Monoclonal antibodies as probes to detect conformational changes in the rat cysteine proteinase inhibitor cystatin A

Purification and identification of a protease inhibitor from glassfish (Liparis tanakai) eggs

Two protease inhibitors of 67 and 18 kDa, respectively, were purified from glassfish, Liparis tanakai, eggs by affinity chromatography. The smaller protein was purified with a yield and purity of 0.25% and 49.69-fold, respectively, and was characterized for further study. The glassfish egg protease inhibitor exhibited stability between 50 and 65 degrees C in an alkaline environment (pH 8). It was shown to be a noncompetitive inhibitor against papain, with an inhibitor constant (Ki) of 4.44 nM. Potent glassfish protease inhibitor with N-Val-Gly Ser-Met-Thr-Gly-Gly-Phe-Thr-Asp-C amino acid residues was synthesized and its inhibitory activity was compared. Moreover, the 18-kDa protein inhibited cathepsin, a cysteine protease, more effectively than did egg white protease inhibitor, whereas the reverse was true for papain. Glassfish egg protease inhibitor is classified as a member of the family I cystatins.

Changes in expression of monoclonal antibody epitopes on laminin-5r induced by cell contact

Laminin-5r is a basement membrane component that promotes rapid adhesion and hemidesmosome formation in epithelial cells. We raised monoclonal antibodies and identified their corresponding epitopes on the constituent chains of laminin-5r by western blotting. Using a combination of immunoprecipitation and ELISA assays, we determined that these epitopes are differentially exposed on two forms of the laminin-5r heterotrimer: soluble (passively adsorbed onto plastic) and cell-associated. Antibody 5C5 epitope is exposed on the cell-associated form, but not the soluble/passively adsorbed form of laminin-5r. Epitopes reactive with antibodies CM6, FM3, and TR1 are also preferentially exposed on cell-associated laminin-5r, such that reactivity of these antibodies with the cell-associated form is fourfold higher than with the soluble/passively adsorbed form in ELISA assays. Incubation of passively adsorbed laminin-5r with the human epithelial cell line SCC12 induced exposure of 5C5 and CM6, FM3, or TR1 epitopes. These data suggest that cells actively modify laminin-5r, perhaps during matrix assembly, and that the 5C5 epitope may serve as a marker for assembled laminin-5r matrix.