In Vitro Sialylation of Recombinant Alpha-1-Antitrypsin using α2,6 Sialyltransferase from Photobacterium Damselae Produces Di-sialyl Galactose Motifs in N-Glycans

Sialic acids are cell surface sugars present in many animal glycoproteins and are of particular interest in biopharmaceuticals, where lack of sialylation can reduce bioactivity. Here we describe how α-2,6-sialyltransferase from Photobacterium Damselae can be used to markedly increase sialylation of CHO produced alpha-1-antitrypsin. Detailed analysis of the sialylation products showed that in addition to the expected α-2,6-sialylation of galactose, a second di-sialyl galactose motif was produced, which had never been recorded on a mammalian glycoprotein. The influence of this unique di-sialylation on the in vitro activity of alpha-1-antitrypsin was studied and a toolkit of mass spectrometry methods to identify this new di-sialyl galactose motif in complex mixtures was developed