Electrophoretic transfer of proteins across polyacrylamide membranes

Hollow microgel based ultrathin thermoresponsive membranes for separation, synthesis, and catalytic applications

Thermoresponsive core-shell microgels with degradable core are synthesized via surfactant based free radical polymerization using N,N'-(1,2-dihydroxy-ethylene)bis(acrylamide) (DHEA) as a cross-linker for core preparation. The 1,2-glycol bond present in DHEA is susceptible to NaIO4 solution, and thus, the structure can be cleaved off resulting in hollow microgel. Ultrathin membranes are prepared by suction filtration of a dilute suspension of core-shell microgels over a sacrificial layer of Cd(OH)2 nanostrand coated on track etched membrane. After removal of the degraded cores from microgels, the membranes are cross-linked with glutaraldehyde and the nanostrands are removed by passing a 10 mM HCl solution. The prepared membranes are thoroughly characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and dynamic contact angle for morphology, thermoresponsive, and hydrophilic properties, respectively. The prepared membranes showed thermoresponsive permeation behavior and remarkable separation performance for low molecular weight dyes and lysozyme protein. These membranes are also used to synthesize gold nanoparticles and immobilize lactate dehydrogenase enzyme for catalytic and biocatalytic application. The results for water permeation, solute rejection, and ability to immobilize gold nanoparticles and enzymes showed its wide range of applicability. Furthermore, the synthesis of hollow microgel is simple and environmentally friendly, and the membrane preparation is easy, scalable, and other microgel systems can also be used. These responsive membranes constitute a significant contribution to advanced separation technology.

Proteomic analysis of colorectal cancer: discovering novel biomarkers

Colorectal cancer is one of the most common cancers in the Western world. When detected at an early stage, the majority of cancers can be cured with current treatment modalities. However, most cancers present at an intermediate stage. The discovery of sensitive and specific biomarkers has the potential to improve preclinical diagnosis of primary and recurrent colorectal cancer, and holds the promise of prognostic and therapeutic application. Current biomarkers such as carcinoembryonic antigen lack sensitivity and specificity for general population screening. This review aims to highlight the role of current proteomic technologies in the discovery and validation of potential biomarkers with a view to translation to the clinic.

Ultradepletion of human plasma using chicken antibodies: a proof of concept study

Human plasma arguably represents the most comprehensive version of the human proteome. Despite its immense theoretical discovery potential, plasma has many high and medium abundance proteins that mask low abundance protein disease biomarkers of relevance, making the discovery of novel diagnostic markers particularly difficult. Some form of protein depletion and/or fractionation is essential in order to detect markers of low abundance. Here, we describe a "proof of concept" two-pronged approach to immunodeplete abundant proteins from human plasma. The method, called API (Abundant Protein Immunodepletion), involves the fractionation of plasma using dual ion exchange columns (protein repetitive orthogonal offline fractionation (PROOF)) to simplify the proteome, the production of polyclonal IgY against each fraction and finally using the purified antibodies in a immunodepletion column. We explored the use of this product for immunodepletion of human plasma and identified a total of 165 nonredundant proteins after depletion. Of these, 38 proteins that were not previously identified in nondepleted plasma were now detected. It is envisaged that further optimization of the method as well as its cyclic implementation (by reinjecting depleted plasma into chickens for second round of antibody production) can make this technology highly robust, extremely cost-effective, and ideal for high throughput biomarker discovery.

Sample preparation and fractionation for proteome analysis and cancer biomarker discovery by mass spectrometry

Sample preparation and fractionation technologies are one of the most crucial processes in proteomic analysis and biomarker discovery in solubilized samples. Chromatographic or electrophoretic proteomic technologies are also available for separation of cellular protein components. There are, however, considerable limitations in currently available proteomic technologies as none of them allows for the analysis of the entire proteome in a simple step because of the large number of peptides, and because of the wide concentration dynamic range of the proteome in clinical blood samples. The results of any undertaken experiment depend on the condition of the starting material. Therefore, proper experimental design and pertinent sample preparation is essential to obtain meaningful results, particularly in comparative clinical proteomics in which one is looking for minor differences between experimental (diseased) and control (nondiseased) samples. This review discusses problems associated with general and specialized strategies of sample preparation and fractionation, dealing with samples that are solution or suspension, in a frozen tissue state, or formalin-preserved tissue archival samples, and illustrates how sample processing might influence detection with mass spectrometric techniques. Strategies that dramatically improve the potential for cancer biomarker discovery in minimally invasive, blood-collected human samples are also presented.

