A novel galectin with triple carbohydrate recognition domain in the parotoid secretion of Rhinella diptycha.

Galectins are a family of animal lectins involved in cell adhesion, tumor differentiation, and apoptosis that can bind reversibly to carbohydrates with a high affinity for β-galactosides. Thus far, however, the primary structure and solved three-dimensional structure have been described for only a few amphibian galectins. Therefore, this work aimed to identify and structurally characterize the galectin (RdG) present in the secretion of the parotid gland of R. diptycha. RdG was partially purified and identified through hemagglutinating activity. The partial primary structure was obtained using peptide sequencing obtained from proteolysis with different enzymes, resulting in a sequence comprising 393 amino acids (86,4 % of coverage). In addition, based on alignments with homologous proteins, the complete sequence was predicted to consist of 455 residues with a molecular mass of 51 kDa and a triple carbohydrate recognition domain (CRD). The three-dimensional structure was then predicted, and protein-carbohydrate interaction was analyzed by molecular docking. The signature sequence of a highly conserved domain was identified in RdG with residues differing somewhat from those of other galectins. Thus, with the structural data for RdG, we were well positioned to better understand the interactions between ligands and amino acid residues of this novel triple CRD galectin. Given the therapeutic potential of galectins in general, structural studies like this one are crucial for understanding the mechanisms of action of galectins like RdG.