Synthesis of neoglycoconjugates containing deaminated neuraminic acid (KDN) using rat liver α2,6-sialyltransferase

2-Keto-3-deoxy-D-glycero-D-galacto-nononic acid (KDN) was introduced into asialotransferrin and N-acetyllactosamine (LacNAc) from CMP-KDN by using rat liver Gal beta 1-->4GlcNAc alpha 2,6-sialyltransferase to form KDN-transferrin and KDN-LacNAc. These structures contain terminal KDN alpha 2-->6Gal-residues, a glycotope that has not yet been described in natural glycoconjugates. KDN was transferred to all four Gal residues in asialotransferrin by this enzyme. The incorporation efficiency of KDN from CMP-KDN into asialotransferrin was about half that of Neu5Ac from CMP-Neu5Ac, based on the V-max/K-m values for these donor substrates, 0.0527 min(-1) and 0.119 min(-1), respectively. The KDN alpha 2-->6Gal linkage was resistant to exosialidase treatment, in contrast to the sensitivity of the Neu5Ac alpha 2-->6Gal linkage. Interestingly, Sambucus sieboldiana agglutinin (SSA) was shown to prefer KDN-transferrin to the corresponding Neu5Ac-transferrin, as estimated by slot-blot analysis. The use of an alpha 2,6-sialyltransferase to synthesize neoglycoproteins containing KDN has not been previously reported. Their facile synthesis using CMP-KDN and sialyltransferases with different specificities offers new possibilities to study the function of neo-KDN-glycoconjugates, and to explore their use in glycotechnology.