Zbasic: A Purification Tag for Selective Ion-Exchange Recovery

A positively charged protein domain, denoted Z_basic, can be used as a general purification tag for purification of recombinantly produced target proteins by cation-exchange chromatography. The Z_basic domain is constructed from the Protein A-derived Z-domain, and engineered to be highly charged, which allows selective capture on a cation exchanger at physiological pH values. Moreover, Z_basic is selective also under denaturing conditions and can be used for purification of proteins solubilized from inclusion bodies. Z_basic can then be used as a flexible linker to the cation-exchanger resin, and thereby allows solid-phase refolding of the target protein.Herein, protocols for purification of soluble Z_basic-tagged fusion proteins , as well as for integrated purification and solid-phase refolding of insoluble fusion proteins , are described. In addition, a procedure for enzymatic tag removal and recovery of native target protein is outlined.

An Orthogonal Fusion Tag for Efficient Protein Purification

In this chapter, we present an efficient method for stringent protein purification facilitated by a dual affinity tag referred to as ABDz1, which is based on a 5 kDa albumin-binding domain from Streptococcal Protein G. The small fusion tag enables an orthogonal affinity purification approach based on two successive and highly specific affinity purification steps. This approach is enabled by native binding of ABDz1 to human serum albumin and engineered binding to Staphylococcal Protein A, respectively. The ABDz1-tag can be fused to either terminus of a protein of interest and the purification steps can be carried out using standard laboratory equipment.

Epidemiology of Staphylococcus aureus in neonates on admission to a Chinese neonatal intensive care unit

Purpose

Little is known about the molecular epidemiology of Staphylococcus aureus in Chinese neonatal intensive care units (NICUs). We describe the molecular epidemiology of S. aureus isolated from neonates on admission to Beijing Children's Hospital.

Methods

From May 2015-March 2016, nasal swabs were obtained on admission from 536 neonates. Cultures were also obtained from body sites with suspected infections. S. aureus isolates were characterized by staphylococcal chromosomal cassette (SCCmec) type, staphylococcal protein A (spa) type, multilocus sequence type (MLST), sasX gene, antimicrobial susceptibility and cytotoxicity. Logistic regression assessed risk factors for colonization.

Results

Overall, 92 (17%) infants were colonized with S. aureus and 20 (3.7%) were diagnosed with culture-positive S. aureus infection. Of the colonized infants, 70% (64/92) harbored methicillin-susceptible S. aureus (MSSA), 30% (28/92) harbored methicillin-resistant S. aureus (MRSA) while 70% (14/20) of infected infants were culture-positive for MRSA, 30% (6/20) were culture-positive for MSSA. Risk factors for colonization included female sex, age 7–28 days, higher birthweight (3270 IQR [2020–3655] grams) and vaginal delivery (p<0.05). The most common MRSA and MSSA clones were community-associated ST59-SCCmecIVa-t437 (60%) and ST188-t189 (15%), respectively. The sasX gene was not detected. Some MSSA isolates (16%) were penicillin-susceptible and some MRSA isolates (18%) were oxacillin-susceptible. MRSA and MSSA had similar cytotoxicity, but colonizing strains were less cytotoxic than strains associated with infections.

Conclusions

S. aureus colonization was common in infants admitted to our NICU and two community-associated clones predominated. Several non-modifiable risk factors for S. aureus colonization were identified. These results suggest that screening infants for S. aureus upon admission and targeting decolonization of high-risk infants and/or those colonized with high-risk clones could be useful to prevent transmission.

Cleaning-in-place of immunoaffinity resins monitored by in situ ATR-FTIR spectroscopy

In the next 10 years, the pharmaceutical industry anticipates that revenue from biotherapeutics will overtake those generated from small drug molecules. Despite effectively treating a range of chronic and life-threatening diseases, the high cost of biotherapeutics limits their use. For biotherapeutic monoclonal antibodies (mAbs), an important production cost is the affinity resin used for protein capture. Cleaning-in-place (CIP) protocols aim to optimise the lifespan of the resin by slowing binding capacity decay. Binding assays can determine resin capacity from the mobile phase, but do not reveal the underlying causes of Protein A ligand degradation. The focus needs to be on the stationary phase to examine the effect of CIP on the resin. To directly determine both the local Protein A ligand concentration and conformation on two Protein A resins, we developed a method based on attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy. ATR-FTIR spectroscopic imaging revealed that applying a carefully controlled load to agarose beads produces an even and reproducible contact with the internal reflection element. This allowed detection and quantification of the binding capacity of the stationary phase. ATR-FTIR spectroscopy also showed that Protein A proteolysis does not seem to occur under typical CIP conditions (below 1 M NaOH). However, our data revealed that concentrations of NaOH above 0.1 M cause significant changes in Protein A conformation. The addition of >0.4 M trehalose during CIP significantly reduced NaOH-induced ligand unfolding observed for one of the two Protein A resins tested. Such insights could help to optimise CIP protocols in order to extend resin lifetime and reduce mAb production costs.

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.

