The trans-sialidase from Trypanosoma cruzi efficiently transfers α-(2→3)-linked N-glycolylneuraminic acid to terminal β-galactosyl units

The trans-sialidase from Trypanosoma cruzi (TcTS), the agent of Chagas’ disease, is a unique enzyme involved in mammalian host-cell invasion. Since T. cruzi is unable to synthesize sialic acids de novo, TcTS catalyzes the transfer of α-(2→3)-sialyl residues from the glycoconjugates of the host to terminal β-galactopyranosyl units present on the surface of the parasite. TcTS also plays a key role in the immunomodulation of the infected host. Chronic Chagas’ disease patients elicit TcTS-neutralizing antibodies that are able to inhibit the enzyme. N-Glycolylneuraminic acid has been detected in T. cruzi, and the trans-sialidase was pointed out as the enzyme involved in its incorporation from host glycoconjugates. However, N-glycolylneuraminic acid α-(2→3)-linked-containing oligosaccharides have not been analyzed as donors in the T. cruzi trans-sialidase reaction. In this paper we studied the ability of TcTS to transfer N-glycolylneuraminic acid from Neu5Gc(α2→3)Gal(β1→4)GlcβOCH2CH2N3 (1) and Neu5Gc(α2→3)Gal(β1→3)GlcNAcβOCH2CH2N3 (2) to lactitol, N-acetyllactosamine and lactose as acceptor substrates. Transfer from 1 was more efficient (50–65%) than from 2 (20–30%) for the three acceptors. The reactions were inhibited when the enzyme was preincubated with a neutralizing antibody. Km values were calculated for 1 and 2 and compared with 3′-sialyllactose using lactitol as acceptor substrate. Analysis was performed by high-performance anion-exchange (HPAEC) chromatography. A competitive transfer reaction of compound 1 in the presence of 3′-sialyllactose and N-acetyllactosamine showed a better transfer of Neu5Gc than of Neu5Ac.

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