Sponge Galectins: Structure, Evolution, and Function.

Marine organisms display remarkable chemical diversity and are a prolific source of bioactive molecules. Among these compounds are lectins, proteins or glycoproteins that have specific and reversible binding to carbohydrates. However, lectins do not alter the properties of their ligands and are not derived from adaptive immune responses. In animals, lectins are structured into families. Galectins constitute a well-defined family characterized by their affinity for β-galactosides and the presence of a conserved carbohydrate recognition domain (CRD). These proteins are widespread across the animal kingdom, from sponges to vertebrates, and are involved in diverse physiological processes, including cell recognition, signaling, and immune modulation. Sponges (phylum Porifera), as the earliest metazoans, have emerged as valuable models for understanding the structural evolution and functional diversification of lectins. Although several sponge lectins have been isolated, only a limited number have been fully characterized at the molecular level. Within this group, galectins are particularly intriguing due to their structural variability and distinctive carbohydrate-binding properties compared to their vertebrate counterparts. To date, eight sponge species have been reported to produce galectins, yet only three-dimensional (3D) structures have been experimentally determined. This scarcity of structural data limits our understanding of the evolutionary and functional aspects of these molecules. In this review, we summarize current advances in the structural and biochemical characterization of sponge galectins, compare their primary and predicted tertiary structures with those of vertebrate galectins, and discuss their emerging biotechnological potential.