Isolation and characterization of [3H]fucose-labeled glycoproteins from the serum of normal rats and rats bearing Zajdela hepatoma

Identification and analysis of altered alpha1,6-fucosylated glycoproteins associated with hepatocellular carcinoma metastasis

Tumor metastasis might be associated with the expression levels of cellular glycoproteins and the alteration of their glycan parts. In order to screen the aberrantly alpha1,6-fucosylated glycoproteins related to hepatocellular carcinoma (HCC) metastasis, a high-throughput glycomic approach which consisted of 2-DE, electronic transfer of proteins, lectin affinity blot and precipitation, and MALDI-TOF-MS/MS, was established. Lens culinaris agglutinin (LCA) affinity glycoprotein profiles of higher and lower metastatic HCC cell lines were compared and analyzed. Seven out of 34 identified glycoproteins were differentially displayed; they were cytokeratin 8 (CK8), annexin I, annexin II, heterogeneous nuclear ribonucleoprotein A/B, PDZ and LIM domain 1, RNA-binding motif protein 4, and poly(rC)-binding protein 1. On comparison with Hep3B, CK8 showed a higher affinity to Ricinus communis agglutinin 1 (RCA-I) and LCA, and annexin I presented a higher affinity to LCA and Con A by the lectin-binding assay. Furthermore, the up-regulation of CK8, annexin I, and annexin II were found by Western blot and immunofluorescence analysis in higher metastatic HCC cell lines. This implied that the alteration of CK8, annexin I, and annexin II both in their expression levels and their glycan parts might be related to metastatic ability, and play a critical role in the process of HCC metastasis.

Functional characterization of two-dimensional gel-separated proteins using sequential staining

Proteins separated by two-dimensional (2-D) gel electrophoresis can be visualized using various protein staining methods. This is followed by downstream procedures, such as image analysis, gel spot cutting, protein digestion, and mass spectrometry (MS), to characterize protein expression profiles within cells, tissues, organisms, or body fluids. Characterizing specific post-translational modifications on proteins using MS of peptide fragments is difficult and labor-intensive. Recently, specific staining methods have been developed and merged into the 2-D gel platform so that not only general protein patterns but also patterns of phosphorylated and glycosylated proteins can be obtained. We used the new Pro-Q Diamond phosphoprotein dye technology for the fluorescent detection of phosphoproteins directly in 2-D gels of mouse leukocyte proteins, and Pro-Q Emerald 488 glycoprotein dye to detect glycoproteins. These two fluorescent stains are compatible with general protein stains, such as SYPRO Ruby stain. We devised a sequential procedure using Pro-Q Diamond (phosphoprotein), followed by Pro-Q Emerald 488 (glycoprotein), followed by SYPRO Ruby stain (general protein stain), and finally silver stain for total protein profile. This multiple staining of the proteins in a single gel provided parallel determination of protein expression and preliminary characterization of post-translational modifications of proteins in individual spots on 2-D gels. Although this method does not provide the same degree of certainty as traditional MS methods of characterizing post-translational modifications, it is much simpler, faster, and does not require sophisticated equipment and expertise in MS.

Detection technologies in proteome analysis

Common strategies employed for general protein detection include organic dye, silver stain, radiolabeling, reverse stain, fluorescent stain, chemiluminescent stain and mass spectrometry-based approaches. Fluorescence-based protein detection methods have recently surpassed conventional technologies such as colloidal Coomassie blue and silver staining in terms of quantitative accuracy, detection sensitivity, and compatibility with modern downstream protein identification and characterization procedures, such as mass spectrometry. Additionally, specific detection methods suitable for revealing protein post-translational modifications have been devised over the years. These include methods for the detection of glycoproteins, phosphoproteins, proteolytic modifications, S-nitrosylation, arginine methylation and ADP-ribosylation. Methods for the detection of a range of reporter enzymes and epitope tags are now available as well, including those for visualizing beta-glucuronidase, beta-galactosidase, oligohistidine tags and green fluorescent protein. Fluorescence-based and mass spectrometry-based methodologies are just beginning to offer unparalleled new capabilities in the field of proteomics through the performance of multiplexed quantitative analysis. The primary objective of differential display proteomics is to increase the information content and throughput of proteomics studies through multiplexed analysis. Currently, three principal approaches to differential display proteomics are being actively pursued, difference gel electrophoresis (DIGE), multiplexed proteomics (MP) and isotope-coded affinity tagging (ICAT). New multiplexing capabilities should greatly enhance the applicability of the two-dimensional gel electrophoresis technique with respect to addressing fundamental questions related to proteome-wide changes in protein expression and post-translational modification.