Binding of Unglycosylated and Glycosylated Human Recombinant Interferon-γ to Cellular Receptors

Abstract

Recombinant human interferons (IFNs), either unglycosylated produced in E. coli (rIFN-γ) or glycosylated produced in CHO cells (g-rIFN-γ), were labeled with ¹²⁵I to similar specific activities to study their interaction with cell-surface receptors. When analyzed by gel electrophoresis, rIFN-γ run as a single polypeptide of M_r 15,000-17,000, whereas g-rIFN-γ separated into three components of M_r 20,000, 22,000, and 43,000, which corresponded to the known size of the two monomeric and one dimeric forms of glycosylated natural IFN-γ. The binding of the two species of ¹²⁵I-IFN-γ was competed equally by rIFN-γ in competition displacement experiments with Daudi cells, indicating that these IFNs bind with similar high affinity to the same receptors. K _D values of 1.25 × 10^-10 and 2.5 × 10^-10 M were determined for g-rIFN-γ and rIFN-γ, respectively. This relatively small difference in K _D does not apparently result in a detectable difference in biological activity, as measured by the increase in 2′,5′-oligo(A) synthetase activity in IFN-treated HeLa and A549 cells. These results indicate that glycosylation of IFN-γ does not play a significant role in its interaction with cellular receptors and in the induction of a biological response.