enriched minimal medium. The optimized systems provide reliable, high-level production of isotope-enriched fusion proteins. They can be used to produce 20-40 mg/l of properly folded Z and BPTI proteins. The production system of recombinant BPTI is state-of-the-art and provides the highest known yield of native refolded BPTI.

A novel expression system for Salmonella typhimurium allowing high production levels, product secretion and efficient recovery

A novel expression system for heterologous production in Salmonella typhimurium, taking advantage of the promoter, signal sequence and two IgG-binding domains (ZZ) from staphylococcal protein A, has been investigated. The production of two different fusion proteins, ZZ-M3 and ZZ-M5, was characterized in terms of production levels, product localization (periplasma or culture medium) and product quality after affinity purification. High expression levels and efficient product secretion were obtained, making the system attractive for vaccine development. The potential use of S. typhimurium as host for heterologous production in biotechnology is discussed.

Characterization of the sar locus and its interaction with agr in Staphylococcus aureus

The expression of cell wall and extracellular proteins in Staphylococcus aureus is controlled by global regulatory systems, including sar and agr. We have previously shown that a transposon insertion into the 372-bp sarA gene within the sar locus resulted in decreased expression of several extracellular and cell wall proteins (A. L. Cheung and S. J. Projan, J. Bacteriol. 176:4168-4172, 1994). In this study, Northern (RNA blot) analysis with a 732-bp sarA probe indicated that two major transcripts (0.56 and 1.2 kb) were absent in the sar mutant compared with the parental strain RN6390. Additional transcriptional studies revealed that the sarA gene is encoded within the 0.56-kg transcript. Notably, a plasmid carrying the sarA gene together with a 1.2-kb upstream fragment (1.7 kb total) was able to reestablish the 1.2-kb transcript in the mutant. Although reconstitution of the parental phenotype by the sarA gene was incomplete, the introduction of a plasmid carrying the 1.7-kb fragment to the mutant restored the parental phenotype. Transcription of RNAII and RNAIII, which encode the structural and regulatory genes of agr, respectively, was diminished in the mutant but restored to wild-type levels by complementation with the 1.7-kb fragment. In gel shift assays, cell extracts of this clone were able to retard the mobility of a labeled RNAII promoter probe but not an RNAIII promoter element. These data suggest that sarA and the adjacent upstream DNA are essential to the expression of a DNA-binding protein(s) with specificity for the RNAII promoter, thereby controlling agr-related transcription.

Substrate specificity of beta 1,4-N-acetylgalactosaminyltransferase in vitro and in cDNA-transfected cells. GM2/GD2 synthase efficiently generates asialo-GM2 in certain cells

The substrate specificity of beta 1,4-N-acetylgalactosaminyltransferase has been analyzed using a fusion enzyme which consisted of the catalytic domain of the enzyme and the IgG binding domain of protein A, and also by extracts from cDNA transfectants. Both enzyme sources were capable of producing not only GM2 and GD2, but also asialo-GM2, GalNAc-sialylparagloboside, and Gal-NAc-GD1a from appropriate acceptors, although the efficiencies were at most 1-3% of those of GM2/GD2. The biological significance of these low specificities was studied with transient and stable transfectant cells. From the results of transient expression of the cDNA, asialo-GM2 expression appeared to inversely correlate with GM2 synthase levels in those lines. Consequently, GM2 seemed to be preferentially synthesized when both GM3 and lactosylceramide are available, and asialo-GM2 is synthesized in the absence of GM3 synthesis. However, the results of double immunostaining of CHO transfectants with anti-GM2 and anti-asialo-GM2 antibodies indicated that another factor may be involved in asialo-GM2 synthesis. From the in vitro assay using mixed acceptors, it was concluded that the presence of certain levels of GM2 might enhance the asialo-GM2 synthesis. These results suggest that even acceptors showing low efficiencies in vitro might be used in certain cells depending on the availability of precursors, expression levels of other gangliosides, as well as the kinetic properties of the enzyme, and the compartmentation of the glycosylation machineries in the cells.