Membrane-based techniques for the separation and purification of proteins: an overview

Membrane processes are increasingly reported for various applications in both upstream and downstream technology, such as microfiltration, ultrafiltration, emerging processes as membrane chromatography, high performance tangential flow filtration and electrophoretic membrane contactor. Membrane-based processes are playing critical role in the field of separation/purification of biotechnological products. Membranes became an integral part of biotechnology and improvements in membrane technology are now focused on high resolution of bioproduct. In bioseparation, applications of membrane technologies include protein production/purification, protein-virus separation. This manuscript provides an overview of recent developments and published literature in membrane technology, focusing on special characteristics of the membranes and membrane-based processes that are now used for the production and purification of proteins.

Prefractionation, enrichment, desalting and depleting of low volume and low abundance proteins and peptides using the MF10

The success of proteomics relies heavily in the ability to characterize very diverse species of proteins. This diversity stems from a proteins physicochemical properties, its copy number and abundance and its association with other proteins. Prefractionation and simplification of biological samples prior to downstream MS analysis is showing some virtue in obtaining greater depth of protein analysis. The MicroFlow MF10 is a prefractionation device for low volume, low abundance complex samples that can also enrich for very specific species of proteins based on charge and/or size either in native or denaturing format. It has also been used to desalt and deplete samples of contaminating ions or proteins. Although this instrument is only in its infancy in terms of exploring its capabilities, the technology has been used successfully for the fractionation of plasma proteins Wasinger(1), Omenn GS(2), as well as purification of human growth hormone Catzel D(3) antibodies Cheung(4) and IgY Gee(5) and other complex samples.

Hematologic and biochemical effects of the Gradiflow in an ex vivo ovine model

The Gradiflow (Life Therapeutics, Frenchs Forest, Australia) system is a novel electrophoretic technique that uses the dual characteristics of size and charge to separate target macromolecules from complex biological solutions. The system has the potential to selectively remove a range of moieties from blood and plasma in an in vivo system such as hemodialysis or, alternatively, in an in vitro setting such as a blood bank. In this study, the safety of a scaled down Gradiflow prototype device with a membrane surface area of 16 cm2 was investigated using an ex vivo ovine model. Physiologic, hematologic, and biochemical parameters were assessed in 12 sheep: 6 animals treated using the Gradiflow and 6 controls. The effects of the Gradiflow procedure on both whole blood and plasma were analyzed. The Gradiflow procedure was well tolerated, and the application of an electrical potential or exposure to the Gradiflow membrane did not cause any significant changes in the parameters measured. Hemoglobin levels remained stable in all groups during the 4-hour experiment. An early neutropenia was observed in all groups, although this appeared to be more pronounced with exposure to a plasma filter; the presence of the Gradiflow component had no separate influence. One sheep in the plasma group experienced septic shock, caused by Staphylococcus contamination of the separation membrane. Overall, the results indicate that there were no gross physiologic, hematologic, or biochemical adverse reactions to the ex vivo Gradiflow procedure.

TSE clearance during plasma products separation process by Gradiflow™

BACKGROUND AND OBJECTIVES

Recent experimental evidence from rodent models suggests a potential risk for transmissible spongiform encephalopathy (TSE) transmission by blood. The emergence of a new variant Creutzfeldt-Jakob disease (vCJD) has raised increased concerns about the safety of blood components and plasma products derived from vCJD-infected donors. Recent risk-minimisation strategies have included a ban on the use of UK-sourced plasma for the preparation of licensed blood products and leukodepletion of blood donations for fear of possible transmission of the human TSE via blood or blood components. The aim of this study was to investigate the capability and efficacy of a preparative electrophoresis system (Gradiflow) in the removal of TSE contaminants during the separation of plasma products.

