Enzymatic basis for N-glycan sialylation: Structure of rat α2,6-sialyltransferase (ST6GAL1) reveals conserved and unique features for glycan sialylation

Lu Meng, Farhad Forouhar, David Thieker, Zhongwei Gao, Annapoorani Ramiah, Heather Moniz, Yong Xiang, Jayaraman Seetharaman, Sahand Milaninia, Min Su, Robert Bridger, Lucas Veillon, Parastoo Azadi, Gregory Kornhaber, Lance Wells, Gaetano T. Montelione, Robert J. Woods, Liang Tong, Kelley W. Moremen

Research output: Contribution to journalArticlepeer-review

75 Scopus citations

Abstract

Glycan structures on glycoproteins and glycolipids play critical roles in biological recognition, targeting, and modulation of functions in animal systems. Many classes of glycan structures are capped with terminal sialic acid residues, which contribute to biological functions by either forming or masking glycan recognition sites on the cell surface or secreted glycoconjugates. Sialylated glycans are synthesized in mammals by a single conserved family of sialyltransferases that have diverse linkage and acceptor specificities. We examined the enzymatic basis for glycan sialylation in animal systems by determining the crystal structures of rat ST6GAL1, an enzyme that creates terminal α2,6-sialic acid linkages on complex-type N-glycans, at 2.4 Å resolution. Crystals were obtained from enzyme preparations generated in mammalian cells. The resulting structure revealed an overall protein fold broadly resembling the previously determined structure of pig ST3GAL1, including a CMP-sialic acidbinding site assembled from conserved sialylmotif sequence elements. Significant differences in structure and disulfide bonding patterns were found outside the sialylmotif sequences, including differences in residues predicted to interact with the glycan acceptor. Computational substrate docking and molecular dynamics simulations were performed to predict and evaluate the CMP-sialic acid donor and glycan acceptor interactions, and the results were compared with kinetic analysis of active site mutants. Comparisons of the structure with pig ST3GAL1 and a bacterial sialyltransferase revealed a similar positioning of donor, acceptor, and catalytic residues that provide a common structural framework for catalysis by the mammalian and bacterial sialyltransferases.

Original languageEnglish (US)
Pages (from-to)34680-34698
Number of pages19
JournalJournal of Biological Chemistry
Volume288
Issue number48
DOIs
StatePublished - Nov 29 2013

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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