Capillary sodium dodecyl sulfate gel electrophoresis of proteins II. On the Ferguson method in polyethylene oxide gels

A comparative study of CE-SDS, SDS-PAGE, and Simple Western: Influences of sample preparation on molecular weight determination of proteins

The development of capillary electrophoresis, especially CE-SDS devices, has led CE-SDS to become an established tool in a wide range of applications in the analysis of biopharmaceuticals and is increasingly replacing its method of origin, SDS-PAGE. The goal of this study was to evaluate the comparability of molecular weight (MW) determination especially by CE-SDS and SDS-PAGE. For ensuring comparability, model proteins that have little or no posttranslational modifications and an IgG antibody were used. Only a minor influence of sample preparation conditions, including sample buffer, temperature conditions, and different reducing agents on the MW determination were found. In contrast, the selection of the MW marker plays a decisive role in determining the accurate apparent MW of a protein. When using different MW markers, the deviation in MW determination can exceed 10%. Interestingly, CE-SDS and 10% SDS-PAGE hardly differ in their trueness of MW determination. The trueness in relation to the reference MW for each protein was calculated. Although the trueness values for the model proteins considered range between 1.00 and 1.11 using CE-SDS, they range between 0.93 and 1.03 on SDS-PAGE, depending on the experimental conditions chosen.

Size separation of proteins by capillary zone electrophoresis with cationic hitchhiking

The paper describes a method of size separation of proteins by capillary sieving electrophoresis with cationic surfactant. Proteins are separated within 12 min with repeatability of migration times better than 0.2%. Some proteins achieve the separation efficiency of 200,000 theoretical plates. The method can be used for determination of protein relative molecular masses. The accuracy of the determined relative molecular masses and the limitation of the method were investigated by the analysis of more than 60 proteins. The method also allows separation of protein oligomers. Proteins can be quantitated after the electrokinetic injection in the concentration range 0.07-0.43 g/L. The average detection limit is about 2 mg/L.

Chemical modification of proteins to improve the accuracy of their relative molecular mass determination by electrophoresis

We studied the electrophoretic behavior of basic proteins (cytochrome c and histone III) and developed a carbamylation method that normalizes their electrophoretic size separation and improves the accuracy of their relative molecular mass determined electrophoretically. In capillary zone electrophoresis with cationic hitchhiking, native cytochrome c does not sufficiently bind cationic surfactants due to electrostatic repulsion between the basic protein and cationic surfactant. Carbamylation suppresses the strong positive charge of the basic proteins and results in more accurate relative molecular masses.

Microchip Laser-Induced Fluorescence Detection of Proteins at Submicrogram per Milliliter Levels Mediated by Dynamic Labeling under Pseudonative Conditions

We have previously demonstrated on-column dynamic labeling of protein-SDS complexes on capillaries and microchips for laser-induced fluorescence (LIF) detection using both a commercially available fluor and a protein separation buffer. Upon binding to hydrophobic moieties (of the analyte or separation buffer), the fluor undergoes a conformational change allowing fluorescence detection at 590 nm following excitation with 488-nm light. Our original work showed on-chip limits of detection (LOD) comparable with those using UV detection (1 x 10(-5) M) on capillaries-falling significantly short of the detection limits expected for LIF. This was largely a function of the physicochemical characteristics of the separation buffer components, which provided significant background fluorescence. Having defined the contributing factors involved, a new separation buffer was produced which reduced the background fluorescence and, consequently, increased the available dye for binding to protein-SDS complexes, improving the sensitivity in both capillaries and microchips by at least 2 orders of magnitude. The outcome is a rapid, sensitive method for protein sizing and quantitation applicable to both capillary and microchip separations with a LOD of 500 ng/mL for bovine serum albumin. Interestingly, sensitivity on microdevices was improved by inclusion of the dye in the sample matrix, while addition of dye to samples in conventional CE resulted in a drastic reduction in sensitivity and resolution. This can be explained by the differences in the injection schemes used in the two systems. The linear range for protein quantitation covered at least 2 orders of magnitude in microchip applications. On-chip analysis of human sera allowed abnormalities, specifically the presence of elevated levels of gamma-globulins, to be determined.

