[Application of membrane protein-based two-dimensional electrophoresis in chondrocyte- related investigations].

OBJECTIVE: To explore the feasibility of membrane protein-based two-dimensional electrophoresis (2-DE) in the investigations of chondrocyte-related diseases and its complementarity with total protein-based 2-DE. METHODS: Knee cartilage samples were obtained to isolate the chondrocytes with type II collagenase/hyaluronidase digestion. The membrane proteins and total proteins were extracted and loaded separately onto PH3.0-10.0 non-linear gel strip for 2-DE analysis. The qualities of membrane protein-based 2-DE gels were evaluated, and the difference between the distribution profiles of the membrane protein spots and that of the total protein were observed and their complementarities were evaluated. RESULTS: Membrane protein-based 2-DE generated high-quality gel images, and on each gel 412.3±13.5 protein spots were identified. These spots were distributed in the region of isoelectric point pH 5.0-9.0. In the gel images generated by the total proteins, 564.3±5.9 protein spots were identified in each image, and the spots were distributed in the region of isoelectric point pH 3.0-7.0. CONCLUSION: Membrane protein-based 2-DE of the chondrocytes can generate high-quality gel images, and the isoelectric distribution of the protein spots is complementary to that of total protein, which provides valuable information for chondrocyte-related diseases.

[Differential expressed proteins of knee osteoarthritic chondrocytes].

OBJECTIVE: To investigate the molecular mechanism of osteoarthritis (OA) through the differential expressed proteins of advanced osteoarthritic chondrocytes. METHODS: Normal articular cartilage (NAC, n = 22) were obtained from knee cartilage of donors without knee diseases and osteoarthritic cartilage (OAC, n = 17) from OA patients undergoing knee arthroplasty. Total protein was extracted from chondrocytes and loaded directly for two-dimensional gel electrophoresis (2-DE). Gel images were analyzed with the software Imagemaster 2-D platinum3.0 to screen the differential expression protein spots. Target spots were excised and digested and the resulting peptides submitted for mass spectrometry analysis. Identities of differential expressed proteins were recognized through matching the peptide mass finger printing of each spot with NCBI protein database by MASCOT. RESULTS: About 1000 protein spots were presented in the 2-DE gels for each group. Thirty-five NAC spots and 31 OAC spots were confirmed to be differential expression protein spots. Among these spots, 19 proteins were identified by MASCOT, including type VI collagen, enzymes involved in collagen synthesis, shock related proteins and some novel proteins with unknown functions. CONCLUSION: The differential expressed proteins isolated and identified by the present study provide valuable information on various aspects of OA pathology. It may help us to gain new insights into the molecular mechanism of OA.

Tomato LeAGP-1 is a plasma membrane-bound, glycosylphosphatidylinositol-anchored arabinogalactan-protein.

Arabinogalactan-proteins (AGPs) are a class of highly glycosylated, hydroxyproline-rich glycoproteins that function in plant growth and development. Tomato LeAGP-1 represents a major AGP expressed in cultured cells and plants. Based on cDNA and amino acid sequence analyses along with carbohydrate and other biochemical analyses, tomato LeAGP-1 is hypothesized to be a classical AGP localized to the plasma membrane via a glycosylphosphatidylinositol (GPI) anchor. Here, this hypothesis was tested and supported with the following experiments. First, tomato (Lycopersicon esculentum, cv. UC82B) cotyledon protoplasts were isolated following cell wall digestion with cellulase and pectinase, and LeAGP-1 was immunolocalized to the plasma membrane with a LeAGP-1 antibody. Second, LeAGP-1 was shown to be a major AGP component in plasma membrane vesicles from tomato cv. Bonnie Best suspension-cultured cells by Western blot analysis with the LeAGP-1 antibody. Third, fluorescence microscopy of plasmolysed, transgenic tobacco (Nicotiana tabacum BY-2) suspension-cultured cells expressing a green fluorescent protein (GFP)-LeAGP-1 fusion product demonstrated localization to the plasma membrane and Hechtian threads. Fourth, the GFP-LeAGP-1 fusion protein was present in plasma membrane preparations from these transgenic tobacco cells by Western blot analysis with a GFP antibody. Fifth, GFP-LeAGP-1 secreted into the culture media contained ethanolamine, presumably attached to the C-terminal amino acid residue, consistent with its processing and release from the plasma membrane. Thus, these data support the hypothesis that LeAGP-1 is localized to the plasma membrane via a GPI anchor and suggest possible roles for LeAGP-1 in cellular signalling and matrix remodelling.

Tomato LeAGP-1 arabinogalactan-protein purified from transgenic tobacco corroborates the Hyp contiguity hypothesis.

Functional analysis of the hyperglycosylated arabinogalactan-proteins (AGPs) attempts to relate biological roles to the molecular properties that result largely from O-Hyp glycosylation putatively coded by the primary sequence. The Hyp contiguity hypothesis predicts contiguous Hyp residues as attachment sites for arabino-oligosaccharides (arabinosides) and clustered, non-contiguous Hyp residues as arabinogalactan polysaccharide sites. Although earlier tests of naturally occurring hydroxyproline-rich glycoproteins (HRGPs) and HRGPs designed by synthetic genes were consistent with a sequence-driven code, the predictive value of the hypothesis starting from the DNA sequences of known AGPs remained untested due to difficulties in purifying a single AGP for analysis. However, expression in tobacco (Nicotiana tabacum) of the major tomato (Lycopersicon esculentum) AGP, LeAGP-1, as an enhanced green fluorescent protein fusion glycoprotein (EGFP)-LeAGP-1, increased its hydrophobicity sufficiently for chromatographic purification from other closely related endogenous AGPs. We also designed and purified two variants of LeAGP-1 for future functional analysis: one lacking the putative glycosylphosphatidylinositol (GPI)-anchor signal sequence; the other lacking a 12-residue internal lysine-rich region. Fluorescence microscopy of plasmolysed cells confirmed the location of LeAGP-1 at the plasma membrane outer surface and in Hechtian threads. Hyp glycoside profiles of the fusion glycoproteins gave ratios of Hyp-polysaccharides to Hyp-arabinosides plus non-glycosylated Hyp consistent with those predicted from DNA sequences by the Hyp contiguity hypothesis. These results demonstrate a route to the purification of AGPs and the use of the Hyp contiguity hypothesis for predicting the Hyp O-glycosylation profile of an HRGP from its DNA sequence.