Structural Characterization of a Proto-Type Galectin from Cinachyrella sp. and Evaluation of Its Selective Bacterial Glycan Recognition and Antibiofilm Activity

Marine sponges represent a rich source of lectins with diverse biological activities and biotechnological potential. In this study, we report the purification and comprehensive biochemical and structural characterization of a lectin (CspL) from the marine sponge Cinachyrella sp. and evaluate its effects on bacterial agglutination, planktonic bacterial growth, and biofilm formation. CspL was isolated using classical chromatographic approaches and identified as a galectin-like protein based on sequence similarity, conserved carbohydrate-recognition motifs, and a predominance of β-sheet structures revealed by circular dichroism. Oligomeric analysis indicated a homotetrameric organization, consistent with the quaternary structure described for other sponge proto-type galectins. Carbohydrate-binding assays demonstrated that CspL preferentially recognizes galactoside-containing motifs, showing strong inhibition by mucin-type glycoproteins, while displaying lower affinity toward more complex glycan structures. This binding profile suggests a preference for accessible carbohydrate epitopes, likely associated with its canonical galectin architecture. Regarding antibacterial activity, CspL also exhibited selective, carbohydrate-dependent bacterial agglutination, particularly against Staphylococcus aureus strains. In addition, CspL exhibited antibiofilm activity against S. aureus and Escherichia coli, significantly reducing biofilm biomass and viable cell counts. Additionally, the lectin modulated antibiotic activity, showing synergistic effects with tetracycline and strain-dependent interactions with oxacillin. Together, these findings highlight CspL as a structurally conserved yet functionally relevant member of sponge galectins and reinforce the role of structural diversity in shaping glycan recognition and antimicrobial activity in marine lectins.