Michel Faupel

Preparative protein purification in a multi-compartment electrolyser with immobiline membranes

Abstract Preparative electrophoresis in gel phases, including isoelectric focusing, is characterized by low load limits (only a few milligrams of protein per millilitre of matrix), low recoveries (rarely exceeding 70%) and heavy contamination from neurotoxic gel material (unreacted monomers and ungrafted oligomers). A multi-compartment electrolyser is described based on the principle of highly buffering Immobiline membranes of well defined isoelectric points (pI). Each chamber is delimited by isoelectric membranes having pIs encompassing the pI value of the components of interest in the mixture to be separated. Such components are transported electrophoretically from chamber to chamber until they collect in the chamber defining their pI values. As the sample feed is kept in a number of reservoirs equal to the number of chambers in the electrolysers, at the end of the purification process each reservoir will contain, under ideal conditions, a homogeneous protein fraction. Examples of the purification of r-DNA Eglin C and of monoclonal antibodies are given.

Preparative purification of human monoclonal antibody isoforms in a multi-compartment electrolyser with immobiline membranes

The performance of a multi-compartment electrolyser with isoelectric Immobiline membranes for large-scale protein purification is evaluated. Owing to the presence of isoelectric membranes possessing a high buffering capacity and ionic strength, isoelectric protein precipitation inside the membranes, one of the major drawbacks of present membrane uses, is fully avoided. In addition, owing to this novel membrane technology, pH gradient decay, typical of isoelectric focusing in carrier ampholytes, is fully eliminated and pH and conductivity constancy is guaranteed in all flow chambers for running periods of more than 11 days (160,000 V h). The membranes described possess a unique selectivity, in that they act by modulating the surface charge (i.e., the mobility) of macroions crossing or tangential to them. The concept of isoelectric Immobiline membranes acting like a pH-stat unit is introduced. Protein homogeneity in each chamber of the electrolyser can be achieved even when purifying human monoclonal antibodies against HIV-1, which possess high pI values (9.0-9.6), are large molecules (Mr 150,000) and are fractionated in the presence of large micelles of neutral detergents.

Protein purification by Off-Gel electrophoresis

A novel free‐flow protein purification technique based on isoelectric electrophoresis is presented, where the proteins are purified in solution without the need of carrier ampholytes. The gist of the method is to flow protein solutions under an immobilised pH gradient gel (IPG) through which an electric field is applied perpendicular to the direction of the flow. Due to the buffering capacity of the IPG gel, proteins with an isoelectric point (pI) close to pH of the gel in contact with the flow chamber stay in solution because they are neutral and therefore not extracted by the electric field. Other proteins will be charged when approaching the IPG gel and are extracted into the gel by the electric field. Both a demonstration experiment with pI markers and a simulation of the electric field distribution are presented to highlight the principle of the system. In addition, an isoelectric fractionation of an Escherichia coli extract is shown to illustrate the possible applications.

Isoelectric protein purification by orthogonally coupled hydraulic and electric transports in a segmented immobilized pH gradient

A new method is described for preparative protein purification, based on isoelectric focusing on immobilized pH gradients. The principle is entirely new, as it is based on keeping the protein of interest isoelectric, in a flow-chamber, and focusing the impurities in the Immobiline gel. For this, a hydraulic flow is coupled orthogonally to an electric flow, sweeping away the non-isoelectric impurities from the recycling chamber. The sample flow-chamber is built in the centre of the apparatus, and is coupled to an upper and lower segment of an immobilized pH gradient. The protein to be purified is kept isoelectric in the flow-chamber and prevented from leaving it by arranging for the extremities of the immobilized pH gradient, forming the ceiling and the floor of this chamber, to have isoelectric points just higher (e.g. +0.05 pH units, on the cathodic side) and just lower (e.g. -0.05 pH units, on the anodic side) than the known pI of the species of interest. Macromolecules and small ions leave the flow chamber at a rate corresponding to a first order reaction kinetics (the plot of log C vs. time being linear). In general, for macromolecules, 12 h of recycling under current allow removal of 95% impurities. After 24 h of recycling, the protein of interest is more than 99.5% pure. The recoveries are very high (approaching 100%) as the sample under purification never enters the Immobiline gel and thus does not have to be extracted from a hydrophilic matrix, as typical of preparative gel electrophoresis.

A horizontal apparatus for isoelectric protein purification in a segmented immobilized pH gradient

A modification of the previously described apparatus (Faupel et al. (1987) J. Biochem. Biophys. Methods 15, 147-162), for recycling isoelectric focusing in a segmented immobilized pH gradient, is here reported. The most important improvements are: (1) a horizontal, vs. the previously vertical assembly; (2) a reduction of the thickness of the central flow chamber to 6 mm, vs. the previous 3 cm length and (3) the introduction, at both gel extremities of each Immobiline segment, of polypropylene filters, thus efficiently blocking the gel in situ. The advantages are: (i) the spontaneous removal of air bubbles, which in the vertical apparatus tend to accumulate in the ceiling of the flow chamber and to obstruct the flow of electric current; (ii) a more efficient hydraulic flow with a reduced chance of heating the liquid stream in the flow chamber, due to its reduced length along the separation path and (iii) a reduced risk of gel detachment from the tube walls, due to osmotic swelling caused by focused protein zones in the gel phase and by the fixed Immobiline charges in the polyacrylamide matrix.

