Cy5 total protein normalization in Western blot analysis.

Western blotting is a widely used method for analyzing specific target proteins in complex protein samples. Housekeeping proteins are often used for normalization to correct for uneven sample loads, but these require careful validation since expression levels may vary with cell type and treatment. We present a new, more reliable method for normalization using Cy5-prelabeled total protein as a loading control. We used a prelabeling protocol based on Cy5 N-hydroxysuccinimide ester labeling that produces a linear signal response. We obtained a low coefficient of variation (CV) of 7% between the ratio of extracellular signal-regulated kinase (ERK1/2) target to Cy5 total protein control signals over the whole loading range from 2.5 to 20.0µg of Chinese hamster ovary cell lysate protein. Corresponding experiments using actin or tubulin as controls for normalization resulted in CVs of 13 and 18%, respectively. Glyceraldehyde-3-phosphate dehydrogenase did not produce a proportional signal and was not suitable for normalization in these cells. A comparison of ERK1/2 signals from labeled and unlabeled samples showed that Cy5 prelabeling did not affect antibody binding. By using total protein normalization we analyzed PP2A and Smad2/3 levels with high confidence.

Pre-labeling of diverse protein samples with a fixed amount of Cy5 for sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis.

A pre-labeling protocol based on Cy5 N-hydroxysuccinimide (NHS) ester labeling of proteins has been developed for one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. We show that a fixed amount of sulfonated Cy5 can be used in the labeling reaction to label proteins over a broad concentration range-more than three orders of magnitude. The optimal amount of Cy5 was found to be 50 to 250pmol in 20µl using a Tris-HCl labeling buffer at pH 8.7. Labeling protein samples with a fixed amount of dye in this range balances the requirements of sub-nanogram detection sensitivity and low dye-to-protein (D/P) ratios for SDS-PAGE. Simulations of the labeling reaction reproduced experimental observations of both labeling kinetics and D/P ratios. Two-dimensional electrophoresis was used to examine the labeling of proteins in a cell lysate using both sulfonated and non-sulfonated Cy5. For both types of Cy5, we observed efficient labeling across a broad range of molecular weights and isoelectric points.

A quantitative proteomic analysis of soluble bronchoalveolar fluid proteins from patients with sarcoidosis and chronic beryllium disease.

BACKGROUND: Sarcoidosis and chronic beryllium disease (CBD) are granulomatous disorders which can lead to development of chronic inflammation and fibrosis. These diseases have several similarities from their clinical aspects. The aim of this study was to compare the protein profile at the site of active inflammation i.e. the lungs of patients with sarcoidosis and CBD. METHODS: Bronchoalveolar lavage (BAL) proteins from patients having sarcoidosis or CBD were studied using two dimensional gel based proteomics. In this study, we used Difference Gel Electrophoresis (DIGE) proteomics approach to analyse the protein expression profiles from sarcoidosis patients (n=4), CBD (n=4) and healthy controls (n = 5). Subsequently, differentially expressed proteins were identified by using mass spectrometry. RESULTS: We found 37 protein-spots with statistically different expression levels, and identified 14 of these proteins. The protein expression levels of peroxiredoxin 5, heat shock protein 70, complement C3, annexin A2 and transthyretin were significantly different in sarcoidosis versus control group. The proteins; hemopexin, beta2-microglobulin, alpha-1 antitrypsin, cystatin B, IgG kappa chain, apolipoprotein A1, and albumin were significantly different between CBD versus control group. When comparing CBD versus sarcoidosis, we found superoxide dismutase and hemoglobin upregulated in the CBD group. CONCLUSION: By using quantitative proteomics, we were able to find proteins with different expression levels in both diseases.

A simplified 2-D electrophoresis protocol with the aid of an organic disulfide.

2-DE is still a relatively cumbersome and labor intensive method. Given the successful cysteinyl protection concept with hydroxyethyl disulfide (specific oxidation) during the first dimension separation, the possibility for a simplified equilibration procedure was investigated. This was achieved by maintaining the S-mercaptoethanol modified cysteinyls throughout the 2-D workflow including second dimension separation, spot handling, protein digestion, and protein identification. The traditional equilibration protocol encompassing thiol reduction and alkylation was compared with a one-step protocol employing continuous exposure to hydroxyethyl disulfide. Both equilibration protocols gave equally well-resolved spot maps with analytical protein loads regardless of IPG strip pH range. Using preparative protein loads, narrow range IPG strips gave comparable results for the two protocols while preparative load on wide range IPG strips was the only condition where classical reduction/alkylation outperformed hydroxyethyl disulfide equilibration. Moreover, with analytical protein loads, the hydroxyethyl disulfide equilibration time could be significantly reduced without apparent loss of spot map quality or quantitative protein transfer from the first- to the second dimension gel. MALDI-TOF mass spectrometric protein identification was successfully performed with either iodoacetamide or hydroxyethyl disulfide as the cysteine modifier, yielding comparable identification results with high confidence in protein assignment, sequence coverage, and detection of cysteine-containing peptides. The results provide a novel and simplified protocol for 2-DE where the concept of hydroxyethyl disulfide as the cysteinyl protecting agent is extended to cover the entire 2-D work flow.