Polar Electrophoresis: Shape of Two-Dimensional Maps Is as Important as Size

The performance of two-dimensional electrophoresis in conventional gels in Cartesian coordinates (2-DE) vs. polar coordinates (2-PE) is here evaluated. Although 2-DE is performed in much longer Immobiline gels in the first dimension (17 cm) vs. barely 7-cm in 2-PE, an equivalent resolving power is found. Moreover, due to the possibility of running up to seven Immobiline strips in the radial gel format, the reproducibility of spot position is seen to be higher, this resulting in a 20% higher matching efficiency. As an extra bonus, strings of “isobaric” spots (i.e. polypeptides of identical mass with different pI values) are more resolved in the radial gel format, especially in the 10 to 30 kDa region, where the gel area fans out leaving extra space for spot resolution. In conclusion, this novel gel format in the second dimension of 2D gels is seen as an important improvement of this technique, still one of the most popular in proteome analysis

High Abundance Proteins Depletion vs Low Abundance Proteins Enrichment: Comparison of Methods to Reduce the Plasma Proteome Complexity

BACKGROUND: To date, the complexity of the plasma proteome exceeds the analytical capacity of conventional approaches to isolate lower abundance proteins that may prove to be informative biomarkers. Only complex multistep separation strategies have been able to detect a substantial number of low abundance proteins (<100 ng/ml). The first step of these protocols is generally the depletion of high abundance proteins by the use of immunoaffinity columns or, alternatively, the enrichment of by the use of solid phase hexapeptides ligand libraries. METHODOLOGY/PRINCIPAL FINDINGS: Here we present a direct comparison of these two approaches. Following either approach, the plasma sample was further fractionated by SCX chromatography and analyzed by RP-LC-MS/MS with a Q-TOF mass spectrometer. The depletion of the 20 most abundant plasma proteins allowed the identification of about 25% more proteins than those detectable following low abundance proteins enrichment. The two datasets are partially overlapping and the identified proteins belong to the same order of magnitude in terms of plasma concentration. CONCLUSIONS/SIGNIFICANCE: Our results show that the two approaches give complementary results. However, the enrichment of low abundance proteins has the great advantage of obtaining much larger amount of material that can be used for further fractionations and analyses and emerges also as a cheaper and technically simpler approach. Collectively, these data indicate that the enrichment approach seems more suitable as the first stage of a complex multi-step fractionation protocol

Texture classification of proteins using support vector machines and bio-inspired metaheuristics

6th International Joint Conference, BIOSTEC 2013, Barcelona, Spain, February 11-14, 2013[Abstract] In this paper, a novel classification method of two-dimensional polyacrylamide gel electrophoresis images is presented. Such a method uses textural features obtained by means of a feature selection process for whose implementation we compare Genetic Algorithms and Particle Swarm Optimization. Then, the selected features, among which the most decisive and representative ones appear to be those related to the second order co-occurrence matrix, are used as inputs for a Support Vector Machine. The accuracy of the proposed method is around 94 %, a statistically better performance than the classification based on the entire feature set. This classification step can be very useful for discarding over-segmented areas after a protein segmentation or identification process

Improvements to polar 2-D electrophoresis for proteomic applications.

Recently, we reported a new way of performing 2-DE, called P-dimensional electrophoresis (2-PE). In this approach, the second dimension is achieved in a radial gel which can accommodate up to six 7 cm long IPG strips simultaneously, improving reproducibility and throughput power in respect to 2-DE. Nevertheless, 2-PE was up to now limited to the use of only short strips because of technical difficulties. Here, we describe how to load longer strips (e.g., 18-24 cm) on 2-PE and report some representative images for a qualitative assessment

Pros and cons of peptide isolectric focusing in shotgun proteomics

In shotgun proteomics, protein mixtures are proteolytically digested before tandem mass spectrometry (MS/MS) analysis. Biological samples are generally characterized by a very high complexity, therefore a step of peptides fractionation before the MS analysis is essential. This passage reduces the sample complexity and increases its compatibility with the sampling performance of the instrument. Among all the existing approaches for peptide fractionation, isoelectric focusing has several peculiarities that are theoretically known but practically rarely exploited by the proteomics community. The main aim of this review is to draw the readers' attention to these unique qualities, which are not accessible with other common approaches, and that represent important tools to increase confidence in the identification of proteins and some post-translational modifications. The general characteristics of different methods to perform peptide isoelectric focusing with natural and artificial pH gradients, the existing instrumentation, and the informatics tools available for isoelectric point calculation are also critically described. Finally, we give some general conclusions on this strategy, underlying its principal limitations

Kinetics of albumin homocysteinylation measured with matrix-assisted laser/desorption ionization mass spectrometry versus with a radioactive tracer.

Abstract: Homocysteinylation is a post-translational protein modification which involves homocysteine-thiolactone and may be responsible for many pathophysiological changes secondary to hyperhomocysteinemia. Therefore, methods to measure protein homocysteinylation in intact biological samples are required. We tested whether matrix assisted-laser/desorption ionization mass spectrometry (MALDI-MS) can detect time- and dose-dependent changes in in vitro homocysteine-thiolactone binding to human serum albumin. We have compared this method with a (35)S-thiolactone radioactive binding assay. Incubations with and without dithiothreitol allowed measurement of the amide-linked and disulfide-linked thiolactone-protein adducts, respectively. A good correspondence in time- and dose-dependent protein-thiolactone formation was observed between the two methods. A maximum of 9 to 12 thiolactone residues were bound to each albumin molecule. The (35)S-thiolactone bound albumin tightly, particularly at the lowest concentrations, with approximate to 70% of the binding amide-linked. Although the results of the two methods were rather similar, the radioactive method appears to be more sensitive than the MALDI-MS technique