Structural characterization of polypeptides and proteins by combination of capillary electrophoresis and (252)Cf plasma desorption mass spectrometry

Capillary electrophoretic analysis of mu- and m-calpain using fluorescently labeled casein substrates

Calpains are unique calcium-dependent thiol proteases that have been proposed to participate in a number of physiological processes including signal transduction and protein turnover in skeletal muscle. Calpains exist in two major forms. Interestingly, the two forms of protease show no significant difference in their action on various substrates. The only demonstrable difference in their activity involves the concentration of calcium required for activation. Both mu- and m-calpains typically achieve half maximal activation at 50 microM and 0.7 mM calcium, respectively. The focus of this study was to examine the action of both forms of calpain on casein substrates and assess whether any differences could be observed in the resulting peptide finger print using capillary electrophoresis. Purified mu- and m-calpain were incubated for various lengths of time with Oregon Green labeled alphas- and beta-casein. The reactions were stopped with sodium dodecyl sulfate (SDS) and products separated by capillary electrophoresis in micellar electrokinetic capillary chromatography (MEKC) mode using laser-induced fluorescence (LIF) detection. Comparison of the electropherograms showed no difference in the peptide profile for either enzyme. However, it was found that beta-casein was hydrolyzed more extensively than alphas-casein, by both enzymes. Capillary electrophoresis was found to be a very sensitive technique for detection of calpain activity. Using beta-casein as substrate, the CE approach was able to detect 2-3 ng of calpain activity. The results also suggest that capillary electrophoresis is a useful tool for proteolytic investigations of protein structure.

Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications

This review is in support of the development of selective, reproducible and validated capillary electrophoretis (CE) methods. Focusing on pharmaceutical and biological applications, the successful use of CE is demonstrated by more than 800 references, mainly from 1994 until 1998. Approximately 80 recent reviews have been catalogued. These articles sum up the existing strategies for method development in CE, especially in the search for generally accepted concepts, but also looking for new, promising reagents and ideas. General strategies for method development were derived not only with regard to selectivity and efficiency, but also with regard to precision, short analysis time, limit of detection, sample pretreatment requirements and validation. Standard buffer recipes, surfactants used in micellar electrokinetic capillary chromatography (MEKC), chiral selectors, useful buffer additives, polymeric separation media, electroosmotic flow (EOF) modifiers, dynamic and permanent coatings, actions to deal with complex matrices and aspects of validation are collected in 20 tables. Detailed schemes for the development of MEKC methods and chiral separations, for optimizing separation efficiency, means of troubleshooting, and other important information for key decisions during method development are given in 19 diagrams. Method development for peptide and protein separations, possibilities to influence the EOF and how to stabilize it, as well as indirect detection are considered in special sections.

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.

Isolation of hydrophobic lipoproteins in organic solvents by pressure-assisted capillary electrophoresis for subsequent mass spectrometric characterization

Two capillary electrophoretic (CE) separation techniques with either simultaneous solvent flow induced by hydrostatic pressure or CE followed by low pressurization with helium were developed for the analysis of extremely hydrophobic proteins, such as the lung surfactant protein SP-C. For both related procedures, buffer solutions containing up to 70% of 2-propanol were used for the capillary electrophoretic separation. This high concentration of organic co-solvent, needed to solubilize the protein, dramatically reduces the electroosmotic flow (EOF) in aminopropyltrimethoxysilane-treated fused-silica capillaries. Because the EOF was insufficient to elute the separated analytes from the capillary, two "pressure-assisted" CE techniques were developed. An additional flow to elute the separated analytes was produced either by raising the inlet of the capillary or by helium pressure. Using the pressurization procedure a baseline separation of the SP-C protein and its dimeric complex was obtained in a 55-minute electrophoretic run, followed by pressure elution of the analyte to the detector. The present combination of pressurization and capillary electrophoresis does not require any detergents or involatile buffer additives, which are usually needed to solubilize extremely hydrophobic lipoproteins. It is therefore applicable to on-line coupling with electrospray mass spectrometry for the direct structural characterization of hydrophobic proteins.

Capillary electrophoresis combined with 252Cf plasma desorption and electrospray mass spectrometry for the structural characterization of hydrophobic polypeptides using organic solvents

Capillary electrophoresis (CE) conditions have been developed for the separation of hydrophobic polypeptides, such as fatty acid-acylated peptides, and their subsequent structural identification by 252Cf plasma desorption (PDMS) and electrospray mass spectrometry (ESMS). Salt- and detergent-free aqueous acetic acid buffers containing up to 20% 2-propanol or 25% acetonitrile were employed for CE separations of hydrophobic peptides with (i) untreated, and (ii) 3-aminopropyltrimethoxysilane-derived fused silica capillaries. For both capillary types, electroosmotic flow rates suitable for sample isolation and transfer were determined, and CE separations of polypeptide mixtures were compared for aqueous buffers containing 2-propanol or acetonitrile. For the mass spectrometric identification of CE-separated peptides, a sheath flow sample isolation method was developed for subsequent transfer to PDMS. This procedure enabled the efficient isolation of peptide fractions for PDMS analysis, or alternative microanalytical techniques.