FIG. 1.

An 80-kDa cell surface protein binds to the pre-S1 domain of the GST–pre-S1 fusion protein. Cultured human hepatocytes (A) and HepG2 cells (B) were biotinylated. The cell lysates were incubated with GST and further incubated with glutathione-Sepharose beads. After the Sepharose beads were extensively washed with lysis buffer, the bound proteins were eluted by heating to 100°C for 5 min, subjected to SDS-PAGE (10% gel) and Western analysis using streptavidin-HRP conjugate, and visualized by ECL (lane 1). The unbound proteins (precleared lysate) were incubated with GST–pre-S1 fusion protein followed by glutathione-Sepharose beads. The bound proteins were then analyzed as described above (lane 2). As a negative control, cell lysates of unbiotinylated human hepatocyte were incubated with GST (lane 3) or GST–pre-S1 (lane 4) and then analyzed as described above. Molecular size markers (M; in kilodaltons) are shown on the left, and the position of p80 is indicated on the right.