Galectin-like protein 2: A new non-mammalian member of the galectin family

The galectin family comprises evolutionarily conserved soluble animal lectins. Recently, a new member of this family was described: galectin-like 2 (LGALSL2). This protein consists of a globular domain that shares the structural organization of galectin carbohydrate recognition domains, but lacks some of the amino acids necessary for binding to β-galactosides. Although LGALSL2 is widespread in jawed vertebrates, this protein is absent in mammals. The amino acid sequence is highly conserved from cartilaginous fish to birds. The focus of this conservation is on the convex face of the protein, which is located opposite the putative glycan-binding groove. In chickens, LGALSL2 is predominantly expressed in the testis and epididymis. We demonstrated that recombinant chicken LGALSL2 protein binds to vesicle structures in the Sertoli cell cytoplasm as well as in epididymal ductuli efferentes proximales vesicles. The location of these vesicles indicates their potential role in the formation and resorption of the seminiferous fluid. These vesicle structures are both rich in carbohydrates. However, broad-spectrum glycan microarray screening revealed that, under the tested conditions, LGALSL2 did not show significant binding to the glycan sequences, with only very weak signals observed for to a few fucosylated glycans. The results suggest that LGALSL2 does not have a classic galectin function. Instead, it may recognise 'exotic' glycans not represented in the screening array, or its activity may depend less on glycan-protein interactions and more on protein-protein interactions. As these binding partners of LGALSL2 appear to be involved in the formation and turnover of seminiferous tubular fluid, it is suggested that this new galectin-like protein may be involved in the maturation of sperm in chickens.