The present invention relates to a cell-free enzyme-catalyzed process for producing glycoproteins of general formula (I) from a lipid-linked oligosaccharide and a peptide. Further, said process includes the construction of the lipid-linked oligosaccharide from a mannose trisaccharide containing core structure. Particularly, the lipid-linked oligosaccharide is a high mannose-, complex-, or hybrid-type N-glycan.

The present disclosure relates to the production of oligosaccharides, especially Human milk Oligosaccharides (HMOs) using a genetically engineered cell which has decreased or total loss of function of phosphoglycerol transferase I and II and/or phosphoethanolamine transferase and/or glucans biosynthesis protein C to reduce oligosaccharide by-products and/or increase oligosaccharide production.