INTERVAL CARRIER FREE ELECTROPHORESIS FOR HIGH RESOLUTION PROTEIN PURIFICATION

Partial Purification of a Megadalton DNA Replication Complex by Free Flow Electrophoresis

We describe a gentle and rapid method to purify the intact multiprotein DNA replication complex using free flow electrophoresis (FFE). In particular, we applied FFE to purify the human cell DNA synthesome, which is a multiprotein complex that is fully competent to carry-out all phases of the DNA replication process in vitro using a plasmid containing the simian virus 40 (SV40) origin of DNA replication and the viral large tumor antigen (T-antigen) protein. The isolated native DNA synthesome can be of use in studying the mechanism by which mammalian DNA replication is carried-out and how anti-cancer drugs disrupt the DNA replication or repair process. Partially purified extracts from HeLa cells were fractionated in a native, liquid based separation by FFE. Dot blot analysis showed co-elution of many proteins identified as part of the DNA synthesome, including proliferating cell nuclear antigen (PCNA), DNA topoisomerase I (topo I), DNA polymerase δ (Pol δ), DNA polymerase ɛ (Pol ɛ), replication protein A (RPA) and replication factor C (RFC). Previously identified DNA synthesome proteins co-eluted with T-antigen dependent and SV40 origin-specific DNA polymerase activity at the same FFE fractions. Native gels show a multiprotein PCNA containing complex migrating with an apparent relative mobility in the megadalton range. When PCNA containing bands were excised from the native gel, mass spectrometric sequencing analysis identified 23 known DNA synthesome associated proteins or protein subunits.

Free-flow electrophoresis in proteome sample preparation

An aim of proteome research is to identify the entire complement of proteins expressed in defined cell types of humans, animals, plants, and microorganisms. The approach requires searching for low abundant or even rarely expressed proteins in many cell types, as well as the determination of the protein expression levels in subcellular compartments and organelles. In recent years, rather powerful MS technologies have been developed. At this stage of MS device development, it is of highest interest to purify intact cell types or isolate subcellular compartments, where the proteins of interest are originating from, which determine the final composition of a peptide mixture. Free-flow electrophoresis proved to be useful to prepare meaningful peptide mixtures because of its improved capabilities in particle electrophoresis and the enhanced resolution in protein separation. Sample preparation by free-flow electrophoresis mediated particle separation was preferentially performed for purification of either organelles and their subspecies or major protein complexes. Especially, the introduction of isotachophoresis and interval zone electrophoresis improved the purity of the gained analytes of interest. In addition, free-flow IEF proved to be helpful, when proteins of low solubility, obtained, e.g. from cell membranes, were investigated.

Isolation of monodisperse nanodisc-reconstituted membrane proteins using free flow electrophoresis

Free flow electrophoresis is used for rapid and high-recovery isolation of homogeneous preparations of functionally active membrane proteins inserted into nanodiscs. The approach enables isolation of integral and membrane anchored proteins and is also applicable following introduction of, e.g., fluorescent tags. Preparative separation of membrane protein loaded nanodiscs from empty nanodiscs and protein aggregates results in monodisperse nanodisc preparations ideal for structural and functional characterization using biophysical methods.

Resolution of adiponectin oligomers in human plasma using free flow electrophoresis

Adiponectin is an important adipocytokine hormone which circulates in blood as homo-oligomers (trimer, hexamer and high molecular weight (HMW) forms) as well as a truncated form corresponding to the globular domain. Free flow electrophoresis (FFE) used in zone electrophoresis mode revealed the presence of isoforms within these oligomeric forms in plasma. HMW adiponectin oligomer showed two isoforms which carry different charge density at pH 4.7, only one of which is susceptible to dissociation by SDS. The adiponectin hexamer was shown to consist of a doublet and also shown to have at least two isoforms. A truncated form of adiponectin was identified as the main constituent of adiponectin in plasma and appeared to circulate bound to a basic protein, potentially one of the chemokines reported to bind to the globular domain. Analysis of the monomer composition of the oligomers revealed differences in monomeric isoforms used to build up the oligomers.

