![]() ![]() Instead the parasite scavenges it from host's sialyl glycoconjugates using its frans-sialidase activity (TcTS Previato et al., 1985). One of the most elegant mechanisms of cell-surface sialylation is exploited by the protozoal parasite Trypanosoma cruzi, the etiological agent of Chagas' disease (Coura and Viñas, 2010). The evolutionary advantage of this molecular mimicry is so evident that several parasites exploit cell-surface sialylation to survive within the host environment and establish the infection (Vimr and Lichtensteiger, 2002). Through molecular mimicry while unsialylated strains are rapidly cleared. Further, Sia play a major role protecting the infective agent from the host's immune response Sia are also important as recognition sites in host-pathogen interactions acting as ligands for parasite adherence, possibly driving natural selection (Varki, 2006). They are targets of Sia-binding lectins and can mask underlying structures, for example impeding the binding of Gal-specific receptors (Sorensen et al., 2009 Rabinovich et al., 2012). Because of the negative charge, these molecules affect the recognition and anti-recognition phenomena. Sia-containing glycoconjugates are involved in a myriad of cell functions. In vertebrates, Sia are commonly linked via an a2-3 linkage to galactopyranose (Galp), via an a2-6 linkage to Galp and N-acetylgalactosamine (GalNAc), or via an a2-8 linkage to another Sia (Varki et al., 2009). The final product of this complex biosynthetic pathway, the activated form of Sia (CMP-Sia), is transferred to the non-reducing end of newly synthesized glycan chains by a family of sialyltransferases present in the Golgi lumen. ![]() The metabolism of Sia in mammals involves 32 genes that encode enzymes and transporters, distributed among the different compartments of the cell (Wickramasinghe and Medrano, 2011). The most common members of this family are the N-acetylneuraminic acid and its derivative the N-glycolylneuraminic acid that differ from each other at position 5 (C-5), which is substituted with an acetamido or a hydroxyacetamido moiety respectively (Figure 1). Sialic acids (Sia) are 9-carbon backbone acidic monosaccharides found at prominent positions of the sugar chains of glycoconju-gates present on cell membranes or secreted into the extracellular medium. Keywords: glycoconjugate, sialic acid, sialidase, parasite, immune response This review presents the state of the art of parasite sialobiology, highlighting how the interplay between host and parasite sialic acid helps the pathogen to evade host defense mechanisms and ensure lifetime host parasitism. Additionally, TcTS activity is capable of extensively remodeling host cell glycomolecules, playing a role as virulence factor. Studies of the parasite cell surface architecture and biochemistry indicate that a unique system comprising sialoglycoproteins and sialyl-binding proteins assists the parasite in several functions including parasite survival, infectivity, and host-cell recognition. Mammals synthesize sialic acid through a complex pathway, but Trypanosoma cruzi, the agent of Chagas' disease, evolved to obtain sialic acid from its host through a frans-sialidase (TcTS) reaction. Wanderley De Souza, Universidade Federal do Rio de Janeiro, Brazil Reviewed by:Į-mail: found at the outermost ends of complex carbohydrates in extracellular medium or on outer cell membranes, sialic acids play important roles in a myriad of biological processes. Laboratorio de Glicobiologia Estrutural e Funcional, Instituto de Biofísica Carlos Chagas Fiiho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil Penha, Frederico Alisson-Silva, Wagner B. Sialic acid: a sweet swing between mammalian host and Trypanosoma cruzi
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