Binding specificity and mobility in SDS-PAGE gel of the full-length native TCblR and the recombinant extracellular domain. (A) Binding of TC-Cbl to detergent soluble full-length TCblR purified from placental membranes and (B) to the recombinant extracellular fragment lacking the transmembrane and cytoplasmic domains produced as a secretory protein in mammalian cells. [⁵⁷Co]Cbl-TC (0.015-1.2 pmol) was incubated with 0.1 pmol of TCblR for 1 hour at room temperature, and the [⁵⁷Co]Cbl-TC-receptor complex formed was captured on 50 μL of WGA agarose by mixing for an additional 1 hour at 4°C. (C) Western blot of TCblR separated in a reducing 8% SDS-PAGE gel. The protein was visualized by incubating with a polyclonal antiserum to the extracellular fragment of TCblR followed by peroxide conjugated secondary antibody. Lane 1, native TCblR purified from human placental membranes; lane 2, the recombinant extracellular domain expressed in mammalian cells.