Unique gangliosides synthesized in vitro by sialyltransferases from marine bacteria and their characterization: ganglioside synthesis by bacterial sialyltransferases

On the basis of the results outlined in our previous report, bacterialsialyltransferases (ST) from marine sources were further characterized usingglycosphingolipids (GSL), especially ganglio-series GSLs, based on the enzymaticcharacteristics and kinetic parameters obtained by Line weaver-Burk plots. Amongthem, GA1 and GA2 were found to be good substrates for these unique STs. Thus,new gangliosides synthesized by α2-3 and α2-6STs were structurallycharacterized by several analytical procedures. The ganglioside generated by thecatalytic activity of α2-3ST was identified as GM1b. On the other hand,when enzyme reactions by α2-6STs were performed using substrates GA2 andGA1, very unique gangliosides were generated. The structures were identified asNeuAcα2-6GalNAcβ1-4Galβ1-4Glcβ-Cer andNeuAcα2-6Galβ1-3GalNAcβ1-4Galβ1-4Glcβ-Cer,respectively. The synthesized gangliosideNeuAcα2-6GalNAcβ1-4Galβ1-4Glcβ-Cer showed binding activityto the influenza A virus {A/Panama/2007/99 (H3N2)} at a similar level topurified sialyl(α2-3)paragloboside (S2-3PG) andsialyl(α2-6)paragloboside (S2-6PG) from mammalian sources. The evidencesuggests that these STs have unique features, including substrate specificitiesrestricted not only to lacto-series but also to ganglio-series GSLs, as well ascatalytic potentials for ganglioside synthesis. This evidence demonstrates thateffective in vitro ganglioside synthesis could be a valuable tool forselectively synthesizing sialic acid (Sia) modifications, thereby preparinglarge-scale gangliosides and permitting the exploration of unknownfunctions.