MATERIALS AND METHODS

Using hamster adapted scrapie 263 K as a model for TSE agent, albumin and IgG separation from human plasma by Gradiflow were performed separately by spiking a 263 K scrapie microsomal fraction to the feed material at each process step. Samples from pre- and post-Gradiflow separation process were titrated to the end-point for the detection of the disease-associated, proteinase K resistant form of the pathogenic prion protein (PrP(Sc)) by Western blot.

RESULTS

Under all conditions tested, a greater than 3 log(10) reduction was achieved with no PrP(Sc) detected in any of the pooled products for either of the IgG or albumin separations. These data show that Gradiflow processing has clear advantages for concurrent purification of plasma products and in-process TSE removal.

CONCLUSIONS

Our findings suggest that Gradiflow process is a viable alternative to remove causative TSE agents during plasma products separation, potentially eliminating the risk of TSE agents transmission.

Blood protein purification and simultaneous removal of nonenveloped viruses using tangential-flow preparative electrophoresis

Gradiflow is new technology allowing purification of important blood proteins from viral contaminated plasma. Protein purification is based on unique scalable tangential-flow preparative electrophoresis, and is distinct from current technology because protein purification and virus removal are performed in the same step. This one-step removal and purification exploits both the size and charge of target proteins. The medically important blood proteins, immunoglobulin G (IgG) and alpha-1-antitrypsin, were chosen to demonstrate the ability of this process to purify proteins from contaminated plasma. Clearance factors achieved by infectivity assays and polymerase chain reaction (PCR) that meet regulatory requirements demonstrated removal of canine parvovirus (CPV). CPV is a model virus for pathogenic nonenveloped viruses, including parvovirus B19, not adequately removed or inactivated by most processes currently in practice. The recovery of proteins from plasma with high purity, recovery, and function, while simultaneously removing viruses, provides blood products with a level of purity compatible with clinical use more quickly and cheaply than available techniques.

Protein Transfer through Polyacrylamide Hydrogel Membranes Polymerized in Lyotropic Phases

A way to control the average pore size in cross-linked polyacrylamide-based membranes is by altering the ratio of cross-linker to acylamide monomer. Larger pore sizes are prepared with a minimum amount of cross-linker, resulting in membranes that are mechanically weak and have short lifetimes. The aim of this study was to prepare cross-linked polyacrylamide membranes with large pore sizes and with good mechanical integrity. The methodology was to carry out the polymerization in a template, formed from the self-aggregation of surfactant. Two surfactant templates were used, and their pore size was examined with proteins of different sizes. The surfactants chosen for this study were sodium dodecyl sulfate (SDS, ionic surfactant) and TERIC BL8 (nonionic surfactant), both of which have very different aggregation properties. The data showed that at 10% and greater of TERIC BL8, a very different and open gel structure is formed, in which the pore size was significantly increased. SDS seemed to have little effect on the pore size. The data suggests that the gel structures for both surfactants up to 4% (w/v) are similar and micellular, because SDS is known to favor a micelle structure. Above 4% (w/v), TERIC BL8 then goes through a change in its lyotropic phase, thus, producing membranes of a large pore size. In conclusion, the pore size and gel structure of polyacrylamide hydrogel membranes can be significantly increased using TERIC BL8 (nonionic) surfactant. This allows large-pore-size membranes with a high cross-link density and consequently high mechanical strength to be prepared for the separation of large biomolecules.

