Sialyltransferase 0160, a bacterial sialyltransferase which catalyzes the incorporation of NeuAc from CMP-NeuAc into the galactose residue of the carbohydrate chain at position 6, is produced by Photobacterium damsela JT0160. The gene coding for sialyltransferase 0160 (bst) was cloned, sequenced, and expressed in Escherichia coli. The sialyltransferase 0160 gene contains an open reading frame of 2,028 base pairs encoding a protein of 675 amino acid residues. The deduced amino acid sequence of sialyltransferase 0160 did not contain the sialylmotif and had no significant similarity to mammalian sialyltransferases. Crude extracts of cultured E. coli MV1184 cells carrying an expression plasmid for the sialyltransferase 0160 gene showed sialyltransferase activity, which was identified as beta-galactoside alpha2,6-sialyltransferase activity by enzymatic reaction product analysis. In addition, when mutant genes, lacking 3'-coding regions for COOH-terminal portions of the protein, which are thought to form alpha-helix structures, were expressed in E. coli MV1184, soluble-form enzymes were obtained. This implies that the COOH-terminal portion of sialyltransferase 0160 is required for membrane binding.

The substrate specificity and enzymatic sialylation ability of the bacterium α-2,6-sialyltransferase were examined. The enzyme assay displayed a remarkable ability to catalyze sialyl transfer to type-II oligosaccharides possessing fucoside or sialoside at the 2 or 3 position of the terminal galactoside. Enzymatic syntheses were performed in order to confirm the structure of unusual assay products found when using Neu5Ac β2,3Galβ1,4Glc and Fuc α1,2Galβ1,4Glc as the sialyl acceptors. Both sialylation reactions (10 μmol scales) were run using 83 munits of enzyme, were complete in 2 h, and afforded the sialoside analogues Neu5Ac α2,6(Fuc α1,2) Galβ1,4Glc (88%) and Neu5Ac α2,6(Neu5Ac β2,3) Galβ1,4Glc (92%).

A bacterial sialyltransferase, named sialyltransferase 0160, was purified from a marine bacterium that had been isolated from seawater from Sagami Bay, Kanagawa. This strain has been identified as Photobacterium damsela, and named P. damsela JT0160. Sialyltransferase 0160 was purified 688-fold to homogeneity from the crude extract of the cells with a yield of 19% using a combination of anion exchange chromatography, hydroxyapatite chromatography, gel filtration chromatography, and affinity chromatography. The purified enzyme migrated as a single band (61 kDa) on sodium dodecyl sulfate-polyacrylamide gel. This sialyltransferase was found to be a beta-galactoside alpha 2,6-sialyltransferase [EC 2.4.99.1] which catalyzes the incorporation of NeuAc from CMP-NeuAc into the galactose residue of the carbohydrate chain at position 6 on the basis of an analysis of the enzymatic reaction products with HPLC, 1H-, 13C-NMR spectroscopy, and fast atom bombardment mass spectroscopy.