Biosynthesis of the IFN-γ binding protein of ectromelia virus, the causative agent of mousepox

Ectromelia virus (ECTV), the causative agent of mousepox, expresses an extracellular interferon-gamma binding protein (IFN-gamma BP) with homology to the ligand binding domains of the IFN-gamma high affinity receptor (IFN-gamma R1). Unlike the cellular receptor, the IFN-gamma BP binds IFN-gamma from several species. The IFN-gamma BP is synthesized early after infection, accumulating in the extracellular milieu as dimers composed of two protein species with M-r of 34.6 or 33.0 kDa. Homodimers are covalently linked by an interchain disulphide bond at position 216. The IFN-gamma BP has complex N-linked oligosaccharides at positions 41 and 149 as determined by site-directed mutagenesis and glycosidase treatment. Glycosylation at position 41 is required for secretion from mammalian cells and may play a role in the activity of the IFN-gamma BP. Glycosylation at position 149 is not required for secretion, and the lack of glycosylation at this site does not diminish ligand binding as measured by surface plasmon resonance (SPR) and ELISA. (c) 2005 Elsevier Inc. All rights reserved.