Download MendeleyThe structure of human alpha-2,6-sialyltransferase reveals the binding mode of complex glycans.
Kuhn, B., Benz, J., Greif, M., Engel, A.M., Sobek, H., Rudolph, M.G.(2013) Acta Crystallogr D Biol Crystallogr 69: 1826-1838
- PubMed: 23999306
- DOI: https://doi.org/10.1107/S0907444913015412
- Primary Citation of Related Structures:
4JS1, 4JS2 - PubMed Abstract:
Human β-galactoside α-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.
Organizational Affiliation:
pRED Pharma Research and Early Development, Discovery Technologies, F. Hoffmann-La Roche AG, Grenzacher Strasse 124, 4070 Basel, Switzerland.