Protein desalting by isoelectric focusing in a segmented immobilized pH gradient

We have recently described an apparatus for protein purification based on a segmented Immobiline gel, having one or more liquid interlayers in between. The principle is entirely new, as it is based on keeping the protein of interest isoelectric, in a flow chamber, and focusing the impurities in an Immobiline gel. For this, a hydraulic flow is coupled orthogonally to an electric flow, sweeping away the non-isoelectric impurities from the recycling chamber. We now demonstrate that the present apparatus can be efficiently used for protein desalting. Hemoglobin A samples, containing 50 mM NaCl or 50 mM ammonium acetate, could be efficiently desalted in 2 h of recycling, after which the total salt content had decreased to less than 0.005 mM (a salt decrement of more than 10,000 fold the initial input). However, with polyprotic buffers (sulphate, citrate, phosphate, oligoamines) the desalting process was much slower, typically of the order of 20 h, possibly due to interaction of these species with the surrounding Immobiline matrix. In this last case, outside pH control (e.g. with a pH-stat) is necessary during protein purification, as, due to the faster removal of the monovalent counterion, the solution in the recycling chamber can become rather acidic or alkaline. It is demonstrated that the 2 extremities of the Immobiline segments facing the sample recycling chamber act indeed as isoelectric membranes, having a good buffering capacity, preventing the protein macroion from leaving the chamber by continuously titrating it to its isoelectric point.

Capillary zone electrophoresis for monitoring r-DNA protein purification in multi-compartment electrolysers with immobiline membranes

Isoforms of human monoclonal antibodies against the gp-41 of AIDS virus and of human recombinant superoxide dismutase have been purified to homogeneity by isoelectric focusing (IEF) in a multi-compartment electrolyser with isoelectric, immobiline membranes. This system allows the processing of large sample volumes and gram-scale protein loads and can resolve isoforms as close as 0.001 in pI difference. The purification progress was usually monitored by analytical IEF in immobilized pH gradients (IPG). Capillary zone electrophoresis (CZE) was applied to the monitoring of the content of each chamber of the electrolyser. CZE was found to be superior in terms of speed of analysis and quantification (but only by UV reading at 200-210 nm, i.e., in the region of the peptide bond) but, notwithstanding the millions of theoretical plates reported, was no match for the resolving power of IPGs, at least for protein analysis. When compared also with chromatofocusing, the resolving power decreases in the order IPG greater than CZE much greater than chromatofocusing.

Large-scale electrophoresis for protein purification: exploiting isoelectricity

Abstract Preparative electrophoresis methods (including isoelectric focusing in immobilized pH gradients) in gel phases are characterized by low loadings barely a few mg protein per ml matrix), low recoveries (rarely exceeding 70%), and heavy contamination from neurotoxic gel materials (the unreacted gel monomers and ungrafted oligomers). These drawbacks can be minimized by a version of isoelectric focusing in which the need for protein of interest to pass the gel is eliminated: only the contaminants traverse the gel. This is achieved by circulating a liquid sample between two gels held at controlled pHs. The method can provide: (1) high rate of sample processing (up to 1 g h −1 ); (2) high purification (in general to charge homogeneity); and (3) high recoveries (>95%). A large-scale membrane apparatus has been built, with a cross- sectional diameter of 9 cm. Large Pt electrode disks provide even current flow. In this electrolyser, 10 g of Eglin C (produced by recombinant DNA technology) have been purified to homogeneity in around 10 h from 1 l of a partially enriched preparation.

Useful modification of Pauly's reagent : Detection of low-molecular-weight histidine-containing peptides by isoelectric focusing

Abstract An improved method for the detection of low-molecular-weight ( The major advantage of the method is that the staining mixture (a modification of Paulys raegent) does not react with ampholytes of similar size and pI, permitting accurate determination of the isoelectric points of these peptides.

Separation of formoterol enantiomers and detection of zeptomolar amounts by capillary electrophoresis using laser-induced fluorescence

Abstract A sensitive and rapid high-performance capillary electrophoresis (HPCE) method combined with laser-induced fluorescence (LIF) detection is described, which is suitable for the analysis of racemic formoterol and formoterol enantiomers after derivatization with fluorescein isothiocyanate (FITC). The limit of detection is 1 pg/ml in the case of FITC-derivatized racemic formoterol in the absence of chiral selector. Upon injection of 5 nl, it corresponds to an amount of not more than 120 molecules. The chiral recognition occurs in the presence of heptakis(2,3,6-tri-O-methyl-β-cyclodextrin) as a chiral selector in the buffer electrolyte and yields a detection limit of 10·10 −12 g/ml for each enantiomer.