A Proteome Strategy for Fractionating Proteins and Peptides Using Continuous Free-Flow Electrophoresis Coupled Off-Line to Reversed-Phase High-Performance Liquid Chromatography

Extensive prefractionation is now considered to be a necessary prerequisite for the comprehensive analysis of complex proteomes where the dynamic range of protein abundances can vary from approximately 10(6) for cells to approximately 10(10) for tissues such as blood. Here, we describe a high-resolution 2D protein separation system that uses a continuous free-flow electrophoresis (FFE) device to fractionate complex protein mixtures by solution-phase isoelectric focusing (IEF) into 96 well-defined pools, each separated by approximately 0.02-0.10 pH unit depending on the gradient created, followed by rapid (approximately 6 min per analysis) reversed-phase high-performance liquid chromatography (RP-HPLC) of each FFE pool. Fractionated proteins are readily visualized in a virtual 2D format using software that plots protein loci, pI in the first dimension and relative hydrophobicity (i.e., RP-HPLC retention time) in the second dimension. By coupling a diode-array detector in line with a multiwavelength fluorescence detector, separated proteins can be monitored in the RP-HPLC eluent by both UV absorbance and intrinsic fluorescence simultaneously from a single experiment. Triplicate analyses of standard proteins using a pH 3-10 gradient conducted over a 3-day period revealed a high system reproducibility with a SD of 0.57 (0.05 pH unit) within the FFE pools and 0.003 (0.18 s) for protein retention times in the second-dimension RP-HPLC step. In addition, we demonstrate that the FFE-IEF/RP-HPLC separation strategy can also be applied to complex mixtures of low molecular weight compounds such as peptides. With the facile ability to measure the pH of the isoelectric focused pools, peptide pI values can be estimated and used to qualify peptide identifications made using either MS/MS sequencing approaches or pI discriminated peptide mass fingerprinting. The calculated peak capacity of this 2D liquid-based FFE-IEF/RP-HPLC system is 6720.

Purification of Fab fragments from a monoclonal antibody papain digest by Gradiflow electrophoresis

Fab fragments isolated from papain digests of monoclonal antibodies have a wide variety of uses in analytical and in both in vivo and in vitro diagnostic applications. A novel, non-affinity method which uses the Gradiflow to purify Fab fragments from the papain digest of a mouse IgG1 anti-c-myc monoclonal antibody is described. The Gradiflow is a preparative electrophoresis instrument that uses polyacrylamide membranes of known pore size to separate proteins in solution in their native state under mild pH conditions by charge or size. The Fab and Fc fragments from the papain digestion were characterized using isoelectric focusing (IEF) and non-reducing SDS-PAGE in conjunction with IEF and Western blot. There were three Fab isoforms with p [Formula: see text] between pH 6.5 and 7.4 while the Fc had a range of isoforms between 6.1 and 6.3. Both Fab and Fc fragments had similar [Formula: see text] of 50kDa. A charge-based purification strategy was developed to obtain a high purity Fab preparation after 10min, confirmed by Western blot and chemiluminescence analyses. A small quantity of residual undigested IgG1 remained and was removed using a size-based separation. The efficiency of the separation despite the narrow pH range between Fab and Fc suggests that this technique may be an alternative to protein A or G affinity separation of Fc and Fab monoclonal antibody fragments from papain digests of monoclonal antibodies.

The purification of IgY from chicken egg yolk by preparative electrophoresis

Chicken IgY has been purified from egg yolk by preparative electrophoresis on the Gradiflow, a system which has been employed for the purification of a wide range of proteins with high recovery and biological activity. Protein purification on the Gradiflow utilises electrophoresis with selected combinations of porous membranes and buffers. The purification of IgY was achieved by initial PEG lipid precipitation, then a single step Gradiflow run by a strategy based on the relatively high pI range of IgY compared to other egg yolk proteins. The IgY yields obtained from the delipidised supernatant are consistently greater than 80% by immunoassay. The purity of the IgY fraction compared favourably with IgY prepared using three commercial products.

Bioinformatics: how it is being used to identify bacterial vaccine candidates

Genomic sequencing has provided a tremendous amount of information that can be useful in vaccine target identification. The sheer volume of information available necessitates the use of new research disciplines and techniques. Using bioinformatics, researchers sift through available data to identify appropriate candidates for biological analysis. This review provides an overview of available bioinformatic techniques for vaccine candidate identification and a few examples of how these techniques are being applied to specific bacterial pathogens.

