Specificity of human trans-sialidase as probed with gangliosides

It has been shown that human blood contains a soluble 67 kDa enzyme, belonging by its donor–acceptor properties to trans-sialidases. The enzyme is capable of both cleaving and synthesizing α2-3 and α2-6 sialosides [Atherosclerosis2001, 159, 103]. In this work the study of donor–acceptor specificity of the new enzyme was extended. It has been demonstrated in vitro that trans-sialidase possesses the ability of transferring Neu5Ac residue to acceptor (asialofetuin) both from α2-3- (GM1, GM3, GD1a), and α2-8-sialylated gangliosides (GD3 and GD1b, but not GT1b and GQ1b). Transfer of radiolabeled Neu5Ac from fetuin to glycosphingolipids demonstrated that Lac-Cer > mono- and disialogangliosides > GT1b > GQ1b were acceptors for this enzyme. Two methods were used to reveal whether α2-8 bond can be formed between Neu5Ac residues during trans-sialylation, that is immunochemical detection using monoclonal antibodies specific to α2-8 di- and oligosialic acids, and fluorometric C7/C9 analysis. Both methods demonstrated the formation of Neu5Acα2-8Neu5Ac termination by trans-sialidase, for example, in case of the use 3′SL as sialic acid donor and Neu5Ac-PAA or LDL as acceptor. Thus, human trans-sialidase in vitro displays wide substrate specificity: the enzyme is capable of digesting as well as synthesizing α2-3, α2-6, and α2-8 sialosides.