The genetic disease AAT deficiency (AATD) is caused by a lack of Alpha-1-antitrypisn (AAT) in the body as a result of causes a number of complications ranging from chronic obstructive pulmonary disease to liver cirrhosis. Augmentation therapy of severe AATD sufferers involves human serum plasma AAT. Unfortunately, this treatment is expensive so a means of reducing the costs and improving the treatments efficiency are of significant interest. The half-life of alpha-1-antitrypsin is increased in vivo markedly by increasing the level of sialylation. Here we describe how the unique disialylgalactose sialylation (DSG) activity of a-2,6-sialyltransferase from Photobacterium Damselae. This disialylgalactose epitope is a unique a2,3 and a2,6 sialic acid sialylation of free end galactose residues. DSG can be used in tandem with CHO produced alpha-1-antitrypsin to markedly increase sialylation. We used numerous glycomic and glycoproteomic techniques such as permethylation, ethyl esterification together with MS methods such as glycomic methods to such as MALDI-MS, Orbitrap-MS and ion-mobility mass spectrometry (IM-MS) to characterise the unique DSG epitope and identify the N-Glycans that contain the previously uncharacterised disialylgalactose motif. This is also the first example of producing the unique disialylgalactose sialylation on a CHO produced biotherapeutic glycoprotein.