Electrophoretic protein transport in gold nanotube membranes

Gold nanotube membranes are ideal model systems for exploring how pore size affects the rate and selectivity of protein transport in synthetic membranes. This is because these membranes have cylindrical, monodisperse pores (the nanotubes) with diameters that can be varied at will from tens of nanometers down to less than 1 nm. We report here on the effects of nanotube inside diameter, solution pH, and applied transmembrane potential on the rate and selectivity of protein transport in PEG-thiol-treated gold nanotube membranes. The transport properties of four proteins of differing sizes and pI values--lysozyme, bovine serum albumin, carbonic anhydrase, and bovine hemoglobulin--were investigated. In general, membranes containing larger diameter nanotubes showed higher fluxes and lower selectivities than membranes with smaller diameter nanotubes. Transmembrane electrophoresis can be used to augment the diffusive transport selectivity. For example, for proteins that are oppositely charged, a combination of a large transmembrane potential and a large nanotube diameter can be used to optimize both selectivity and flux. In addition to transmembrane potential and nanotube diameter, solution pH value plays an important role in determining the transport selectivity. This is because pH determines the net charge on the protein molecule and this, in turn, determines the importance of the electrophoretic transport term.

Design of a new, twelve-channel electrophoretic apparatus based on the Gradiflow technology

The Gradiflow technology, originally designed to carry out binary, size-based and charge sign-based electrophoretic protein separations, has been extended to simultaneously obtain multiple protein fractions from a single electrophoretic separation. The separation unit of the new apparatus houses the anode and cathode compartments and up to twelve shallow separation compartments through which the background electrolyte solution that contains the separated protein fractions is recirculated. The separation compartments are formed from grids as thin as 1.2 mm and polyacrylamide membranes as thin as 0.15 mm, all with corresponding multiple inlet and outlet ports. The average pore size of the polyacrylamide membranes can be varied to permit passage of proteins in the 5000-800 000 molecular mass range. The electric field, orthogonal to the flow paths of the recirculated background electrolyte, selectively moves the sample components across the polyacrylamide separation membranes. Selective protein transport can be achieved by exploiting differences in either the relative size of the proteins or the charge sign of the proteins. The advantages of the new apparatus stem from the synergistic combination of the short electrophoretic transfer distances, high electric field strength, large effective surface areas of the separation membranes, and the great flexibility with which apparati containing one to twelve separation compartments can be created.

Preparative-scale isoelectric trapping enantiomer separations

The new Gradiflow BF200 IET unit, developed for isoelectric trapping protein separations has been modified and used to carry out preparative-scale enantiomer separations. Hydroxypropyl beta-cyclodextrin was used as the chiral resolving agent to induce an isoelectric point difference between the enantiomers. Three isoelectric membranes with isoelectric points below, in between and above the isoelectric points of the complexed enantiomers were used to trap the separated enantiomers in the anodic and cathodic separation compartments of the Gradiflow BF200 IET apparatus, respectively. The production rates were about 15 times higher than those previously obtained with another isoelectric trapping device and about 30% higher than those obtained in a continuous free-flow electrophoretic device operated in the isoelectric focusing mode. The remarkable separation speed observed in the modified Gradiflow BF200 IET unit is attributed to the favorable interplay of the short electrophoretic transfer distance, the high electric field strength and the large effective surface areas of the isoelectric membranes.

Preparation of monoclonal antibodies using the electrophoresis separation instrument, Gradiflow

Gradiflow, a preparative electrophoresis separation device, was utilized to develop and test generic protocols for the preparation of monoclonal antibodies (MAbs) from tissue culture supernatant and ascites fluid. The charge based protocol separated the high pI antibodies from the lower isoelectric points (pI) contaminants by either moving the antibody (ascites fluid) or contaminants (tissue culture supernatant) through a polyacrylamide separation membrane. A total of 60 separations were performed with tissue culture supernatant, and a further 30 separations with ascites fluid. The Gradiflow procedure resulted in higher yields, equivalent functionality and similar purity compared with affinity chromatography antibody preparation on protein A and G. The results suggest that the Gradiflow protocols may be an alternative method of antibody preparation for these samples.

