Abstract
Fourteen different active Trypanosoma congolense trans-sialidases (TconTS), 11 variants of TconTS1 besides TconTS2, TconTS3 and TconTS4, have been described. Notably, the specific transfer and sialidase activities of these TconTS differ by orders of magnitude. Surprisingly, phylogenetic analysis of the catalytic domains (CD) grouped each of the highly active TconTS together with the less active enzymes. In contrast, when aligning lectin-like domains (LD), the highly active TconTS grouped together, leading to the hypothesis that the LD of TconTS modulates its enzymatic activity. So far, little is known about the function and ligand specificity of these LDs. To explore their carbohydrate-binding potential, glycan array analysis was performed on the LD of TconTS1, TconTS2, TconTS3 and TconTS4. In addition, Saturation Transfer Difference (STD) NMR experiments were done on TconTS2-LD for a more detailed analysis of its lectin activity. Several mannose-containing oligosaccharides, such as mannobiose, mannotriose and higher mannosylated glycans, as well as Gal, GalNAc and LacNAc containing oligosaccharides were confirmed as binding partners of TconTS1-LD and TconTS2-LD. Interestingly, terminal mannose residues are not acceptor substrates for TconTS activity. This indicates a different, yet unknown biological function for TconTS-LD, including specific interactions with oligomannose-containing glycans on glycoproteins and GPI anchors found on the surface of the parasite, including the TconTS itself. Experimental evidence for such a scenario is presented.
Highlights
The protozoan parasite Trypanosoma congolense is the most prevalent cause of animal African Trypanosomiasis (AAT), called Nagana in cattle and other livestock, causing death to millions of animals resulting in huge economic losses [1,2,3]
In this study we demonstrated the binding of Trypanosoma congolense trans-sialidases (TconTS) lectin domains (TconTS-like” domain (LD)) to high-mannose N-glycans and provide evidence for a biological function for this interaction
To characterise the LDs of TconTS the gene sequences encoding the T. congolense possesses eleven TS1 (TconTS1)-LD, TconTS2-LD, TconTS3-LD and TconTS4-LD were subcloned into a modified pET28a bacterial expression vector as described under Methods
Summary
The protozoan parasite Trypanosoma congolense is the most prevalent cause of animal African Trypanosomiasis (AAT), called Nagana in cattle and other livestock, causing death to millions of animals resulting in huge economic losses [1,2,3]. The crystal structure of TcTS [14] revealed that the C-terminal domain folds into a β-barrel topology similar to that of known plant lectins such as GS4 (Griffonia simplicifolia lectin 4) [22], GNA (Galantus nivalis agglutinin, Snowdrop lectin) [23], LOL (Lathyrus ochrus lectin) [24] and WGA (Wheat germ agglutinin) [25]. This structural similarity suggests that the C-terminal domain may be a potential carbohydrate-binding site or “lectin-like” domain (LD).
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