Low plasma basic fibroblast growth factor is associated with laser photocoagulation treatment in adult type 2 diabetes mellitus from the Veterans Affairs Diabetes Trial

Basic fibroblast growth factor (bFGF) is a potent endothelial cell mitogen that does not normally circulate. Yet plasma bFGF-like bioactivity was increased in association with persistent microalbuminuria and retinopathy in adult type 2 diabetes mellitus. In the present study, we tested whether plasma bFGF immunoreactivity (IR) could predict the need for laser treatment of diabetic retinopathy in a baseline subset of advanced type 2 diabetes mellitus from the Veterans Affairs Diabetes Trial (mean: age, 59 years; diabetes duration, 11 years; baseline glycosylated hemoglobin, 9.5%). Plasma bFGF-IR was determined with a sensitive and specific 2-site enzyme-linked immunoassay in 172 patients at the baseline visit. Results were dichotomized at 4.5 pg/mL, the upper limit in healthy men. There was an unexpected significant association between low baseline plasma bFGF-IR level and the interim (4 years) need for laser treatment. First laser treatment was significantly more likely to be required in patients with low compared with high baseline bFGF (19% vs 6%, P = .03 for the difference). After adjusting for clinical risk factors, low vs high bFGF (hazard ratio [HR], 5.01; P = .012), duration of diabetes (HR, 1.05; P = .050), and low-density lipoprotein cholesterol concentration (HR, 0.98; P = .027) were all significantly associated with time to first laser occurrence. These and our prior results suggest that low plasma bFGF-IR may be a marker for the presence of anti-endothelial cell autoantibodies that may contribute to the need for laser photocoagulation treatment in adult men with advanced type 2 diabetes mellitus.

Separation of tricomponent protein mixtures with triblock nanorods

Two-component triblock magnetic nanorods with gold end blocks and nickel interior blocks have been synthesized and used as affinity templates for the simultaneous and efficient separation of a three-component protein mixture. The gold blocks were selectively functionalized with 11-amino-1-undecanethiol, and then glutaraldehyde was used to covalently attach nitrostreptavidin to them. His-tagged proteins bind to the nickel block and biotin-tagged proteins bind to the functionalized gold ends, allowing one to separate a mixture of three proteins with a single material. Each surface-bound protein can be released selectively using imidazole for the His-tagged protein and biotin for the biotinylated protein.

Fabrication of magnetic core@shell Fe oxide@Au nanoparticles for interfacial bioactivity and bio-separation

The immobilization of proteins on gold-coated magnetic nanoparticles and the subsequent recognition of the targeted proteins provide an effective means for the separation of proteins via application of a magnetic filed. A key challenge is the ability to fabricate such nanoparticles with the desired core-shell nanostructure. In this article, we report findings of the fabrication and characterization of gold-coated iron oxide (Fe2O3 and Fe3O4) core@shell nanoparticles (Fe oxide@Au) toward novel functional biomaterials. A hetero-interparticle coalescence strategy has been demonstrated for fabricating Fe oxide@Au nanoparticles that exhibit controllable sizes ranging from 5 to 100 nm and high monodispersity. Composition and surface analyses have proven that the resulting nanoparticles consist of the Fe2O3 core and the Au shell. The magnetically active Fe oxide core and thiolate-active Au shell were shown to be viable for exploiting the Au surface protein-binding reactivity for bioassay and the Fe oxide core magnetism for magnetic bioseparation. These findings are entirely new and could form the basis for fabricating magnetic nanoparticles as biomaterials with tunable size, magnetism, and surface binding properties.

Protein�A immunoadsorption therapy for refractory, mitomycin�C?associated thrombotic microangiopathy

BACKGROUND

Mitomycin C-associated thrombotic microangiopathy (TMA) has a poor prognosis with limited therapeutic options. Most patients die within 4 months of diagnosis due to pulmonary or renal failure. Here, a patient resistant to total plasma exchange (TPE) and immunosuppressive therapy with glucocorticoids, rituximab, vincristine, and splenectomy who was successfully treated with protein A immunoadsorption is described.

CASE REPORT

A 29-year-old woman developed a TMA after chemotherapy with mitomycin C. She presented with thrombocytopenia, pulmonary edema, hemolytic anemia with presence of schistocytes, and renal failure. Immediate TPE (>120 times) and immunosuppressive therapy with glucocorticoids, however, did not improve her clinical situation. Furthermore, she was refractory to subsequent immunosuppressive therapy with rituximab and vincristine and laparoscopic splenectomy. Finally, after 12 cycles of extracorporeal protein A immunoadsorption with a commercially available immunoadsorption system (Immunosorba, Fresenius AG), platelet counts increased with disappearance of hemolytic syndromes.

CONCLUSION

Extracorporeal protein A immunoadsorption with the Immunosorba system emerges as a potentially effective and safe treatment for refractory mitomycin C-associated TMA with only moderate side effects. This therapeutic option may be considered at an early state of the disease to prevent extensive immunosuppression.

