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Publication Abstract from PubMed

Human beta-galactoside alpha-2,6-sialyltransferase I (ST6Gal-I) establishes the final glycosylation pattern of many glycoproteins by transferring a sialyl moiety to a terminal galactose. Complete sialylation of therapeutic immunoglobulins is essential for their anti-inflammatory activity and protein stability, but is difficult to achieve in vitro owing to the limited activity of ST6Gal-I towards some galactose acceptors. No structural information on ST6Gal-I that could help to improve the enzymatic properties of ST6Gal-I for biotechnological purposes is currently available. Here, the crystal structures of human ST6Gal-I in complex with the product cytidine 5'-monophosphate and in complex with cytidine and phosphate are described. These complexes allow the rationalization of the inhibitory activity of cytosine-based nucleotides. ST6Gal-I adopts a variant of the canonical glycosyltransferase A fold and differs from related sialyltransferases by several large insertions and deletions that determine its regiospecificity and substrate specificity. A large glycan from a symmetry mate localizes to the active site of ST6Gal-I in an orientation compatible with catalysis. The glycan binding mode can be generalized to any glycoprotein that is a substrate of ST6Gal-I. Comparison with a bacterial sialyltransferase in complex with a modified sialyl donor lends insight into the Michaelis complex. The results support an SN2 mechanism with inversion of configuration at the sialyl residue and suggest substrate-assisted catalysis with a charge-relay mechanism that bears a conceptual similarity to serine proteases.

The structure of human alpha-2,6-sialyltransferase reveals the binding mode of complex glycans.,Kuhn B, Benz J, Greif M, Engel AM, Sobek H, Rudolph MG Acta Crystallogr D Biol Crystallogr. 2013 Sep;69(Pt 9):1826-38. doi:, 10.1107/S0907444913015412. Epub 2013 Aug 17. PMID:23999306^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.