Rapid determination of protein molecular weight by the Ferguson method and multiplexed capillary electrophoresis

A method based on the use of the Ferguson method and multiplexed sodium dodecyl sulfate-capillary gel electrophoresis (SDS-CGE) with UV detection was demonstrated for the rapid determination of molecular weights of proteins. The method employs a capillary array where different uncoated capillaries are filled with gel buffers containing different concentrations of poly(ethylene oxide) (PEO). All data required to construct Ferguson plots and universal calibration curves for the determination of the molecular weights of diverse types of proteins are generated simultaneously in an eight-capillary array within 20 min.

Rational approach to quantitative sodium dodecyl sulfate capillary gel electrophoresis of monoclonal antibodies

Sodium dodecyl sulfate capillary gel electrophoresis has been used to separate and quantify murine monoclonal antibodies. The method uses a murine IgG, whose subclass differs from the analyte antibody, as an internal reference. The internal reference is chosen based on knowing that mouse IgG1 can be separated from mouse IgG2a or IgG2b. Good intra- and inter-day reproducibility [relative standard deviation (RSD)<2%] of peak-area ratio has been obtained. A calibration curve also demonstrates high linearity (R2=0.9999) of response for the analyte. The described method is highly suitable for accurate determination of the antibody concentration even if a capillary electrophoresis apparatus is unable to provide good injection reproducibility.

On-line concentration and separation of proteins by capillary electrophoresis using polymer solutions

Proteins were separated in 0.6% poly(ethylene oxide) (PEO) solutions using a capillary filled with buffers prior to analysis and were detected by laser-induced native fluorescence using a pulsed Nd:YAG laser. PEO solutions entered the capillary by electroosmotic flow (EOF) during the separation. The composition and concentration of the buffer affected the adsorption of PEO molecules on the capillary surface and, consequently caused changes in the EOF. Short separation times (< 7 min) were achieved on a sample solution of five proteins in a 0.6% PEO solution containing 5 microg/mL ethidium bromide using a capillary pre-filled with 100 mM TRIS-borate (TB) buffers (pH 10,0). We also extended this method for on-line concentration and separation of proteins. Proteins dissolved in low-conductivity media stacked in both TB buffers and in PEO solutions. The peak height was proportional to the injection volume up to 2.1 microL using an 80-cm capillary filled with 400 mM TB buffers. Using large injection volumes (2.1 microL), we achieved a limit of detection (S/N = 3) of 31 pM for carbonic anhydrase, which was a 1696-fold sensitivity enhancement compared to a conventional injection method (1 kV for 10 s). In high-conductivity media (urine matrix), stacking occurred at the boundary between the sample zone and PEO solutions. A urine sample without any pretreatment was analyzed, and after stacking, several peaks were detected. Spiking the urine sample with human serum albumin (HSA) affected the fluorescent intensity of some analytes as a result of interaction with HSA.

High-performance sodium dodecyl sulfate-capillary gel electrophoresis of antibodies and antibody fragments

High-performance sodium dodecyl sulfate-capillary gel electrophoresis (SDS-CGE) has been used to separate antibodies and their fragments according to size. Under non-reduced conditions, murine monoclonal antibodies generally show a predominant peak with five to six apparent fragment peaks. The magnitude of the apparent fragmentation is temperature-dependent and is more pronounced with rabbit, sheep and bovine immunoglobulin G's than murine monoclonal antibodies. In addition to temperature, pH and buffer also affect the fragmentation. Without heat treatment during the preparation of the SDS-antibody complexes, the observed fragments become nearly absent; however, some murine monoclonal antibodies exhibit several peaks that group near the expected migration time of an immunoglobulin G, presumably due to their anomalous interaction with sodium dodecyl sulfate. The method can also be used to monitor the progress of peptic digestions to generate murine F(ab')(2) antibody, to perform "gel-shift" assays, and to separate mouse ascitic fluid. This high-performance electrophoretic technique is suitable for quality control as well as the characterization of the antibodies under experimental conditions.