Comparison of Two Rapid Tests for Detecting Group A Streptococcal Pharyngitis in the Pediatric Population at Wright-Patterson Air Force Base

This prospective cohort study compared two rapid antigen tests for group A streptococcus in an enrolled pediatric population of a busy Air Force clinic during the autumn of 2005. The study was performed to determine whether the Genzyme test was a more sensitive rapid test than the currently used Quidel test. A highly sensitive rapid test would eliminate the need to perform backup cultures, thus saving time and facilitating faster diagnosis and treatment. The study revealed that the Genzyme test was more sensitive (85.5%) than the Quidel test (79.5%). However, the difference was not statistically significant using the McNemar chi(2) tool and was attributable to random variability. Therefore, future comparative studies need to be performed to find a rapid antigen test with sensitivity comparable to that of throat culture, for use at the Wright-Patterson Air Force Base pediatric clinic.

Construction of a novel synergistic system for production and recovery of secreted recombinant proteins by the cell surface engineering

We determined whether the cocultivation of yeast cells displaying a ZZ-domain and secreting an Fc fusion protein can be a novel tool for the recovery of secreted recombinant proteins. The ZZ-domain from Staphylococcus aureus protein A was displayed on the cell surface of Saccharomyces cerevisiae under the control of the GAL1 promoter. Strain S. cerevisiae BY4742 cells displaying the ZZ-domain on their surface were used for cocultivation with cells that produce a target protein fused to the Fc fragment as an affinity tag. The enhanced green fluorescent protein or Rhizopus oryzae lipase was genetically fused to the N and C termini of the Fc fragment of human immunoglobulin G, respectively. Through analysis by fluorescence-activated cell sorting and enzymatic assay, it was demonstrated that these fusion proteins are successfully produced in the medium and recovered by affinity binding with the cell surface displaying the ZZ-domain. These results suggest that the ZZ-domain-displaying cell and Fc fusion protein-secreting cell can be applied to use in synergistic process of production and recovery of secreted recombinant proteins.

A New Approach for the Detection and Identification of Protein Impurities Using Combinatorial Solid Phase Ligand Libraries

We propose a novel method for detection of protein impurities present in plasma-derived and recombinant purified injectable biopharmaceuticals by enhancing the concentration of protein impurities, in essence "amplifying" their presence to detectable levels. The method is based on the capture of proteins using a combinatorial solid-phase hexapeptides ligand library previously described for the reduction of protein concentration difference in biological fluids. Three proteins have been investigated: Staphylococcus aureus Protein A, expressed in Escherichia coli and supplied as 99% pure, recombinant human albumin, expressed in Pichia pastoris and certified as 95% pure, and therapeutic albumin supplied as 96-98% pure injectable solution. In all cases, after treatment with the ligand libraries, a number of additional polypeptide chains, not visible in the control, could be detected and obtained in sufficient amounts for MS analysis. In the cases of the two recombinant proteins, it could be demonstrated that a number of these polypeptide chains were host cell proteins still present in the purified product. In addition, a substantial number of these spots were found to be cleavage products of the original recombinant DNA species. Such cleavage products were particularly abundant in the recombinant human albumin preparation. From pure injectable serum albumin, a number of human plasma protein impurities were also identified by LC-MS/MS analysis. Treatment with ligand libraries of purified proteins is thus seen as a very powerful method of capture and concentration of host proteins and cleaved products for further analysis to control better the quality of industrial biotechnology products.

Affinity chromatography matures as bioinformatic and combinatorial tools develop

Affinity chromatography has the reputation of a more expensive and less robust than other types of liquid chromatography. Furthermore, the technique is considered to stand a modest chance of large-scale purification of proteinaceous pharmaceuticals. This perception is changing because of the pressure for quality protein therapeutics, and the realization that higher returns can be expected when ensuring fewer purification steps and increased product recovery. These developments necessitated a rethinking of the protein purification processes and restored the interest for affinity chromatography. This liquid chromatography technique is designed to offer high specificity, being able to safely guide protein manufactures to successfully cope with the aforementioned challenges. Affinity ligands are distinguished into synthetic and biological. These can be generated by rational design or selected from ligand libraries. Synthetic ligands are generated by three methods. The rational method features the functional approach and the structural template approach. The combinatorial method relies on the selection of ligands from a library of synthetic ligands synthesized randomly. The combined method employs both methods, that is, the ligand is selected from an intentionally biased library based on a rationally designed ligand. Biological ligands are selected by employing high-throughput biological techniques, e.g. phage- and ribosome-display for peptide and microprotein ligands, in addition to SELEX for oligonucleotide ligands. Synthetic mimodyes and chimaeric dye-ligands are usually designed by rational approaches and comprise a chloro-triazinlyl scaffold. The latter substituted with various amino acids, carbocyclic, and heterocyclic groups, generates libraries from which synthetic ligands can be selected. A 'lead' compound may help to generating a 'focused' or 'biased' library. This can be designed by various approaches, e.g.: (i) using a natural ligand-protein complex as a template; (ii) applying the principle of complementarity to exposed residues of the protein structure; and (iii) mimicking directly a natural biological recognition interaction. Affinity ligands, based on the peptide structure, can be peptides, peptide-mimetic derivatives (<30 monomers) and microproteins (e.g. 25-200 monomers). Microprotein ligands are selected from biological libraries constructed of variegated protein domains, e.g. minibody, Kunitz, tendamist, cellulose-binding domain, scFv, Cytb562, zinc-finger, SpA-analogue (Z-domain).