From micro to macro: conversion of capillary electrophoretic separations of biomolecules and bioparticles to preparative free-flow electrophoresis scale

This invited contribution in the special issue of Electrophoresis published in celebration of the 30th Anniversary of this journal reflects the impact of our milestone paper [Prusík, Z., Kasicka, V., Mudra, P., Stepánek, J., Smékal, O., Hlavácek, J., Electrophoresis 1990, 11, 932-936] in the area of conversion of microscale analytical and micropreparative CE separations of biomolecules and bioparticles into (macro)preparative free-flow electrophoresis (FFE) scale on the basis of a correlation between CE and FFE methods. In addition to the survey of advances in the relatively narrow field of CE-FFE correlation and CE-FFE conversion, a comprehensive review of the recent developments of micropreparative CE and (macro)preparative FFE techniques is also presented and applications of these techniques to micro- and (macro)preparative separations and purifications of biomolecules and bioparticles are demonstrated. The review covers the period since the year of publication of the above paper, i.e. ca. the last 20 years.

Free-flow electrophoresis in a microfabricated chamber with a micromodule fraction separator. Continuous separation of proteins

Continuous free flow electrophoresis of proteins was carried out in a microfabricated free flow electrophoresis (mFFE) module with the 30-microm thick slit of the separation. The newly developed micromodule fraction separator (MFS) was attached to the down-stream end site of the separation chamber of mFFE. By using the MFS, electrolyte solution from the separation chamber was introduced to the peristaltic pump without disturbing the electrolyte solution flow at the bottom side of the chamber. The separation of protein mixture samples was achieved by a hydroxypropylmethylcellulose pretreatment coating of the separation chamber. The pretreatment of the sample chamber effectively suppressed electroosmotic flow. All fractionated samples were collected using the MFS after continuous elecrophoresis and analyzed by reversed-phase HPLC. From the results of HPLC analyses none of the cytochrome c fractions at the other ports revealed cross talk phenomena at adjacent ports. A similar result occurred for the myoglobin. This means that these proteins were completely separated from each other by continuous mFFE, and the MFS functioned efficiently during continuous electrophoresis.

Improved preparative-scale. continuous, free-flow electrophoretic separation of the enantiomers of terbutaline utilizing equal-but-opposite enantiomer mobilities

The factors that influence yield and product purity in the continuous, preparative-scale electrophoretic separation of the enantiomers of terbutaline when using the principle of equal-but-opposite effective mobilities were studied. The sodium salt of heptakis-6-sulfato-beta-cyclodextrin was used as the resolving agent, in acidic, isopropanol-containing background electrolytes, in the continuous, free-flow, preparative electrophoretic instrument, the Octopus. By matching the linear velocity of the feed solution to that of the background electrolyte, lateral hydrodynamic dispersion was minimized resulting in a nonelectrophoresed feed band that was only three fractions (about 3 mm) wide as it exited the 0.5 m long separation channel. The multiple of residence time and applied potential was also optimized, constrained by migration of the front of heptakis-6-sulfato-beta-cyclodextrin out of the separation zone, leading to the recovery of 95% of both enantiomers in better than 99.99% purity, at a production rate of 0.1 mg/h.

Use of single-isomer, multiply charge chiral resolving agents for the continuous, preparative-scale electrophoretic separation of enantiomers based on the principle of equal-but-opposite analyte mobilities

A novel approach to continuous, preparative-scale electrophoretic enantiomer separations has been developed based on the observation that stable, equal-but-opposite effective mobilities can be created for the enantiomers of a single-charged analyte by complexing them with a single-isomer, multiply charged resolving agent, provided that the charge of the resolving agent is opposite in sign to that of the uncomplexed analyte enantiomers. When such an analyte-resolving agent system is fed into a continuous, free-flow electrophoretic apparatus, stable, steady-state operating conditions can be established which permit the continuous feeding of the racemic analyte and the collection of pure enantiomers at the opposite sides of the feed stream. This concept is demonstrated via the separation of the enantiomers of terbutaline using heptakis-6-sulfato beta-cyclodextrin as resolving agent, affording production rates as high as 2.8 mg/h in the general-purpose, continuous free-flow electrophoretic system, the Octopus.

