Effect of salt concentration on separation patterns in static capillary isoelectric focusing with imaging detection

Strategies for capillary electrophoresis: Method development and validation for pharmaceutical and biological applications-Updated and completely revised edition

This review is in support of the development of selective, precise, fast, and validated capillary electrophoresis (CE) methods. It follows up a similar article from 1998, Wätzig H, Degenhardt M, Kunkel A. "Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications," pointing out which fundamentals are still valid and at the same time showing the enormous achievements in the last 25 years. The structures of both reviews are widely similar, in order to facilitate their simultaneous use. Focusing on pharmaceutical and biological applications, the successful use of CE is now demonstrated by more than 600 carefully selected references. Many of those are recent reviews; therefore, a significant overview about the field is provided. There are extra sections about sample pretreatment related to CE and microchip CE, and a completely revised section about method development for protein analytes and biomolecules in general. The general strategies for method development are summed up with regard to selectivity, efficiency, precision, analysis time, limit of detection, sample pretreatment requirements, and validation.

Surface isoelectric focusing (sIEF) with carrier ampholyte pH gradient

Isoelectric focusing (IEF) is a powerful tool for amphoteric protein separations because of high sensitivity, bio-compatibility, and reduced complexity compared to chromatography or mechanical separation techniques. IEF miniaturization is attractive because it enables rapid analysis, easier adaptation to point of care applications, and smaller sample demands. However, existing small-scale IEF tools have not yet been able to analyze single protein spots from array libraries, which are ubiquitous in many pharmaceutical discovery and screening protocols. Thus, we introduce an in situ, novel, miniaturized protein analysis approach that we have termed surface isoelectric focusing (sIEF). Low volume printed sIEF gels can be run at length scales of ∼300 μm, utilize ∼0.9 ng of protein with voltages below 10 V. Further, the sIEF device platform is so simple that it can be integrated with protein library arrays to reduce cost; devices demonstrate reusability above 50 uses. An acrylamide monomer solution containing broad-range carrier ampholytes was microprinted with a Nano eNabler^TM between micropatterned gold electrodes spaced 300 μm apart on a glass slide. The acrylamide gel was polymerized in situ followed by protein loading via printed diffusional exchange. A pH gradient formed via carrier ampholyte stacking when electrodes were energized; the gradient was verified using ratiometric pH-sensitive FITC/TRITC dyes. Green fluorescent protein (GFP) and R-phycoerythrin (R-PE) were utilized both as pI markers and to test sIEF performance as a function of electric field strength and ampholyte concentration. Factors hampering sIEF included cathodic drift and pH gradient compression, but were reduced by co-printing non-ionic Synperonic® F-108 surfactant to reduce protein-gel interactions. sIEF gels achieved protein separations in <10 min yielding bands < 50 μm wide with peak capacities of ∼8 and minimum pI differences from 0.12 to 0.14. This new sIEF technique demonstrated comparable focusing at ∼100 times smaller dimensions than any previous IEF. Further, sample volumes required were reduced four orders of magnitude from 20 μL for slab gel IEF to 0.002 μL for sIEF. In summary, sIEF advantages include smaller volumes, reduced power consumption, and microchip surface accessibility to focused bands along with equivalent separation resolutions to prior IEF tools. These attributes position this new technology for rapid, in situ protein library analysis in clinical and pharmaceutical settings.

Rapid quantitative analysis of monoclonal antibody heavy and light chain charge heterogeneity

An alternative method to traditional 2-dimensional gel electrophoresis (2D-PAGE) and its application in characterizing the inherent charge heterogeneity of chromatographically isolated monoclonal antibody heavy and light chains is described. This method, referred to as ChromiCE, utilizes analytical size-exclusion chromatography (SEC), performed under reducing and denaturing conditions, followed by imaged capillary isoelectric focusing (icIEF) of the chromatographically separated heavy and light chains. Under conditions suitable for the subsequent icIEF analysis, the absolute and relative SEC elution volumes of the heavy and light chains were found to be highly pH dependent, a phenomenon that can be exploited in optimizing chromatographic separation. Compared to 2D-PAGE, the ChromiCE method substantially decreases the time and labor needed to complete the analysis, improves reproducibility, and provides fully quantitative assessment of charge heterogeneity. The ChromiCE methodology was applied to a set of diverse monoclonal antibodies to demonstrate suitability for quantitative charge variant analysis of heavy and light chains. A typical application of ChromiCE in extended characterization and stability studies of a purified antibody is shown.

