Isolation of a novel cytotoxic lymphokine (factor 2) from a human B-cell line (Karpas 160b) by preparative isoelectric focusing in the rotofor cell and chromatofocusing

New separation tools for comprehensive studies of protein expression by mass spectrometry

Mass spectrometry has emerged as a core technique for protein identification and characterization because of its high sensitivity, accuracy, and speed of analysis. The most widespread strategy for studying global protein expression in biological systems employs analytical two-dimensional polyacrylamide gel electrophoresis (2D PAGE) followed by enzymatic degradation of isolated protein spots, peptide mapping, and bioinformatics searches. Using this method, thousands of proteins can be resolved in a gel and their expression quantified. However, certain types of proteins possessing important cellular functions are not easily analyzed using this strategy. These proteins include membrane, low copy number, highly basic, and very large (> 150 kDa) and small (< 10 kDa) proteins. To meet the growing need to simultaneously monitor all types of proteins in a biological system, new separation strategies have emerged that are amenable to hyphenation to mass spectrometric techniques. This article will review these new techniques and examine their usefulness in studies of protein expression.

Identification of synaptic vesicle, pre- and postsynaptic proteins in human cerebrospinal fluid using liquid-phase isoelectric focusing

Synaptic pathology is central in the pathogenesis of several psychiatric disorders, for example in Alzheimer's disease (AD) and schizophrenia. Quantification of specific synaptic proteins has proved to be a useful method to estimate synapitc density in the brain. Using this approach, several synaptic proteins have been demonstrated to be altered in both AD and schizophrenia. Until recently, the analysis of synaptic pathology has been limited to postmortem tissue. In living subjects, these synaptic proteins may be studied through analysis of cerebrospinal fluid (CSF). In an earlier study performed by us, one synaptic vesicle specific protein, synaptotagmin, was detected in CSF for the first time using a procedure based on affinity chromatography, reversed-phase chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and chemiluminescence immunoblotting. However, other synaptic proteins were not detectable with this procedure. Therefore, we have developed a procedure including precipitation of CSF proteins with trichloroacetic acid, followed by liquid-phase isoelectric focusing using the Rotofor Cell, and finally analysis of Rotofor fractions by Western blotting for identification of synaptic proteins in CSF. Five synaptic proteins, rab3a, synaptotagmin, growth-associated protein (GAP-43), synaptosomal-associated protein (SNAP-25) and neurogranin, have been demonstrated in CSF using this method. The major advantage of liquid-phase isoelectric focusing (IEF) using the Rotofor cell is that it provides synaptic proteins from CSF in sufficient quantities for identification. This method may also be suitable for identification of other types of trace amounts of brain-specific proteins in CSF. These results demonstrate that several synaptic proteins can be identified and measured in CSF to study synaptic function and pathology in degenerative disorders.

Characterization of proteins from human cerebrospinal fluid by a combination of preparative two-dimensional liquid-phase electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

To purify and characterize low-abundance proteins in complex biological mixtures, we used a novel strategy that combined preparative two-dimensional liquid-phase electrophoresis (2D-LPE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Preparative 2D-LPE is based on the same isoelectric focusing and gel electrophoresis principles as the widely used analytical 2D gel electrophoresis, except that analytes remain in solution throughout separation. This novel approach shows many improvements compared to analytical 2D gel electrophoresis for the separation of proteins in biological fluids. For example, larger volumes/amounts of samples can be loaded, yielding sufficient amounts of low-abundance proteins for further characterization. Since proteins remain in liquid phase during the entire procedure, extra steps such as electroelution, extraction, or transfer to membranes from the gels prior to mass spectrometric analysis are obviated. We report the usefulness of 2D-LPE combined with MALDI-TOF MS for the purification and characterization of cystatin C and beta-2 microglobulin in human cerebrospinal fluid. This method should be applicable to a wide range of biological fluids, such as cerebrospinal fluid, serum, tissue extracts, cell media, whole cells, and bacterial lysates.

An antibody reactive with domain 4 of the platelet-derived growth factor beta receptor allows BB binding while inhibiting proliferation by impairing receptor dimerization

A panel of murine monoclonal antibodies was generated against the extracellular domain of the human platelet-derived growth factor (PDGF) beta receptor (PDGFRbeta). These antibodies were assayed for both the ability to inhibit binding of PDGF BB to PDGFRbeta+ cells as well as the capacity to inhibit PDGF BB-mediated mitogenesis. As expected, all antibodies that could prevent PDGF BB binding also inhibited mitogenesis. However one antibody (M4TS.11), with no detectable ability to inhibit PDGF BB binding, was a potent inhibitor of proliferation induced by PDGF BB. Further characterization indicated that M4TS.11 impaired PDGFRbeta dimerization, revealing the mechanism by which it prevented PDGF BB-mediated mitogenesis. Using domain deletion mutants of the extracellular portion of PDGFRbeta, the determinant recognized by this antibody was localized to the fourth extracellular domain of PDGFRbeta, indicating that this domain, which is not involved in ligand binding, actively participates in receptor dimerization and signal transduction. The M4TS.11 antibody could also inhibit PDGF BB-mediated proliferation of responsive cells from both the baboon and the rabbit, indicating the determinant recognized by the antibody is not limited to humans and making it possible to use this antibody to evaluate the therapeutic benefit of interfering with PDGF in animal models of human disease.

Expression of platelet-derived growth factor (PDGF) receptor alpha-subunit in mouse brain: comparison of Patch mutants and normal littermates

1. Platelet-derived growth factor (PDGF) plays an important role not only in mesenchyme-derived tissues, but also in the mammalian central nervous system. The Patch mutant (Ph/+) lacks one copy of the PDGFR-alpha gene. However, it is not clear whether there are differences in expression of PDGF receptor alpha-subunit (PDGFR-alpha) in brain tissue of the Patch heterozygous (Ph/+) mutants compared to wild-type C57Bl (+/+) mice. 2. The level of PDGRF-alpha mRNA expression is slightly lower in Patch mutant than in normal littermate. 3. Protein and total RNA isolated from mouse brain tissue and primary type 1 astrocyte cultures were studied with Western and Northern blotting techniques. There was no measurable difference ir PDGFR-alpha protein expression between the Patch and wild-type mouse nervous system. Adjustment of transcriptional efficiency and messenger stability may contribute to this phenomenon, whose biological significance remains unclear. 4. Further, the expression of PDGRF-alpha protein and message in mouse brain tissues is developmentally regulated. Its level remains high during the embryonic period and declines below measurable levels in adult.

Solute focusing techniques for bioseparations

The growth of industrial biotechnology has had a major impact on the research and development of both analytical and preparative focusing techniques. Pioneering methods such as isoelectric focusing are being modified to overcome the limitations of batch mode operation, scale up difficulties, high power requirement, and excessive heat generation. present advances in focusing techniques have been made by either overcoming the limitations of standard techniques or by investigating new focusing systems. Here we review the background and history of isoelectric focusing and discuss several new focusing techniques including recycle isoelectric (RIEF), counteracting chromatographic electrophoresis (CACE), and countercurrent gradient chromatography (CGC).