Structural characterization of a galectin from the marine sponge Aplysina lactuca (ALL) with synergistic effects when associated with antibiotics against bacteria.

Lectins presents the ability to interact with glycans and trigger varied responses, including the inhibition of the development of various pathogens. Structural studies of these proteins are essential to better understand their functions. In marine sponges, so far only a few lectins have their primary structures completely determined. Thus, the objective of this work was to structurally characterize and evaluate antibacterial potential, in association with different antibiotics, of the lectin isolated from the marine sponge Aplysina lactuta (ALL). ALL is a homotetramer of 60 kDa formed by four 15 kDa-subunits. The lectin showed affinity only for the glycoproteins fetuin, asialofetuin, mucin type III, and bovine submaxillary mucin type I. The complete amino acid sequences of two isoforms of ALL, named ALL-a and ALL-b, were determined by a combination of Edman degradation and overlapped peptides sequenced by tandem mass spectrometry. ALL-a and ALL-b have 144 amino acids with molecular masses of 15,736 Da and 15,985 Da, respectively. Both structures contain conserved residues typical of the galectin family. ALL is a protein with antibacterial potential, when in association with ampicillin and oxacillin the lectin potentiates its antibiotic effect, included Methicillin-resistant Staphylococcus strains. Thus, ALL shows to be a molecule with potential for the development of new antibacterial drugs.

A new mucin-binding lectin from the marine sponge Aplysina fulva (AFL) exhibits antibiofilm effects.

A new mucin-binding lectin (AFL) was isolated from the marine sponge Aplysina fulva. AFL was purified by affinity chromatography on Sepharose™ matrix. Its hemagglutinating activity was independent of divalent ions, and it was weakly inhibited by simple sugars. However, porcine stomach mucin was a powerful inhibitor. In SDS PAGE, piridylethylated AFL showed one band of approximately 16 kDa, whereas in the non-reducing conditions, AFL showed at least two bands of 30 and 70 kDa. Mass spectrometry MALDI-ToF analysis showed one major ion of 31,652 ±â€¯5 Da, which corresponded to a dimer formed by subunits linked by disulfide bonds. The first fifteen amino acids of AFL were determined, and no sequence similarity was observed with any known protein. Internal sequences were obtained by mass spectrometry analysis of tryptic digestion of AFL spots. These peptides showed similarity with a lectin from marine sponge Aplysina lactuca. Secondary structure of AFL was predominantly formed by ß-conformations, which were stable at variations of pH and temperature. AFL did not inhibit planktonic growth of Gram-positive and Gram-negative bacteria tested. However, the lectin did significantly reduce the biomass biofilm of the bacteria Staphylococcus aureus, S. epidermidis, and Escherichia coli.

Purification, Biochemical Characterization, and Amino Acid Sequence of a Novel Type of Lectin from Aplysia dactylomela Eggs with Antibacterial/Antibiofilm Potential.

A new lectin from Aplysia dactylomela eggs (ADEL) was isolated by affinity chromatography on HCl-activated Sepharose™ media. Hemagglutination caused by ADEL was inhibited by several galactosides, mainly galacturonic acid (Ka = 6.05 × 106 M-1). The primary structure of ADEL consists of 217 residues, including 11 half-cystines involved in five intrachain and one interchain disulfide bond, resulting in a molecular mass of 57,228 ± 2 Da, as determined by matrix-assisted laser desorption/ionization time of flight mass spectrometry. ADEL showed high similarity with lectins isolated from Aplysia eggs, but not with other known lectins, indicating that these lectins could be grouped into a new family of animal lectins. Three glycosylation sites were found in its polypeptide backbone. Data from peptide-N-glycosidase F digestion and MS suggest that all oligosaccharides attached to ADEL are high in mannose. The secondary structure of ADEL is predominantly ß-sheet, and its tertiary structure is sensitive to the presence of ligands, as observed by CD. A 3D structure model of ADEL was created and shows two domains connected by a short loop. Domain A is composed of a flat three-stranded and a curved five-stranded ß-sheet, while domain B presents a flat three-stranded and a curved four-stranded ß-sheet. Molecular docking revealed favorable binding energies for interactions between lectin and galacturonic acid, lactose, galactosamine, and galactose. Moreover, ADEL was able to agglutinate and inhibit biofilm formation of Staphylococcus aureus, suggesting that this lectin may be a potential alternative to conventional use of antimicrobial agents in the treatment of infections caused by Staphylococcal biofilms.