Site-specific glycosylation of an aglycosylated human IgG1-Fc antibody protein generates neoglycoproteins with enhanced function

Abstract

A range of well-defined IgG glycoforms was prepared by employing a combination of synthetic carbohydrate chemistry and genetic engineering. The key aspect of this methodology is the coupling of thioaldoses with cysteine-containing proteins to give disulfide-linked neoglycoproteins. This technology was applied to the synthesis of a series of synthetic N-glycan thioaldoses which were coupled to an aglycosylated IgG1-Fc fragment, engineered to have Cys-297 in place of glycan-linked Asn (Δh-Fc N297C). Analysis of the resulting Fc neoglycoproteins by mass spectrometry and trypsin digestion showed that the saccharides were site-selectively incorporated at Cys-297 to full occupancy without affecting other Fc protein disulfides. The neoglycoproteins were tested for their ability to interact with human FcγRI by inhibiting superoxide production by γ -interferon-stimulated U937 cells. The neoglycoproteins displayed enhanced superoxide inhibition relative to aglycosylated Δh-Fc N297C, where increased glycan size correlated positively with increased inhibition.