STRUCTURAL AND FUNCTIONAL ASPECTS OF GALECTIN-9 GENE IN Labeo rohita

Galectins are proteins having affinity for beta-galactoside, characterized by a conserved sequence motif in their CRDs which exclusively recognize and bind specific sugars on cell surface by carbohydrate recognition domain (CRD). Under non-infectious stressful conditions, the release of galectins to the extracellular space can be perceived as a "danger-associated molecular pattern", a signal that can trigger inflammatory responses. Galectins in extracellular space can also recognize potential pathogens and parasites. They function by binding the pathogens directly or modulating the immune system in response to the infection. We studied the structural aspects of Labeo rohita galectin-9 gene (LrGal-9) to gain insights into its functionality.

The animals (L. rohita) were procured from a fish farm located in Maharashtra. Total RNA was extracted from gill tissue and was converted to its complementary DNA. Galectin-9 gene was characterized and the bioinformatics analysis was performed. The analysis revealed LrGal-9 possesses two distinct CRDs joined by a linker of 50 amino acids. Each CRD has eight conserved sugar binding sites (H-N-R, V-N, and W-E-R) required for binding terminal sugars on the pathogens (Fig.1). Thirteen potential tyrosine phosphorylation sites and three N-linked glycosylation sites were predicted using NetPhos 3.1 and NetNGlyc 1.0 respectively. Prediction of transmembrane region and signal peptide in LrGal-9 was performed using TMHMM v. 2.0. and SignaIP program respectively. Neither signal peptide nor the transmembrane region was present in LrGal-9. The deduced 291 amino acid sequence of LrGal-9 was used to predict the protein-protein interaction with other biological molecules using STRING software. LrGal-9 forms network with PDZ binding kinase, Lymphokine-activated killer T-cell-originated protein kinase, Inhibitor of nuclear factor kappa-B kinase subunit epsilon, and many other biological molecules (Fig.2). Presence of all the conserved residues (H-N-R, V-N, and W-E-R) indicated that the carbohydrate-binding specificity of LrGal-9 empowers it to act as a pathogen recognition receptor and networking analysis revealed the it regulates important downstream functions in biological systems.