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).

Fast on-column protein digestion with subsequent peptide mapping using tandem mass spectrometry with information dependent acquisition

A platform for rapid on-line protein digestion of protein mixtures for direct infusion to a mass spectrometer is presented. A mixture of protein A, staphylococcal enterotoxin B and cytochrome c was used as a model mixture injected on a gel filtration column and a trypsin reactor which were connected in series to a micro liquid chromatography (microLC) system. The peptides in the column eluate were analyzed with ESI tandem mass spectrometry, utilizing information dependent acquisition (IDA). In one step, the proteins in the mixture (microM concentrations) were concomitantly desalted, separated, digested and identified with an overall analysis time of less than 40 min. Protein sequence coverage of 78-95% for the involved substances was achieved.

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 - a new ligand for human C-reactive protein

Phosphorylcholine (PC) is a classical ligand of C-reactive protein (CRP), a clinically important acute phase protein. In search of new ligands, CRPs were affinity-purified from several pathological samples, which exhibited distinct molecular variants induced in different diseases. Both glycosylated and non-glycosylated CRPs showed calcium-independent differential-binding to Staphylococcus aureus cell-surface Protein A. CRP possesses separate binding sites for Protein A and PC with different binding constants. We have demonstrated that Protein A is another ligand in addition to PC establishing an extended definition of CRP. Protein A binding may impart immunomodulatory roles of CRP in combating microorganisms or other foreign materials.

Use and Optimization of a Dual-Flowrate Loading Strategy To Maximize Throughput in Protein-A Affinity Chromatography

The effect of an alternate strategy employing two different flowrates during loading was explored as a means of increasing system productivity in Protein-A chromatography. The effect of such a loading strategy was evaluated using a chromatographic model that was able to accurately predict experimental breakthrough curves for this Protein-A system. A gradient-based optimization routine is carried out to establish the optimal loading conditions (initial and final flowrates and switching time). The two-step loading strategy (using a higher flowrate during the initial stages followed by a lower flowrate) was evaluated for an Fc-fusion protein and was found to result in significant improvements in process throughput. In an extension of this optimization routine, dynamic loading capacity and productivity were simultaneously optimized using a weighted objective function, and this result was compared to that obtained with the single flowrate. Again, the dual-flowrate strategy was found to be superior.

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.

Characterization of protein variants and post-translational modifications: ESI-MSn analyses of intact proteins eluted from polyacrylamide gels

We have developed a strategy to characterize protein isoforms, resulting from single-point mutations and post-translational modifications. This strategy is based on polyacrylamide gel electrophoresis separation of protein isoforms, mass spectrometry (MS) and MSn analyses of intact proteins, and tandem MS analyses of proteolytic peptides. We extracted protein isoforms from polyacrylamide gels by passive elution using SDS, followed by nanoscale hydrophilic phase chromatography for SDS removal. We performed electrospray ionization MS analyses of the intact proteins to determine their molecular mass, allowing us to draw hypotheses on the nature of the modification. In the case of labile post-translational modifications, like phosphorylations and glycosylations, we conducted electrospray ionization MSn analyses of the intact proteins to confirm their presence. Finally, after digestion of the proteins in solution, we performed tandem MS analyses of the modified peptides to locate the modifications. Using this strategy, we have determined the molecular mass of 5-10 pmol of a protein up to circa 50 kDa loaded on a gel with a 0.01% mass accuracy. The efficiency of this approach for the characterization of protein variants and post-translational modifications is illustrated with the study of a mixture of kappa-casein isoforms, for which we were able to identify the two major variants and their phosphorylation site and glycosylation motif. We believe that this strategy, which combines two-dimensional gel electrophoresis and mass spectrometric analyses of gel-eluted intact proteins using a benchtop ion trap mass spectrometer, represents a promising approach in proteomics.

SwellGel: a sample preparation affinity chromatography technology for high throughput proteomic applications

Development of high throughput systems for purification and analysis of proteins is essential for the success of today's proteomic research. We have developed an affinity chromatography technology that allows the customization of high capacity/high throughput chromatographic separation of proteins. This technology utilizes selected chromatography media that are dehydrated to form uniform SwellGel discs. Unlike wet resin slurries, these discs are easily adaptable to a variety of custom formats, eliminating problems associated with resin dispensing, equilibration, or leakage. Discs can be made in assorted sizes (resin volume 15 microl-3 ml) dispensed in various formats (384-, 96-, 48-, and 24-well microplates or columns) and different ligands can be attached to the matrix. SwellGel discs rapidly hydrate upon addition of either water or the protein sample, providing dramatically increased capacity compared to coated plates. At the same time, the discs offer greater stability, reproducibility, and ease of handling than standard wet chromatography resins. We previously reported the development of SwellGel for the purification of 6x His- and glutathione-S-transferase (GST)-tagged fusion proteins [Prot. Exp. Purif. 22 (2001) 359-366]. In this paper, we discuss an expanded list of SwellGel stabilized chromatographic methods that have been adapted to high throughput formats for processing protein samples ranging from 10 microl to 10 ml (1 microg to 50 mg protein). Data are presented applying SwellGel discs to high throughput proteomic applications such as affinity tag purification, protein desalting, the removal of abundant proteins from serum including albumin and immunoglobulin, and the isolation of phosphorylated peptides for mass spectrometry.

