Specific association of retroviral envelope protein, p15E, with human cell surfaces

Experiments were carried out to analyze the binding sites on human cells for highly purified retroviral protein p15E isolated from Feline Leukemia Virus, Rickard Strain. Binding of 125I-labeled p15E was tested with surfaces of human peripheral blood lymphocytes and 3 cell lines, Raji, MOLT-4, and U-937. 125I-labeled p15E showed specific binding to human peripheral blood lymphocytes. In addition, all of the cell lines tested showed binding of 125I-labeled p15E. Using U-937 cells, we characterized the interaction between p15E and the surface of these cells, and showed that the binding was specific by the following 3 different sets of evidence: (i) in equilibrium binding experiments, 18,000 binding sites with a dissociation constant of 2 x 10(-9) M were present on U-937 cells; (ii) trypsin or N-glycanase treatment decreased the binding sites of 125I-labeled p15E; and (iii) by affinity chromatography using p15E or BSA Sepharose columns, the isolated membranes of 125I-labeled U-937 cells previously treated with Triton X-100 showed a significantly higher binding to the p15E column than to the BSA column.