New solution IEF device for micropreparative separation of peptides and proteins: General

Recent advances in isoelectric focusing of proteins and peptides

This review article describes the significant recent advances in Isoelectric Focusing from the period 2015-2020. The review highlights the principles and common challenges faced in Isoelectric Focusing as well as its applications. This review also details the recent advances in various modes of Isoelectric Focusing in various platforms and future directions for the technique.

DNA purification and concentration by isotachophoresis in nonwoven fabric strip

We present a novel method for concentration and purification of DNA from biological samples. The method is based on isotachophoretic separation of DNA strands in a separation bed made of a disposable nonwoven fabric strip. Application of oxalate as the leading ion prevented corrosion of the carbon anode and also the leading ion was continually removed from the system due to its decomposition into CO₂ at the anode. The fractions were marked by three colored markers of electrophoretic mobility closely surrounding the mobility of DNA. The fraction collection was realized by a centrifugal drain of cut out strip segments. The method was evaluated using two purified salmon sperm DNA fragments of lengths 200 bp and 2000 bp. The results confirmed the high DNA concentrating effect of the method (34-fold increase of the original DNA concentration). The composition of running solutions and voltage program were optimized in order to finish the analysis within 30 min. The optimized method was used to extract, concentrate and purify DNA from a crude yeast cell lysate. The maximum DNA enrichment factor decreased to 12 due to the stretching of DNA zones caused by low-molecular contaminants present in the original lysate. The average recovery determined for yeast DNA was 71 ± 11% (n = 3). The connected elimination of the proteins from DNA zones resulted in the purification factor value of 582 for DNA vs proteins. This demonstrates that the presented method is capable to concentrate DNA from the bulk volume and to further purify it from crude cell lysates using a simple instrumentation and low-cost disposable separation bed.

Utilization of Red Nonionogenic Tenside Labeling, Isoelectric Focusing, and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry in the Identification of Uropathogens in the Presence of a High Level of Albumin

Cellulose-based preparative isoelectric focusing was used for preseparation and concentration of uropathogens Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, Staphylococcus epidermidis, Candida albicans, and Candida parapsilosis in a urine sample containing a high concentration of human serum albumin. For the visibility of the colorless microbial zones in the separation medium, the microbial cells were labeled with red nonionogenic tenside (1-[[4-(phenylazo)phenyl]azo]-2-hydroxy-3-naphthoic acid polyethylene glycol ester, PAPAN). A very short incubation time, about 2 min, was sufficient for the adsorption of 0.001% (w/v) PAPAN onto the cell surface at the optimized conditions. As low as 10³ cells of E. coli (pI 4.6) resuspended in 100 μL of urine sample and spiked with 0.1 mg mL^-1 of human serum albumin (pI 4.8) were successfully preseparated and concentrated using this method. Because the pI values of the labeled microorganisms remained unchanged, the focused red zones of microbial cells were collected from the separation media and further analyzed by either capillary isoelectric focusing or matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The viability of the cells extracted from the collected zones was also confirmed. The proposed method provides reliable, relatively fast, and cost-effective identification of uropathogens in urine specimens with a high level of albumin.

Preparative and capillary isoelectric focusing for detection and identification of Aspergillus conidia in complex sample matrices

This study describes a new method for fast identification of highly hydrophobic conidia of Aspergillus species from both simple and complex matrices. The method is based on recently developed preparative isoelectric focusing in a cellulose-based separation medium which had to be modified with respect to the highly hydrophobic surface of the conidia. Although Aspergillus conidia are colored, their zones in the cellulose bed were indicated by colored isoelectric point markers. The isoelectric point values of Aspergillus conidia were determined by capillary isoelectric focusing. Preparative isoelectric focusing was successfully used for preconcentration of individual conidia of cultivated strains of Aspergillus niger, Aspergillus fumigatus, Aspergillus flavus, and Aspergillus parasiticus, and also for separation of the conidia in a mixture. Subsequently, red pepper powder and peanuts spiked with Aspergillus niger and Aspergillus flavus conidia, respectively, were used as complex matrices. The detection limit for identification of the conidia in these complex matrices is 10⁴ conidia mL^-1 . The presence of conidia in the focused zones was confirmed by their subsequent analysis by capillary isoelectric focusing. Their viability was confirmed by a cultivation of the conidia extracted from the collected fractions after preparative isoelectric focusing.

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.

Preparative isoelectric focusing in a cellulose-based separation medium

An improved preparative method based on isoelectric focusing of analytes in a cellulose-based separation medium is described in this study. Cellulose is suspended in an aqueous solution of simple buffers, ethylene glycol, glycerol, nonionic surfactant, and colored pI markers. Water partially evaporates during focusing run and the separation takes place in an in situ generated layer of cellulose, which has a gel-like appearance at the end of analysis. Final positions of analytes are indicated by the positions of zones of focused pI markers. Fractions, segments of the separation medium with analytes, can be simply collected by spatula and analyzed by downstream analytical methods. Good focusing ability of the new method and almost quantitative recovery of model proteins, cytochrome c and bovine serum albumin, was verified by gel electrophoresis and capillary isoelectric focusing of the collected fractions.

An innovative ring-shaped electroeluter for high concentration preparative isolation of protein from polyacrylamide gel

A ring-shaped electroeluter (RSE) was designed for protein recovery from polyacrylamide gel matrix. The RSE was designed in such a way that a ring-shaped well was used to place gel slices and an enrichment well was used to collect eluted protein samples. With HSA as model protein, the electroelution time was less than 30 min with 80% recovery rate, and the concentration of recovered protein was 50 times higher than that of conventional method. The RSE could be reused at least ten times. The developed device makes great advance towards economic electroelution of biomolecules (such as proteins) from gel matrix.

A novel microscale preparative gel electrophoresis system

A novel microscale preparative gel electrophoresis system is designed and manufactured for protein separation and preparation.