Immunoadsorption inferior to plasma exchange in a patient with chronic inflammatory demyelinating polyradiculoneuropathy

Staphylococcal protein A immunoadsorption and plasma exchange were compared for treating chronic inflammatory demyelinating polyradiculoneuropathy. In a single patient, plasma exchange had a more beneficial effect than immunoadsorption on clinical outcome measures. Serum IgM antibody activity to peripheral nerve fell significantly following plasma exchange. Serum IgM and IgA fell more and IgG less after plasma exchange than after immunoadsorption. The superior efficacy of plasma exchange to immunoadsorption in this case may have been the result of removal of an IgM antibody.

On-line microdialysis of proteins with high-salt buffers for direct coupling of electrospray ionization mass spectrometry and liquid chromatography

Mass spectrometry (MS) is one of the most powerful instrumental techniques for protein analysis. The electrospray ionization (ESI) approach is known to be very gentle and at the same time compatible with liquid separation techniques such as HPLC and CE. However, ESI is known to be susceptible to salts and impurities, which often cause a dramatic decrease in sensitivity due to the suppression of the ionization of the product of interest. For this reason, LC-ESI-MS coupling has so far been largely limited to reversed-phase chromatography with its hydro-organic mobile phases. Other chromatographic techniques are typically "linked" to ESI-MS by time consuming, off-line desalting steps. On-line microdialysis has been proposed as a solution to this dilemma. In this paper, we introduce an improved microdialysis system, which enlarges the number of putative applications, thus allowing chromatographic separations of biological compounds to be directly coupled to MS detection with little to no loss in time or chromatographic resolution. Examples include separations by affinity, ion-exchange and size-exclusion chromatography, all of which were connected successfully to the ESI-MS detector via the on-line microdialyzer. We propose that, using this system, any kind of chromatography technique can be coupled to ESI-MS, thus enabling for example application in quality control or process monitoring of many bioproduction and downstream processes.

Applications of novel affinity cassette methods: use of peptide fusion handles for the purification of recombinant proteins

In this article, recent progress related to the use of different types of polypeptide fusion handles or 'tags' for the purification of recombinant proteins are critically discussed. In addition, novel aspects of the molecular cassette concept are elaborated, together with areas of potential application of these fundamental principles in molecular recognition. As evident from this review, the use of these concepts provides a powerful strategy for the high throughput isolation and purification of recombinant proteins and their derived domains, generated from functional genomic or zeomic studies, as part of the bioprocess technology leading to their commercial development, and in the study of molecular recognition phenomena per se. In addition, similar concepts can be exploited for high sensitivity analysis and detection, for the characterisation of protein bait/prey interactions at the molecular level, and for the immobilisation and directed orientation of proteins for use as biocatalysts/biosensors.

Identification of model peptides as affinity ligands for the purification of humanized monoclonal antibodies by means of phage display

A proof-of-principle study was initiated to determine whether phage-display technology could be used to identify peptides as leads in the customization of ligands for affinity chromatography and to identify a peptide or peptidomimetic for use as a Protein A alternative in the affinity purification of monoclonal antibodies. The constant region of humanized anti-Tac (HAT), prepared by pepsin digestion and receptor-affinity chromatography, was used as the target for phage display in this study. As such, 20 phage-derived peptide sequences were identified from four rounds of biopanning with two linear phage-display libraries (7-mer, containing 100 copies of 2 x 10(9) sequences and 12-mer, containing 70 copies of 1.4 x 10(9) sequences). Five peptides were synthesized for use as affinity ligands, based on sequence homology to Protein A, sequence redundancy, and amino acid motifs. The best HAT binding immobilized peptide was EPIHRSTLTALL. The best-fit analysis of this peptide sequence with Protein A yielded an alignment well within the Fc binding domain of Protein A. These results suggest that phage display can serve as a tool in the identification of peptides as model ligands for affinity chromatography.

[Effect of staphylococcus active substances on ATPase activity of smooth muscle actomyosin and myosin]

The effect of staphylococcus active substances--protein A (PA) and peptidoglican (PG) at concentrations 10(-6)-10(-2) mg/ml on the ATPase activity of pig stomach natural actomyosin and myosin was studied. It was shown that PA and PG at direct contact with smooth muscle contractile proteins caused the activation and inhibition of ATPase activity, respectively. On the basis of this investigation it was assumed that staphylococcal active substances were able to modify of the ATPase activity smooth muscle contractile proteins perhaps via direct action on the myosin molecule, which could be accompanied by conformational changes of the active center of myosin ATPase.

