Molecular modeling of the effects of glycosylation on the structure and dynamics of human interferon-gamma.

Natural hIFNγ is a glycoprotein with two N-glycosylation sites in each monomer chain, which are independently and differentially glycosylated. Although glycosylation is not necessary for the activity of the cytokine, it was proposed that it protects the cytokine from proteolytic degradation and thus extends its circulatory half-life. Here, we report the development of model structures of glycosylated full-length native hIFNγ homodimers. Our aim is to shed light on the mechanism through which glycosylation preserves the integrity of the cytokine molecule. To this end, we employ molecular dynamics simulations to study the interaction of the carbohydrate chains with the receptor-binding sites in the cytokine and with its flexible highly positively charged C-termini. The glycans interact primarily with the globular part of the protein, but also occasionally form contacts with the solvent-exposed and sensitive to proteases C-terminal tails. We show that the glycans restrict the C-termini wagging motion into the solvent, limit their flexibility and keep them closer to the α-helical globule of hIFNγ, thus possibly protecting them from proteolytic processing.