The glycosylation of alpha-1-antitrypsin expressed in transgenic mice

Alpha-l-Antitrypsin (AAT) is a serine protease inhibitor whose main physiological role is the control of neutrophil elastase. In AAT deficiency disorders, mutants are poorly secreted or have low stability leading to emphysema and liver disease. AAT has three N-linked glycosylation sites; the unglycosylated protein is fully active but has a much reduced half-life in the circulation. Therefore, for therapeutic use large quantities of fully glycosylated AAT are required. Transgenic animals that express human AAT in mammary tissue have the potential to be used as bioreactors. Their ability to glycosylate the recombinant protein is crucial. AAT has been purified from human plasma and transgenic mouse milk, the glycopeptides isolated and the glycosylation microheterogeneity characterised. The major N-glycans identified from recombinant human AAT purified from transgenic mouse milli and from human plasma were complex sialylated biantennary structures. However, individual mice showed variation in site occupancy, the degree of fucosylation and the range of minor N-glycan structures detected.