Recognition of cell surface acceptors by two human α-2,6-sialyltransferases produced in CHO cells

Structure-Function Analysis of the Human Sialyltransferase ST3Gal I

“…In contrast, the replacement of the conserved Glu residue by glutamine did not inactivate the enzyme (25% residual activity compared with the wild type). However the strict conservation of HX 4 E motif in all the vertebrate STs characterized to date, as well as its predicted occurrence as a N-capping substructure of an ␣-helix (data not shown), strongly suggest that both residues are necessary for optimal catalytic efficiency of the glycosyl transfer reaction. From these observations and kinetic data, it is thus conceivable that motif 4 (VS) is part of the active site, mainly located on the acceptor side or at the vicinity of both donor and acceptor sugar substrates.…”

“…A, schematic representation of the topology of human ST3Gal I. The positions of potential N-glycosylation sites are shown by arrowheads and those that were mutated in the present study were numbered (1)(2)(3)(4). Black arrowheads indicate the N-glycan attachment sites conserved in all ST3Gal I sequences.…”

“…Whether the occurrence of disulfide bridge is a common feature to all STs remains to be established, but this would bring in close proximity sialylmotifs L and S and possibly residues at the N terminus of the catalytic domain near the catalytic center. The minimal catalytic domain has been defined experimentally for a few STs, or alternatively by sequence comparison (4,22,31). The proposed boundaries to delineate the stem region from the catalytic domain generally coincide, for each subfamily, with the end of a hypervariable region in the N-terminal ends of the polypeptides (Ref.…”

“…In this group, it appears that the broader the acceptor specificity, the longer the stem region (1). The stem region often displays high variability in amino acid composition and little secondary organization and was therefore predicted to be flexible (4). However, this peptide portion often contains cysteine residues as well as several N-and O-glycosylation sites, which could contribute to a local conformation.…”

The evolution of galactose α2,3-sialyltransferase: Cionaintestinalis ST3GAL I/II and Takifugu rubripes ST3GAL II sialylate Galβ1,3GalNAc structures on glycoproteins but not glycolipids

“…This is followed by a stem region and a large C-terminal catalytic domain that faces the Golgi lumen. A comparison of peptide sequences strongly indicates that the length and amino acid composition of catalytic domains are relatively well conserved between STs and variations in protein sizes are generally attributable to differences in the length of the stem region [10]. All eukaryotic STs exhibit conserved peptide regions in their catalytic domain referred to as L (long)-, S (short)-and VS (very short) sialylmotifs, suggesting their common ancestry [11,12].…”