Evidence for Conformational Mechanism on the Binding of TgMIC4 with β-Galactose-Containing Carbohydrate Ligand

Abstract

A deeper understanding of the role of sialic/desialylated groups during TgMIC4-glycoproteins interactions has importance to better clarify the odd process of host cell invasion by members of the apicomplexan phylum. Within this context, we evaluated the interaction established by recombinant TgMIC4 (the whole molecule) with sialylated (bovine fetuin) and desialylated (asialofetuin) glycoproteins by using functionalized quartz crystal microbalance with dissipation monitoring (QCM-D). A suitable receptive surface containing recombinant TgMIC4 for monitoring β-galactose-containing carbohydrate ligand (limit of quantification ∼ 40 μM) was designed and used as biomolecular recognition platform to study the binding and conformational mechanisms of TgMIC4 during the interaction with glycoprotein containing (fetuin), or not, terminal sialic group (asialofetuin). It was inferred that the binding/interaction monitoring depends on the presence/absence of sialic groups in target protein and is possible to be differentiated through a slower binding kinetic step using QCM-D approach (which we are inferring to be thus associated with β-galactose ligand). This slower binding/interaction step is likely supposed (from mechanical energetic analysis obtained in QCM-D measurements) to be involved with Toxoplasma gondii (the causative agent of toxoplasmosis) parasitic invasion accompanied by ligand (galactose) induced binding conformational change (i.e., cell internalization process can be additionally dependent on structural conformational changes, controlled by the absence of sialic groups and to the specific binding with galactose), in addition to TgMIC4-glycoprotein solely recognition binding process.

The lectin-specific activity of Toxoplasma gondii microneme proteins 1 and 4 binds Toll-like receptor 2 and 4 N-glycans to regulate innate immune priming

“…Based on the sugar recognition selectivity of rMIC1 and rMIC4, we tested two oligosaccharides (α(2–3)-sialyllactose and lacto-N-biose) for their ability to inhibit the interaction of the MICs with the glycoproteins fetuin and asialofetuin [26]. Sialyllactose inhibited the binding of rMIC1 to fetuin, and lacto-N-biose inhibited the binding of rMIC4 to asialofetuin (Fig 1B).…”

The Potential Contribution of ABO, Lewis and Secretor Histo-Blood Group Carbohydrates in Infection by Toxoplasma gondii

“…T. gondii induces conformational changes in the microneme complex TgMIC4. This complex can bind various galactose-containing carbohydrates (Marchant et al, 2012;Santos et al, 2015). Chinese hamster ovary cells deficient in sialic acid, a widely distributed monosaccharide on the cell surface of all vertebrates, are resistant to infection by T. gondii (Monteiro et al, 1998).…”

Glycoprotein assay based on the optimized immittance signal of a redox tagged and lectin-based receptive interface

“…The adsorption of proteins to functionalized surfaces has received great attention (Fang et al, 2005;Chen et al, 2010;Rabe et al, 2011;Wiseman and Frank, 2012;Santos et al, 2015a) due to the possibility of quantifying bio-interaction (or bio-recognition) thus providing new insights in comprehending the role of certain proteins in biological systems (Nelson and Cox, 2012), specifically in cell-cell interactions (Ramburth and Dwek, 2011;Marchant et al, 2012;Carvalho et al, 2014). For example, lectins, a class of carbohydrate binding proteins, have been used as biorecognition elements for cancer cell detection (Ramburth and Dwek, 2011;Hu et al, 2013) which suffer some structural changes clearly as a consequence of disease onset (Reis et al, 2010;Clark and Mao, 2012).…”

“…The advantage of these techniques is the capability to investigate interaction kinetics in real-time (Lebed et al, 2006;Pedroso et al, 2008;Pesquero et al, 2010). This technique can also incorporate analysis of the energy dissipation factor (QCM-D), additionally allowing investigation of the viscoelastic properties of proteinprotein binding/interactions (Höök and Kasemo, 2007), eventually associated with different binding processes or recognition events (Giménez-Romero et al, 2013;Santos et al, 2015a). Similar to QCM, Surface Plasmon Resonance (SPR) is a technique in which the transducing signal is intrinsically and related to changes in the optical properties of the investigated receptive surface.…”