An Engineered Pathway for Production of Terminally Sialylated -glycoproteins in the Periplasm of

Terminally sialylated -glycoproteins are of great interest in therapeutic applications. Due to the inability of prokaryotes to carry out this post-translational modification, they are currently predominantly produced in eukaryotic host cells. In this study, we report a synthetic pathway to produce a terminally sialylated -glycoprotein in the periplasm of , mimicking the sialylated moiety (Neu5Ac-α-2,6-Gal-β-1,4-GlcNAc-) of human glycans. A sialylated pentasaccharide, Neu5Ac-α-2,6-Gal-β-1,4-GlcNAc-β-1,3-Gal-β-1,3-GlcNAc-, was synthesized through the activity of co-expressed glycosyltransferases LsgCDEF from , NeuBCA enzymes, and α-2,6-sialyltransferase in an engineered strain which produces CMP-Neu5Ac. oligosaccharyltransferase PglB was used to transfer the terminally sialylated glycan onto a glyco-recognition sequence in the tenth type III cell adhesion module of human fibronectin. Sialylation of the target protein was confirmed by lectin blotting and mass spectrometry. This proof-of-concept study demonstrates the successful production of terminally sialylated, homogeneous -glycoproteins with α-2,6-linkages in the periplasm of and will facilitate the construction of strains capable of producing terminally sialylated -glycoproteins in high yield.