The action of Trypanosoma cruzi trans‐sialidase on glycolipids and glycoproteins

Abstract

Addition of sialic acid residues in the human pathogen Trypanosoma cruzi glycoconjugates is mediated by a trans-sialidase and not by a CMP-sialic acid : glycoconjugate sialyltransferase. Incubation of trans-sialidase with N-[galact~se-'~C]acetyllactosamine and 0-linked oligosaccharides, Nlinked glycopeptides (both obtained from fetuin) or sialyllactose showed that the last three compounds were donors of sialic acid residues to the first one. Moreover, N-and 0-linked oligosaccharides in asialofetuin and asialomucin, respectively, served as acceptors of sialic acid units. Gangliosides GM3, GD,, and GT,, but not GM2, GM,, nor GD,, donated sialic acid units to N-acetyllactos amine when incubated with trans-sialidase. This showed that only sialic acid units bound to terminal galactosyl residues were transferred. GMl, was converted to GD,,, and GD,, to GT,, when incubated with the appropriate donor. The fact that asialo-GM,, was converted to a ganglioside migrating as GD,, on thin-layer chromatography suggested that sialic acid units may be transferred to internal galactosyl residues, although once linked to those residues they can not be further transferred to other glycoconjugates. Sialic acid residues linked a2,3-but not a2,6-or a2,8-were transferred by the trans-sialidase. Methyl b-galactoside but not methyl a-galactoside served as acceptor of sialic acid units, thus suggesting that terminal a-linked galactosyl units in T cruzi and mammalian glycoproteins are not sialylated by the enzyme. As the trans-sialidase employed in these experiments has been shown to be located on the external surface of the parasite and to be shed to the medium, the relatively broad specificity shown by the enzyme with respect to protein-and lipid-linked oligosaccharides strongly suggests that infection by T cruzi might alter the sialic acid distribution in glycoproteins and glycolipids of the mammalian host.The human pathogen Trypanosoma cruzi differs from other eukaryotic and prokaryotic cells in the mechanism by which it adds sialic acid units to its glycoconjugates. Transfer of the above-mentioned residues appears to be mediated by a trans-sialidase activity and not by a CMP-sialic acid : glycoconjugate sialytransferase [l -31. It was reported that sialylation of a 2: cruzi structure by the trans-sialidase was required for the invasion of mammalian cells [3]. The activity has been detected in crude extracts of the parasite and found to recognize fetuin and short oligosaccharides as sugar donors and glycoproteins, short oligosaccharides and glycolipids as sialic acid acceptors but it was unknown if the enzyme recognized glycolipids as donor substrates or if it discriminated between N-, 0-and different lipid-linked oligosaccharides as acceptor and donor substrates. The activity assayed in crude preparations mainly required a2,3-linked sialic acid units as donors when the transfer to short oligosaccharides was tested but a2,6-linked sialic acid residues were about

The Lipid Structure of the Glycosylphosphatidylinositol-anchored Mucin-like Sialic Acid Acceptors of Trypanosoma cruzi Changes during Parasite Differentiation from Epimastigotes to Infective Metacyclic Trypomastigote Forms

“…Studies of TS specificity have shown that the enzyme is able to sialylate unbranched terminal ␤Galp residues, and that substitutions near the Gal decrease the extent of sialylation (39,40). We have confirmed these findings by using the purified O-linked oligosaccharides that are the natural acceptors on the parasite surface.…”

Glycobiology of Parasites: Role of Carbohydrate–Binding Proteins and Their Ligands in the Host–Parasite Interaction

“…In addition, affinity-purified enzyme inhibited attachment and invasion of sialylated cells, but not of the sialic acid deficient mutant (Ming et al, 1993). The specificity of a2,3-linkage of the sialic acid was shown by the finding that adhesion and invasion were blocked by a2,3-linked sialyllactose but not its a2,6-linked counterpart (Vandekerckhove et al, 1992;Ferrero-Garcia et al, 1993;Scudder et al, 1993). Transialidase is also believed to mediate attachment and invasion by sialylating parasite glycoproteins expressing the Ssp-3 epitope which has been shown to be involved in these processes (Schenkman et al, 1991.…”

Separation of Galfβ1→XGlcNAc and Galpβ1→XGlcNAc (X = 3, 4, and 6) as the Alditols by High-pH Anion-Exchange Chromatography and Thin-Layer Chromatography: Characterization of Mucins from Trypanosoma cruzi

“…These glycoproteins are involved in the mechanisms of invasion of the mammalian cell (5). The oligosaccharides responsible for this action function as acceptors of sialic acid in a trans-sialidase reaction (3,6). Single GlcNAc units are linked to threonine (3) or are further substituted with galactose.…”