Binding of purified envelope glycoprotein (gp69/71) of Rauscher murine type-C oncovirus to cellular membrane receptors has been analyzed with reaction systems using intact cells or membranes of disrupted cells. The reaction was highly specific; only cells permissive to infection by Rauscher virus bound the 125I-labeled viral glycoprotein. The specificity of binding was also demonstrated with respect to virus interference; cells productively infected with murine ecotropic type-C virus failed to bind the virus envelope glycoprotein whereas permissive cells infected with murine xenotropic virus continued to bind the Rauscher ecotropic virus glycoprotein. The reaction required the presence of Ca+2, and was rapid and reversible with an equilibrium constant of about 8.3 × 109 m-1 and an association rate constant of about 6.0 × 105 m-1s-1 at 24 °C. The cellular receptors were saturated by about 4 × 105 molecules of glycoprotein per NIH 3T3 cell. No degradation or modification of bound glycoprotein was detected. The binding activity of the purified glycoprotein was susceptible to treatment with urea or guanidine-HCl; modification of tyrosyl, histidyl or tryptophan residues or the reduction of disulfide bonds also blocked the reaction. Sialic acid of the glycoprotein appeared not to be required. The receptor activity of a crude membrane fraction of disrupted cells was abolished by treatment with trypsin, α-chymotrypsin, or phospholipase C.
ASJC Scopus subject areas
- Molecular Biology