Preparative-scale isoelectric trapping separations using a modified Gradiflow unit

The Gradiflow BF200 preparative electrophoretic unit (Gradipore), which has been developed for size-based and charge-sign-based protein separations and in which the hydraulic flow path of the recirculating sample stream in the separation cartridge is orthogonal to the electric field, has been modified to carry out binary protein separations using the principles of isoelectric trapping. The disposable separation cartridge contained three isoelectric membranes which, along with the cartridge holder, formed the anode and cathode compartments and the anodic and cathodic separation compartments. The utility of the modified instrument was demonstrated by effecting a binary separation of chicken egg white across an isoelectric point 5.5 isoelectric membrane. The desalting and subsequent binary separation steps proved to be remarkably rapid, due to the favorable combination of short electrophoretic path, high electric field strength and large effective isoelectric membrane surface area.

Purification of human immunoglobulin G: a new approach to plasma fractionation

BACKGROUND AND OBJECTIVES

Currently, plasma fractionation involves multiple processing steps using established methods such as ethanol precipitation and column chromatography. The known limitations associated with conventional purification techniques, combined with strict regulations on safety and high demand for particular plasma proteins, have resulted in a shortage of plasma-derived therapeutics such as intravenous immunoglobulin G (IgG).

MATERIALS AND METHODS

In this study, IgG was purified from human plasma using Gradiflow technology, an electrophoresis-based separation technology.

RESULTS

IgG was isolated from plasma to high purity, with 94 +/- 5% recovery in a short processing time.

CONCLUSIONS

The technology has been shown to be linearly scalable and has the capacity to contribute to increased production of important plasma fraction therapeutics.

Purification of the basic protein avidin using Gradiflow technology

The Gradiflow, a preparative electrophoresis instrument, which separates proteins on the basis of charge or size, was used to purify the basic protein avidin, pI 10, from chicken egg white. Using a charge based separation at pH 9.0, the high pI of avidin and lysozyme (pI 10.7) allows them to be easily separated from remaining egg white proteins, as these are the only positively charged proteins. In a second step at pH 10.2, the negatively charged avidin is separated from the positively charged lysozyme. This sequential two-step protocol was complete within 4.5h. Enzyme immunoassay of avidin fractions obtained indicated recoveries of 60-65% from one egg white with minimal lysozyme activity detected.

Preparative electrophoresis: a general method for the purification of polyclonal antibodies

Antibodies were purified from normal rabbit, sheep, goat, rat, human and bovine serum using preparative electrophoresis on a Gradiflow in a single-step process using an asymmetrical cartridge with three different pore size polyacrylamide membranes. Recoveries in each case were over 80% and were higher than those obtained using affinity chromatography on protein A, protein G or protein L. Degree of purity was at least comparable with these methods. These results suggest that preparative electrophoresis can be considered a general method for the purification of research quantities of antibodies from multiple serum sources and may be particularly useful where the reactivity with protein A, G or L is unknown.

Characterization of the pore structure of aqueous three-dimensional polyacrylamide gels with a novel cross-linker

The properties of polyacrylamide hydrogels synthesized with a novel hexafunctional (three double bonds) cross-linker, hexahydro-1,3,5-triacryloyl-s-triazine (1a), was evaluated and compared to the currently used tetrafunctional (two double bonds) cross-linker N,N-methylenebisacrylamide (Bis). A variety of characterization techniques that require very little sample preparation and data handling were chosen and include polymerization temperature profiles and conversions, water swelling, differential scanning calorimetry (DSC), polyacrylamide gel electrophoresis (PAGE), Gradiflow electrophoretic separation process and scanning electron microscopy (SEM). The alternative use of 1a compared to Bis results in polyacrylamide gels with larger pore sizes and a broad pore size distribution.