Cell surface display of recombinant proteins on Staphylococcus carnosus

A novel expression system for surface display of heterologous proteins on Staphylococcus carnosus cells has been developed. Taking advantage of the promoter and secretion signals, including a propeptide region, from the lipase gene of Staphylococcus hyicus and the cell wall-spanning and membrane-binding region of protein A from Staphylococcus aureus, efficient surface display of an 80-amino-acid peptide from a malaria blood stage antigen could be achieved. A serum albumin binding protein from streptococcal protein G was used both as a general reporter molecule and to increase the accessibility of the surface-displayed proteins. Immunoblotting, immunogold staining, and immunofluorescence on intact recombinant S. carnosus cells verified the presence of the propeptide, the malaria antigen, and the albumin-binding reporter protein on the bacterial surface. For the first time, fluorescence-activated cell sorting was used to analyze the presence of surface-displayed hybrid receptors on gram-positive bacteria.

Construction and characterization of M13 bacteriophages displaying functional IgG-binding domains of staphylococcal protein A

Staphylococcal protein A (SPA) is ranked as a versatile probe in immunoassays because of its immunoglobulin G (IgG)-binding capability. However, poor binding of SPA to the IgG of some laboratory animals and its inability to bind human IgG3 restricts its universal utility. In the present study, DNA encoding the four IgG-binding domains of SPA (E, D, A and B) or the B domain alone has been fused, in separate phagemid vectors, to the 5' end of gene 111 of the phage M13. Upon infection by helper phage M13KO7, phagemid particles encapsulating single-stranded DNA were produced. Dot immunoblot and Western blot analyses showed the presence of fusion proteins on the M13 surface. Binding of rabbit IgG-horseradish peroxidase (IgG-HRP) complex to the phage particles confirmed that the fusion proteins possessed functional IgG-binding domains. The interaction of these phages with immobilised human IgG and its various subclasses was studied by the phage capture immunoassay where the captured phages were detected by a monoclonal antibody to the major coat protein encoded by gene VIII (gVIII). The phages showed maximal binding to IgG1 kappa, followed by IgG2 kappa, and showed negligible binding to the IgG3 kapa and IgG3 lambda subclasses. The specificity of IgG-binding phages was confirmed in a phage capture and elution assay where the binding of these phages to immobilised human IgG1 kapa weas abolished in the presence of excess of soluble protein A. Moreover, IgG-binding phages could be enriched approx. 1000-fold over non-specific phages in a single round of panning.(ABSTRACT TRUNCATED AT 250 WORDS)

Competitive elution of protein A fusion proteins allows specific recovery under mild conditions

A novel system is described for mild elution of fusion proteins by competitive elution. The approach is based on displacement of immobilized fusions containing a monovalent IgG-binding staphylococcal protein A fragment (Z) from an IgG-affinity matrix by a divalent fragment fused to a serum-albumin-binding region derived from streptococcal protein G. Using real-time interaction analysis, the binding (K(aff)) to polyclonal human IgG was found to be 3.3 (+/- 0.4) x 10(8) M-1 for divalent ZZ and 2.0 (+/- 0.1) x 10(7) M-1 for monovalent Z. This more than tenfold difference in binding strength ensures a high efficiency in the elution step. The competitor protein can specifically be removed and recovered from the elution mixture by subsequent passage through a human serum albumin(HSA)-affinity column, leaving only the target fusion protein in the flow-through fraction. Here, we show that a recombinant Klenow fragment of DNA polymerase I expressed in Escherichia coli can be recovered with high yield, and retained activity, from a crude bacterial lysate by IgG-affinity chromatography using mild conditions during both binding and elution.

Artificial antifreeze proteins can improve NaCl tolerance when expressed in E. coli

A chemically synthesized DNA fragment encoding an artificial antifreeze protein was expressed in E. coli as a translational fusion with a truncated protein A. Two constructions were made, with two and four antifreeze domains, respectively. The fusion proteins stimulated the growth of their bacterial host cells at inhibitory NaCl concentrations. The fusion protein carrying four antifreeze domains also conferred improved tolerance towards freezing.