Electrical conductivity as a tool to detect salt in clinical proteomics samples

Clinical proteomics encompasses the study of the proteins in the human body at different settings to understand the various physiological and pathological pathways. The processing of the samples for electrophoresis based proteomics is a challenge to any researcher. Salt in particular can have an array of effects during the electrophoretic separation of proteins. There is a definite need to determine the concentration of salts in the samples and the effectiveness of salt removing protocols on small volume samples. A simple-cost effective technique to know the salt concentration in the clinical proteomics samples has been highlighted in the report. The application will be of value in a developing country such as India.

Characterization of plant growth-promoting rhizobacteria using capillary isoelectric focusing with whole column imaging detection

Capillary isoelectric focusing (cIEF) can be a useful tool for the characterization and identification of microbes. Based on the whole column imaging detection (WCID) technique and using plant growth-promoting rhizobacteria (PGPR) as test microbes, we present a two-level cIEF characterization method for the characterization and identification of bacteria. Intact bacteria were first characterized according to their apparent isoelectric points measured by cIEF-WCID and then lysed bacteria were further characterized by cIEF profiling of the intracellular proteins. Cellular clustering was found to be the main experimental barrier for the characterization of intact bacteria. The addition of sodium chloride (100mM) to the sample mixture was found to be an effective way to reduce clustering. Due to the high efficiency and high resolution of cIEF-WCID, characterization of bacteria according to their intracellular proteins can be implemented simply and quickly without optimization of the experimental conditions. To improve the detection sensitivity with laser induced fluorescence (LIF)-WCID, the possibility to label bacteria with a non-covalent fluorescent dye, NanoOrange, was explored.

Peak identification in capillary isoelectric focusing using the concept of relative peak position as determined by two isoelectric point markers

In CIEF analysis, sample peaks can be identified by their relative peak positions (RPP) that are determined using only two internal pI markers. The two internal pI marker peaks should bracket, as close as possible, the sample peaks. The RPP values of the sample peaks are then calculated using the pI values, peak positions of the two pI markers, and peak position of the sample. Use of this method can effectively compensate for pH gradient distortions that often occur as a result of salts. Also, as shown by the results of this paper, regardless of the linearity of the pH gradient established by the given carrier ampholytes, sample peaks can be identified within an SD of 0.1 pH unit in RPP (<2% RSD) as long as the sample is run using the same carrier ampholytes and maintaining salt concentrations in the range of 0-15 mM.

Determination of the isoelectric point of proteins by capillary isoelectric focusing

Different ways of determining isoelectric points (pI) of proteins in capillary isoelectric focusing are reviewed here. Due to the impossibility of direct pH measurements in the liquid phase, such assessments have to rely on the use of pI markers. Different types of pI markers have been described: dyes, fluorescently labelled peptides, sets of proteins of known pI values. It appears that, perhaps, the best system is a set of 16 synthetic peptides, trimers to hexamers, made to contain each a Trp residue for easy detection at 280 nm. By a careful blend of acidic (Asp, Glu), mildly basic, with pK around neutrality (His), and basic (Lys, Arg) amino acids, it is possible to obtain a series of pI markers with pI values quite evenly distributed along the pH scale, possessing good buffering capacity and conductivity around their pI values and thus focusing as sharp peaks. Another approach to pI determination is the monitoring of the current during mobilization: this allows, with the aid of known pI markers, to calibrate the system with a pI/current graph. Pitfalls and common errors in pI determinations are reviewed here and guidelines given for minimizing such errors in pI estimation.

Capillary electrophoresis of proteins 1999-2001

This review article with 223 references describes recent developments in capillary electrophoresis (CE) of proteins and covers papers published during last two years, from the previous review (V. Dolnik, Electrophoresis 1999, 20, 3106-3115) through Spring 2001. It describes the topics related to CE of proteins including modeling of the electrophoretic properties of proteins, sample pretreatment, wall coatings, improving selectivity, detection, special electrophoretic techniques, and applications.