systems can differ from glycans produced in humans, as they can be capped with both N-glycolylneuraminic acid (Neu5Gc) and N-acetylneuraminic acid (Neu5Ac), whereas human cells only produce glycoproteins containing N-acetylneuraminic acid. Furthermore, animal cells can also produce glycoproteins containing the galactose-alpha-1,3-galactose epitope, which can induce serious allergenic reactions, including anaphylactic shock, in people who have Alpha-gal allergy. These drawbacks have been addressed by several approaches such as eliminating the pathways that produce these glycan structures through genetic knockouts. Furthermore, other expression systems have been genetically engineered to produce therapeutic glycoproteins with human-like N-linked glycans. These include yeasts such as Pichia pastoris, insect cell lines, green plants, and even bacteria. See also Glycosylation O-linked glycosylation Gene expression N-Glycosyltransferase References External links GlycoEP: In silico Platform for Prediction of N-, O- and C-Glycosites in Eukaryotic Protein Sequences Organic chemistry Biochemistry