Expression, purification and applications of staphylococcal protein A fused to cellulose-binding domain

Because staphylococcal Protein A (ProtA) binds specifically to IgG, it has been used for many immunological manipulations, most notably antibody purification and diagnostics. Immobilization is required for most of these applications. Here we describe a genetic-engineering approach to immobilizing ProtA on cellulose, by fusing it to cellulose-binding domain (CBD) derived from the cellulose-binding Protein A of Clostridium cellulovorans. The bifunctional fusion protein was expressed in Escherichia coli, recovered on a cellulose column and purified by elution at alkaline pH. ProtA-CBD was used to purify IgG from rabbit serum and its ability to bind IgG from different sources was determined. The bifunctional chimaeric protein can bind up to 23.4 mg/ml human IgG at a ratio of 1 mol of ProtA-CBD/2 mol of human IgG, and can purify up to 11.6 mg/ml rabbit IgG from a serum. The ability to bind functionally active CBD-affinity reagents to cellulosic microtitre plates was demonstrated. Our results indicate that a combination of CBD-affinity reagents and cellulosic microtitre plates is an attractive diagnostics matrix for the following reasons: (i) cellulose exhibits very low non-specific binding; and (ii) CBD-fusion proteins bind directly to cellulose at high density. A unique signal-amplification method was developed based on the ability of ProtA-CBD to link stained cellulose particles to primary antibody in a Western blot.

Protein engineering of an IgG-binding domain allows milder elution conditions during affinity chromatography

One of the problems in the recovery of antibodies by affinity chromatography is the low pH, which is normally essential to elute the bound material from the column. Here, we have addressed this problem by constructing destabilized mutants of a domain analogue (domain Z) from an IgG-binding bacterial receptor, protein A. In order to destabilize the IgG-binding domain, two protein engineered variants were constructed using site-directed mutagenesis of the second loop of this antiparallel three-helix bundle domain. In the first mutant (Z6G), the second loop was extended with six glycines in order to evaluate the significance of the loop length. In the second mutant (ZL4G), the original loop sequence was exchanged for glycines in order to evaluate the importance of the loop forming residues. Both mutated variants have a lower alpha-helical content, as well as a lower thermal and chemical stability compared to the parent Z-molecule. The affinity to IgG was slightly lowered in both cases, mainly due to higher dissociation rates. Interestingly, the elution studies showed that most of the bound IgG-molecules could be eluted at a pH as high as 4.5 from columns with the engineered ligands, while only 70% of the bound IgG could be eluted from the matrix with the parent Z as ligand.

Staphylococcus aureus isolated from Kawasaki disease patients hyper-releases extracellular protein A

S. aureus isolates from patients with Kawasaki disease (KD) release high levels of extracellular protein A (SpA), as compared to S. aureus in other diseases. The molecular weight of this released protein A is about 70 kDa. Extracellular KD SpA purified by affinity chromatography possessed the same amino acid sequence at the NH2-terminal IgG binding region and the same antigenic specificity as recombinant and cell-wall-bound SpA preparations. The size of DNA fragments containing the spa gene from S. aureus KD strains was 160-165 kb. All of these DNA fragments contained the igb portion encoding the IgG-binding region of KD SpA. Significantly higher molecular size of the SpA molecules hyper-released in the stationary-phase culture and the lack of production of other exo-proteins allow us to speculate that S. aureus isolated from patients with KD have mutations occurring in the agr locus.

Aqueous two-phase systems containing self-associating block copolymers. Partitioning of hydrophilic and hydrophobic biomolecules

A series of proteins and one membrane-bound peptide have been partitioned in aqueous two-phase systems consisting of micelle-forming block copolymers from the family of Pluronic block copolymers as one polymer component and dextran T500 as the other component. The Pluronic molecule is a triblock copolymer of the type PEO-PPO-PEO, where PEO and PPO are poly(ethylene oxide) and poly(propylene oxide), respectively. Two different Pluronic copolymers were used, P105 and F68, and the phase diagrams were determined at 30 degrees C for these polymer systems. Since the temperature is an important parameter in Pluronic systems (the block copolymers form micellar-like aggregates at higher temperatures) the partitioning experiments were performed at 5 and 30 degrees C, to explore the effect of temperature-triggered micellization on the partitioning behaviour. The temperatures correspond to the unimeric (single Pluronic chain) and the micellar states of the P105 polymer at the concentrations used. The degree of micellization in the F68 system was lower than that in the P105 system, as revealed by the phase behaviour. A membrane-bound peptide, gramicidin D, and five different proteins were partitioned in the above systems. The proteins were lysozyme, bovine serum albumin, cytochrome c, bacteriorhodopsin and the engineered B domain of staphylococcal protein A, named Z. The Z domain was modified with tryptophan-rich peptide chains in the C-terminal end. It was found that effects of salt dominated over the temperature effect for the water-soluble proteins lysozyme, bovine serum albumin and cytochrome c. A strong temperature effect was observed in the partitioning of the integral membrane protein bacteriorhodopsin, where partitioning towards the more hydrophobic Pluronic phase was higher at 30 degrees C than at 5 degrees C. The membrane-bound peptide gramicidin D partitioned exclusively to the Pluronic phase at both temperatures. The following trends were observed in the partitioning of the Z protein. (i) At the higher temperature, insertion of tryptophan-rich peptides increased the partitioning to the Pluronic phase. (ii) At the lower temperature, lower values of K were observed for ZT2 than for ZT1.

