Chemoenzymatic synthesis of α2-3-sialylated carbohydrate epitopes

Sialic acids are common terminal carbohydrates on cell surface. Together with internal carbohydrate structures, they play important roles in many physiological and pathological processes. In order to obtain alpha 2-3-sialylated oligosaccharides, a highly efficient one-pot three-enzyme synthetic approach was applied. The P. multocida alpha 2-3-sialyltransferase (PmST1) involved in the synthesis was a multifunctional enzyme with extremely flexible donor and acceptor substrate specificities. Sialyltransferase acceptors, including type 1 structure (Gal beta 1-3GlcNAc beta ProN(3)), type 2 structures (Gal beta 1-4GlcNAc beta ProN(3) and 6-sulfo-Gal beta 1-4GlcNAc beta ProN(3)), type 4 structure (Gal beta 1-3GalNAc beta ProN(3)), type 3 or core 1 structure (Gal beta 1-3GalNAc alpha ProN(3)) and human milk oligoscaccharide or lipooligosaccharide lacto-N-tetraose (LNT) (Gal beta 1-3GlcNAc beta 1-3Gal beta 1-4Glc beta ProN(3)), were chemically synthesized. They were then used in one-pot three-enzyme reactions with sialic acid precursor ManNAc or ManNGc, to synthesize a library of naturally occurring alpha 2-3-linked sialosides with different internal sugar structures. The sialylated oligosaccharides obtained are valuable probes for their biological studies.