Sodium dodecyl sulfate-capillary electrophoresis of proteins in a sieving matrix utilizing two-spectral channel laser-induced fluorescence detection

We report a method for protein labeling, separation by capillary electrophoresis in a polymer sieving matrix, and detection by laser-induced fluorescence. Different dyes are used to label standard and sample proteins. A two-spectral channel detector resolves fluorescence from the sample and standards. Comparison of the migration time of the sample and standards permits the precise determination of molecular weight, irrespective of variations in run-to-run migration times.

Identifying human platelet glycoproteins IIb and IIIa by capillary electrophoresis

Glanzmann thrombasthenia (GT) is an inherited hemorrhagic defect due to a failure of the platelet membrane glycoprotein (GP) IIb-IIIa complex. Capillary electrophoresis (CE) analysis of solubilized platelet membranes from normal individuals showed the presence of two peaks with a migration time of 27 and 29 min, respectively. An excellent run-to-run and day-to-day reproducibility of the technique (< 1% variation of the retention time) was documented. Using an automated Ferguson method, the apparent molecular masses were 100.0 kDa and 138.5 kDa, respectively. Immunoprecipitation with monoclonal antibodies anti-GP IIIa (B59.2.1) and anti-IIb (61.9.1.3) showed the two peaks as IIIa and IIb, respectively. Electropherograms of a GT young man showed the lack of both peaks. Less than 50% of each peak was present in his parents. Polyacrylamide gel electrophoresis (PAGE), immunoblotting, and flow cytometry analyses showed that GP IIb and IIIa were undetectable in the platelet membranes from the propositus, half of the normal amount being present in both parents. These findings indicate CE to be a rapid, sensitive and reliable tool to investigate patients with abnormalities of the GP IIb-IIIa complex.

Capillary zone electrophoresis of proteins

This review article with 237 references is focused on capillary zone electrophoresis (CZE) of proteins. It includes discussion of modeling electrophoretic migration of proteins, sample pretreatment before the analysis, methods reducing the sorptions of proteins on the capillary wall, and techniques for increasing selectivity by using electrolyte additives including the sieving matrices. Significant progress in detection techniques, namely in laser-induced fluorescence and mass spectrometry, is emphasized. Modifications of CZE using specific interactions, such as affinity capillary electrophoresis or capillary immunoelectrophoresis, are debated as well as combination of CZE with other separation methods such as high performance liquid chromatography (HPLC). A number of practical applications of CZE of proteins are described.

Buffer additives other than the surfactant sodium dodecyl sulfate for protein separations by capillary electrophoresis

The different compounds utilized as additives to the electrolyte solutions employed in protein capillary zone electrophoresis (CZE) for minimizing protein-capillary wall interactions, for improving selectivity and resolution and for controlling the electroosmotic flow are reviewed. The dependence of the electroosmotic flow on the different variables that can be affected by the incorporation of an additive into the electrolytic solution is discussed. A list of the most effective additives employed for protein separations by CZE is reported in Appendix A.

The use of coated and uncoated capillaries for the electrophoretic separation of DNA in dilute polymer solutions

We show that both uncoated and polyacrylamide-coated capillaries provide separation of large DNA restriction fragments (2.0-23.1 kbp) by capillary electrophoresis in dilute cellulosic polymer solutions. Uncoated capillaries, however, provide significantly better resolution of DNA fragments, particularly when ultra-dilute polymer solutions are used. This is because electroosmotic flow in uncoated capillaries increases the residence time of DNA in the capillary, without significantly contributing to band-broadening. At a given field strength and polymer concentration in the buffer, the electrophoretic mobilities of DNA restriction fragments in coated capillaries are virtually identical to those previously measured in uncoated capillaries. It is concluded that the fused silica surface of the capillary does not play a significant role in the mechanism of DNA separation by capillary electrophoresis in uncrosslinked polymer solutions. Thus, the separation of large DNA which has been observed to occur in ultra-dilute polymer solutions arises primarily from entanglement interactions between the cellulosic polymers and DNA restriction fragments which occur within the bulk of the polymer solution.