Synthesis and characterization of sialylated lactose- and lactulose-derived oligosaccharides by Trypanosoma cruzi trans-sialidase

Sialylated oligosaccharides contribute 12.6-21.9 % of total free oligosaccharides in human milk (hMOS). These acidic hMOS possess prebiotic properties and display anti-adhesive effects against pathogenic bacteria. Only limited amounts of sialylated hMOS are currently available. The aim of our work is to enzymatically synthesize sialylated oligosaccharides mimicking hMOS functionality. In this study we tested mixtures of glucosylated-lactose (GL34), galactosylated-lactulose (LGOS) and galacto-oligosaccharide (Vivinal GOS) molecules, as trans-sialylation acceptor substrates. The recombinant trans-sialidase enzyme from Trypanosoma cruzi (TcTS) was used for enzymatic decoration, transferring (α2→3)-linked sialic acid from donor substrates to the non-reducing terminal β-galactopyranosyl units of these acceptor substrates. The GL34 F2 2-glc-lac compound with an accessible terminal galactosyl residue was sialylated efficiently (conversion degree of 47.6 %). TcTS also sialylated at least five LGOS structures and eleven Vivinal GOS DP3-4 compounds. These newly synthesized sialylated oligosaccharides are interesting as potential hMOS-mimics for applications in biomedical and functional food products.