New lectins from Codium isthmocladum Vickers show unique amino acid sequence and antibiofilm effect on pathogenic bacteria

Two new lectins from the green alga Codium isthmocladum (CiL-1 and CiL-2) were isolated. Both lectins could agglutinate human and rabbit erythrocytes. Galactosides and fetuin showed inhibitory effect on CiL-1. CiL-2 was inhibited by GalNAc and porcine stomach mucin. CiL-1 was a monomeric protein of 12 kDa, whereas CiL-2 showed 12 kDa in SDS-PAGE and an oligomeric state in gel filtration. MALDI-ToF-MS of CiL-1 revealed a molecular mass of 12.027 ± 5 Da, while CiL-2 showed molecular mass of 12.264 ± 5 Da. Ninety-eight percent of CiL-1’s primary structure was determined consisting of 112 residues placed in two repeated domains with approximately 60% of similarity. CiL-1 showed similarity with hypothetical proteins from aquatic pathogenic fungi. The N-terminal of CiL-2 showed no similarity to CiL-1 or to any known protein. The three-dimensional model of CiL-1 consists of four two-strand β-sheets disposed in a barrel-like arrangement, connected by loops of variable sizes, with a well-structured hydrophobic core. Binding site prediction suggests the existence of two independent monosaccharide binding sites in CiL-1. The lectins showed no antibacterial activity on Gram-positive and Gram-negative bacteria, but they were able to significantly inhibit the biofilm formation from Staphylococcus aureus and Staphylococcus epidermidis.