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.

Characterization of intermediates in the process of plant peroxisomal protein import

A hybrid protein in which the immunoglobulin G-binding domain of Staphylococcus aureus protein A replaced the N-terminal 43 amino acids of glycolate oxidase (a peroxisomal protein) was affinity purified after expression in Escherichia coli and used to study peroxisomal protein import in vitro. The fusion protein, which co-purifies with the bacterial chaperones dnaK and groEL, binds to glyoxysomes and is partially translocated in an ATP-dependent reaction which is independent of eukaryotic cytosol. Both binding and translocation are dependent upon the amount of glyoxysomes present. The partially translocated species has a transmembrane location and is extractable by salt, indicating that it is held in the membrane by ionic interactions. In the absence of ATP, the fusion protein binds to the surface of the glyoxysomes and competes the binding of authentic matrix proteins. The surface-bound protein can be chased to the transmembrane species upon the addition of ATP. These results indicate that the surface-bound form is a true translocation intermediate. The availability of this fusion protein in milligram quantities offers the possibility to use the intermediate formed in the absence of ATP and the transmembrane species to probe interactions with the peroxisome import machinery.

Sarcosine reductase of Tissierella creatinophila: purification and characterization of its components

Sarcosine reductase is the only reductase system present in Tissierella creatinophila when grown on creatinine plus formate. The acetyl-phosphate-forming component protein C was purified to homogeneity. SDS-PAGE of the purified protein revealed two protein bands with apparent mol. masses of 62 and 50 kDa. The N-terminal amino acid sequence of the two subunits was determined. Antibodies raised against each of the subunits of protein C from Eubacterium acidaminophilum cross-reacted with the corresponding protein present in T. creatinophila, Clostridium litorale and Clostridium sporogenes. The arsenate-dependent hydrolysis of acetyl phosphate catalyzed by protein C was partly inhibited by antibodies directed against the large subunit. Antibodies raised against the small subunit were twice as effective, which indicates that this subunit is the primary site of acetyl transfer from acetyl phosphate. The protein A component of the sarcosine reductase of T. creatinophila was purified to homogeneity by cochromatography with thioredoxin reductase on DEAE-Sephacel, hydroxylapatite, Q-Sepharose, and Sephacryl 100-HR. Protein A had an apparent mol. mass of 21 kDa. Its N-terminal amino acid sequence showed high similarities to that of other proteins A. Initial steps for the purification and preliminary characterization of the sarcosine-specific, substrate-binding protein Bsarcosine component of T. creatinophila indicated the involvement of a 50-kDa protein.

Detection and analysis of Staphylococcal enterotoxin A in food by Western immunoblotting

Western blotting has the potential to overcome some of the major problems associated with enzyme-linked immunosorbent assay (ELISA) detection of toxins in food, such as cross-reactivity with unrelated antigens and insensitivity with heat-treated foods, because the Western procedure solubilizes denatured protein and allows characterization of the antigen that reacts with the antibody. A simple Western immunoblotting protocol was developed to identify and measure the level of Staphylococcus aureus enterotoxin A (SEA) in food. Test samples are merely homogenized with no additional solubilization or pretreatment steps. The immunoblots detect SEA at levels as low as 100 pg/ml. Using the simplified sample preparation, both native and heat-denatured SEA were identified in a variety of foods including mushrooms, milk, potato salad and meat products. Our data suggest that SEA is being secreted at mid-log growth in BHI media as well as in mushrooms. These results suggest that Western blotting is a useful tool for determining the presence of SEA in foods because it allows characterization of the antigen reacting with the antibody and can be used for heat-treated foods, thus overcoming some of the limitations of the ELISA test.

Accelerated recombinant protein purification process development automated, robotics-based integration of chromatographic purification and analysis

Recovery of recombinant proteins from endogenous, host molecules can be an experimentally intensive and time-consuming task. Often the time to analyze material during development of recovery procedures is the rate-limiting step. Nowadays, modern techniques and equipment are being specifically engineered to make this effort much more efficient. We present a case study to illustrate how a new, automation tool, designed for easy, systematic methods development, can be used for very rapid process and analytical optimization. This tool uses robotics to integrate process development with rapid LC-based analysis requiring no user intervention. The methods and procedures described can be generalized to any recombinant protein recovery campaign.