Separation of plant membranes by electromigration techniques

The review focuses on the multiple separating regimes that offers the free flow electrophoresis technique: free flow zone electrophoresis, isoelectric focusing, isotachophoresis, free flow step electrophoresis. Also, the feasibility to apply either interval or continuous flow electrophoresis is evaluated. The free flow zone electrophoresis regime is generally selected for the separation of cells, organelles and membranes while the other regimes find their largest fields of applications in the purification of proteins and peptides. The latter regimes present the highest resolution efficiency. Therefore, a large part of this review is devoted to the applicabilities of these different regimes to the purification of organelles and membrane vesicles at the preparative scale. Recent developments, both in instrumentation and procedures, are described. The major achievements in plant membrane fractionation obtained with free flow electrophoresis are outlined. The related procedures are both analytical and preparative: they separate tonoplast and plasma membrane simultaneously from the same homogenate, they discriminate for one type of membrane vesicles of opposite orientation, and process large quantities of membrane material by reason of the continuous flow mode. Recent advances using electromigration techniques that permit confirmation of the dynamic state of membranes, characterisation of complex membrane-dependent functions and discovery of new membrane-localised activities are presented.

Interval isotachophoresis for purification and isolation of ionogenic species

A new preparative electrophoretic method in free solution is described, consisting of three consecutive steps: (i) filling the separation chamber with a suitable electrolyte system and sample in parallel streams by laminar hydrodynamic flow, (ii) applying the voltage across the chamber with isotachophoretic separation for a definite time interval operating in the direction perpendicular to that of filling, (iii) reapplying a hydrodynamic flow (without voltage) and collecting the separated species via an array of outlets. This approach completely eliminates the main drawback of the continuous flow electrophoresis (CFE), i.e., the electrohydrodynamic distortion of zones. This method utilizes the instrumentation devised for CFE and enables the isolation of large amounts of individual sample species comparable to that of CFE, with a resolution comparable to that of capillary isotachophoresis. The precise timing of the consecutive steps in the procedure as well as the stability of the operational parameters are of key importance for reproducibility. By using cationic isotachophoresis with 3 synthetic pI markers as model sample species, the reproducibility, stability and the separation power of the newly presented method are demonstrated. The sample throughput corresponds to micromoles per hour.

Recent developments in preparative free flow isoelectric focusing

Continuous flow electrophoresis (CFE) is a promising method for preparative fractionation of a variety of biological species, ranging from peptides and proteins to subcellular particles and cells. The high separation efficiency of FFE may be deteriorated by hydrodynamic distortion of zones due to the omnipresent parabolic laminar flow profile. We show in this paper that the detrimental hydrodynamic distortion of separated proteins zones can be reduced, with resultant enhancement of separation efficiency, by employing continuous isoelectric focusing in pH gradients as the actual working regime in an advanced instrumentation. Newly developed media for fast generation of narrow- or broad-range pH gradients under CFE conditions are described. The separation efficiency of these pH gradients is comparable to that of the gradients formed with the aid of synthetic carrier ampholytes. The new media are defined mixtures of nontoxic chemicals, and thus they are compatible with the requirements of human medicine. Experimental data are given showing that the new media offer fractionation of isoforms of proteins, that they offer resolution of proteins differing in isoelectric point (pI) by less than 0.05 pH units, and that these media inhibit proteins precipitation in experiments with human serum proteins.

Counterbalancing hydrodynamic sample distortion effects increases resolution of free-flow zone electrophoresis

On fractionation of highly heterogeneous protein mixtures, optimal resolution was achieved by forcing proteins to migrate through a preestablished pH gradient, until they entered a medium with a pH similar but not equal to their pIs. For this purpose, up to seven different media were pumped through the electrophoresis chamber so that they were flowing adjacently to each other, forming a pH gradient declining stepwise from the cathode to the anode. This gradient had a sufficiently strong band-focusing effect to counterbalance sample distortion effects of the flowing medium as proteins approached their isoelectric medium closer than 0.5 pH units. Continuous free-flow zone electrophoresis (FFZE) with high throughput capability was applicable if proteins did not precipitate or aggregate in these media. If components of heterogeneous protein mixtures had already started to precipitate or aggregate, in a medium with a pH exceeding their pI by more than 0.5 pH units, the application of interval modus and media forming flat pH gradients appeared advantageous.