Synthesis of a model trisaccharide for studying the interplay between the anti £\-Galp antibody and the trans-sialidase reactions in Trypanosoma cruzi

GIORGI, ME; LOPEZ, R.; AGUSTI, R; MUCHNIK DE LEDERKREMER, R

CARBOHYDRATE RESEARCH

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2017 vol. 450 p. 30 - 37

0008-6215

Trypanosoma cruzi, the etiologic agent of Chagas disease, is covered by a dense glycocalix mainly composed by glycoproteins called mucins which are also the acceptors of sialic acid in a reaction catalyzed by a trans-sialidase (TcTS). Sialylation of trypomastigote mucins protects the parasite from lysis by the anti £-Galp antibodies from serum. The TcTS is essential for the infection process since T. cruzi is unable to biosynthesize sialic acid. The enzyme specifically transfers it from a terminal £]-D-Galp unit in the host glycoconjugate to terminal £]-D-Galp units in the parasite mucins to construct the D-NeuNAc(£¡÷3)£]-D-Galp motif. On the other hand, although galactose is the most abundant sugar in mucins of both, the infective trypomastigotes and the insect stage epimastigotes, £-D-Galp is only present in the infective stage whereas £]-D-Galf is characteristic of the epimastigote stage of the less virulent strains. Neither D-Galp nor D-Galf is acceptor of sialic acid. In the mucins, some of the oligosaccharides are branched with terminal £]-D-Galp units to be able to accept sialic acid in the TcTS reaction.While the D-Galf containing oligosaccharides from epimastigotes have been fully characterized and chemically synthesized, information on the fine structure of the carbohydrates in the trypomastigote mucins is still scarce. Based on previous reports showing that anti £-Galp antibodies only partially colocalize with sialic acid, we have undertaken the synthesis of the trisaccharide £-D-Galp(1¡÷3)-[£]-D-Galp(1¡÷6)]-D-Galp, the smallest structure containing both, the antigenic D-Galp(£¡÷3)-D-Galp unit and the sialic acid-acceptor £]-D-Galp unit. The trisaccharide was obtained as the 6-aminohexyl glycoside to facilitate further conjugation for biochemical studies and it was successfully sialylated by TcTS using either 3¡¦-sialyllactose or fetuin as donors. The product, ?¦-aminohexyl?n?Ñ-D-NeuNAc(2¡÷3)-£]-D-Galp(1¡÷6)-[£-D-Galp(1¡÷3)]-?Ò-D-Galp, was purified and characterized.