Bioactive gangliosides: analysis of functional structures of the tetrasialoganglioside G Q1b which promotes neurite outgrowth

Abstract

Previous reports from our laboratory showed that tetrasialoganglioside G Q1b, when exogenously added, can promote cell proliferation and neurite outgrowth in two human neuroblastoma cell lines, GOTO and NB-1 (Tsuji, S., Arita, M. and Nagai, Y. (1983) J. Biochem. 94, 303–306). To clarify the activity-associated structure of G Q1b, we analyzed the structure-activity relationships using the G Q1b, molecule, derivatives of it, and related gangliosides. When the G Q1b molecule was divided into two parts, the ceramide and oligosaccharide moieties, no activity was found with the former, while with the latter the activity could be seen, although the level of activity obtained never exceeded half that of G Q1b itself and an optimal concentration of 100–200 ng/ml of 20–40-times that of native G Q1b (5 ng/ml) was required. Furthermore, the activity of G Q1b was completely abolished by neuraminidase treatment, which converted G Q1b to G M1, so we examined other molecular species of gangliosides having a common gangliotetraose backbone but linked differently with two to four sialic acids (i.e., G D1a, G D1b, G T1a G Q1c G Q1b and G Q1c). Among them, only G Q1b was found to be active. The results disclosed the interesting fact that deletion of any sialic acid residue from either of the two disialosyi residues of G Q1b results in a complete loss of activity and that the mere existence of the tetrasialosyl structure does not lead to activity; this indicates the absolute necessity of the G Q1b oligosaccharide structure for the expression of activity. For full expression of the activity, both the ceramide and oligosaccharide moieties were necessary. It was also found that the G Q1b oligosaccharide inhibited the activity of G Q1b at a concentration a few times greater than that of G Q1b, suggesting the involvement of a receptor-like mechanism in the action of G Q1b at the cell membrane.