Protein A-immunoadsorption in chemotherapy associated hemolytic-uremic syndrome

Circulating IgG-immune complexes (IgG-IC) play a role in the complex etiology of C-HUS. In an ongoing open clinical study protein A immunoadsorption treatment is carried out for patients who developed severe forms of the syndrome after mitomycin-C chemotherapy. So far, successful treatment of 14 out of 19 evaluable patients was possible. A protein A immunoadsorption system was used, allowing processing of large plasma volumes to eliminate IgG and IgG-IC from the patient's plasma.

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.

Selective adsorption: a new method for purification of protein A-gold complexes

Protein gold complexes are prepared by adding gold colloids to cytochemically active proteins in solution. The gold particles of the colloid form complexes with the protein spontaneously, but some of the protein remains uncomplexed. Currently, when protein A-gold complexes are prepared, the uncomplexed protein. A is separated from the complex by ultracentrifugation, which is a lengthy procedure and requires special equipment. This report describes a simple and rapid method for removing uncomplexed protein A from freshly-prepared "crude" protein A-gold at the laboratory bench. In this method, larger gold particles of 15-nm diameter are added to a crude protein A-gold preparation made with smaller particles (e.g.,6nm diameter). The 15-nm particles adsorb uncomplexed protein A preferentially, but do not form complexes with already-formed 6-nm protein A-gold. The adsorbed protein A, attached to the 15-nm particles, can then be sedimented in a bench centrifuge, leaving the purified 6-nm protein A-gold complexes in the supernatant. The stability, immunocytochemical activity, and degree of aggregation of the protein A-gold complexes prepared by this method are comparable to protein A-gold complexes prepared by ultracentrifugation. The method is simple to perform, avoids lengthy purification procedures, and yields complexes with reproducible labelling characteristics.

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.

Affinity chromatography of recombinant peptides/proteins based on a calmodulin fusion tail

An affinity chromatography system has been developed for the separation of recombinant fusion proteins based on the Ca(2+)-dependent binding of calmodulin (CaM) to the drug phenothiazine. Specifically, in the presence of Ca2+, a recognition site for phenothiazine is exposed on calmodulin, allowing the binding of this drug to CaM. Upon removal of Ca2+ with EGTA, the conformation of calmodulin changes, and the phenothiazine--CaM complex dissociates. This Ca(2+)-dependent binding has been exploited in the development of a fusion tail approach for the affinity purification of recombinant proteins and peptides. Protein A (ProtA) was employed as a model protein to demonstrate the advantages of this approach. In particular, the developed affinity chromatography system was used to isolate several ProtA--CaM fusion proteins. These recombinant fusion proteins were expressed in Escherichia coli and Saccharomyces cerevisiae from appropriately designed plasmids. Four different plasmids (two each for the bacteria and yeast) were used that encoded the fusion of CaM to the immunoglobulin-binding portion of protein A. After expression of the fusion protein, the crude cell lysates were loaded onto the phenothiazine affinity column in the presence of a Ca(2+)-containing buffer. Upon elution with an EGTA buffer, the ProtA--CaM fusion protein was purified, as confirmed by SDS-PAGE electrophoresis and Western blot analysis.

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 murine brain-reactive monoclonal IgG autoantibodies

A diversity of brain-reactive autoantibodies (BRAA) is found in the sera and cerebrospinal fluid in elevated amounts in systemic lupus erythematosus (SLE) and correlates with some CNS manifestations of both human and murine SLE. In order to test the hypothesis that BRAA mediate the CNA manifestations, we are developing a library of brain-reactive monoclonal autoantibodies (BRMA) from autoimmune mice for characterization. We have recently reported on the production of BRMA of the IgM class from unimmunized autoimmune mice. In the current study we extend our investigations and report on the production and characterization of two BRMA of the IgG class. These antibodies react against integral brain membrane antigens of approximately 58, 32, and 30 kDa by immunoblot. Reactivity to such antigens is also found in a majority of the autoimmune murine serum samples tested, but not in nonautoimmune mice. These IgG BRMA show reactivity to cell bodies of the cerebral cortex, hippocampus, and hypothalamus of murine brain but not to fiber tracts. They also react with an integral thymus membrane antigen, but not to antigens of other tissues tested. Because of their properties, BRMA such as those characterized here are likely to be of pathogenic significance in CNS involvement in SLE.

DNA clearance in chromatography of proteins, exemplified by affinity chromatography

Complications of DNA clearance in protein chromatography using the conventional methodology of spiking experiments are reported. Protein A affinity chromatography demonstrated this complications in a small scale experiment. A concentrated hybridoma culture supernatant was spiked with DNA extracted from hybridoma cells fed with [3H]thymidine. Protein A affinity chromatography was subsequently carried out. The column effluent was collected in fractions, and each fraction was analyzed for radioactivity and IgG levels. A substantial amount of DNA was eluted before the main IgG peak. Frequently a small peak is observed in front of the main peak in protein chromatography. This phenomenon can be explained by either displacement effects, or incomplete washing, or hysteresis during the adsorption and desorption conditions. Fractionation at the beginning of elution is critical to the maintenance of a high standard protein purity.

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.

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.