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

摘要

On the basis of the results outlined in our previous report, bacterial sialyltransferases (ST) from marine sources were further characterized using glycosphingolipids (GSL), especially ganglio-series GSLs, based on the enzymatic characteristics and kinetic parameters obtained by Line weaver-Burk plots. Among them, GA1 and GA2 were found to be good substrates for these unique STs. Thus, new gangliosides synthesized by 2-3 and 2-6STs were structurally characterized by several analytical procedures. The ganglioside generated by the catalytic activity of 2-3ST was identified as GM1b. On the other hand, when enzyme reactions by 2-6STs were performed using substrates GA2 and GA1, very unique gangliosides were generated. The structures were identified as NeuAc2-6GalNAc{beta}1-4Gal{beta}1-4Glc{beta}-Cer and NeuAc2-6Gal{beta}1-3GalNAc{beta}1-4Gal{beta}1-4Glc{beta}-Cer, respectively. The synthesized ganglioside NeuAc2-6GalNAc{beta}1-4Gal{beta}1-4Glc{beta}-Cer showed binding activity to the influenza A virus {A/Panama/2007/99 (H3N2)} at a similar level to purified sialyl(2-3)paragloboside (S2-3PG) and sialyl(2-6)paragloboside (S2-6PG) from mammalian sources. The evidence suggests that these STs have unique features, including substrate specificities restricted not only to lacto-series but also to ganglio-series GSLs, as well as catalytic potentials for ganglioside synthesis. This evidence demonstrates that effective in vitro ganglioside synthesis could be a valuable tool for selectively synthesizing sialic acid (Sia) modifications, thereby preparing large-scale gangliosides and permitting the exploration of unknown functions.