Optical biosensor for monitoring microbial cells

The potential of a new optical biosensor, the resonant mirror, for detecting whole cells is demonstrated. Staphylococcus aureus (Cowan-1) cells, which express protein-A at their surface, were detected by binding to human immunoglobulin G (IgG) immobilized on an aminosilane-derivatized sensor surface at concentrations in the range 8 x 10(6)-8 x 10(7) cells/mL. A control S. aureus strain (Wood-46), which does not express protein-A, gave no significant response. Immobilization of the capture ligand on aminosilane surfaces with and without a hydrogel coating of carboxymethyl-dextran was compared. The greatest binding response was observed with non-dextran-coated surfaces. The sensitivity of the technique was increased a 1000-fold by using a human IgG-colloidal gold conjugate (30 nm) in a sandwich assay format. S. aureus (Cowan-1) cells were detected in spiked milk samples at cell concentrations from 4 x 10(3)-1.6 x 10(6) cells/mL using the sandwich assay.

Expression of a fibrinolytically active human pro-urokinase fusion protein in Escherichia coli

The gene encoding human pro-urokinase(pro-UK) was cloned into plasmid pEZZ318 and fused to the gene coding for the signal peptide of staphylococcal protein A and IgG bindinging domain. The fusion protein which was synthesized under the control of T7 promoter in Escherichia coli and secreted into the growth medium, was found to be fibrinolytically active. Approximately 60% of the total activity was secreted into the culture medium, where levels of activity approached 150,000 I.U./liter and about 40% of the total activity remained in the cell lysate with levels of activity around 100,000 I.U./liter. The fusion protein was purified in a single step by IgG affinity chromatography. These results demonstrate that human pro-UK can be synthesized and secreted by E. coli as a fibrinolytically active fusion protein.

Antigen detection using recombinant, bifunctional single-chain Fv fusion proteins synthesised in Escherichia coli

A gene fusion approach has been used to produce antibody conjugates for use in immunoassays. Escherichia coli expression vectors encoding fusions between the outer membrane protein A signal peptide, an anti-phytochrome single-chain Fv protein, and either Escherichia coli alkaline phosphatase or Staphylococcal protein A downstream of the T7 O10 promoter were constructed. A crude lysate from cells expressing the single-chain Fv-alkaline phosphatase fusion protein could be used directly for the sensitive and specific staining of phytochrome on protein blots by a single-step immunoassay procedure. Following purification by immunoglobulin G affinity chromatography, the Staphylococcal protein A-single-chain Fv fusion protein was also used for selective immunostaining of phytochrome on protein blots by a two-step procedure in which a rabbit immunoglobulin-alkaline phosphatase conjugate was used to detect antigen-bound Staphylococcal protein A. Recombinant antibody conjugates of the types described here are simple and inexpensive to produce and are a realistic alternative to conventional antibody conjugates.

Glycerol monolaurate inhibits the production of beta-lactamase, toxic shock toxin-1, and other staphylococcal exoproteins by interfering with signal transduction

Glycerol monolaurate (GML) is a naturally occurring surfactant that is used widely as an emulsifier in the food and cosmetics industries and is generally regarded as lacking in important biological activities. The recent observation that it inhibits the production of staphylococcal toxic shock toxin-1 (P. M. Schlievert, J. R. Deringer, M. H. Kim, S. J. Projan, and R. P. Novick, Antimicrob. Agents Chemother. 36:626-631, 1992) is therefore rather surprising and raises the interesting question of how such a compound might interact with cells. In this report, we show that GML inhibits the synthesis of most staphylococcal toxins and other exoproteins and that it does so at the level of transcription. We find that GML blocks the induction but not the constitutive synthesis of beta-lactamase, suggesting that it acts by interfering with signal transduction.