Caracterização estrutural e avaliação do potencial antimicrobiano em associação com antibióticos da lectina CiL-2 de Codium isthmocladum, novo membro das lectinas do Tipo-H

Abstract

Marine organisms, such as algae, represent a rich source of bioactive compounds, with lectins standing out as a notable group. Lectins are a category of proteins or glycoproteins capable of binding to carbohydrates, showing potential applications in health, including diagnostics. Structural studies of lectins are crucial, as their biological activities are linked to proteincarbohydrate interactions, decoding information within glycoconjugates and driving functions in living organisms. The objective of this study was to structurally characterize the lectin CiL2 present in the marine macroalga Codium isthmocladum and evaluate its antimicrobial potential in combination with antibiotics. CiL-2 primary structure was determined by overlapping peptides sequenced by mass spectrometry. The protein's amino acid sequence consists of 111 amino acids, rich in acidic residues, with an estimated pI of 3.97 and a calculated molecular mass of 12.039 Da. The lectin has a lectin Type-H domain architecture, belonging to the GalNAc and/or galactose binding family, and oligosaccharides with Gal/GalNAc residues. The highly conserved domain signature sequence in this family was identified in CiL-2 with a few modifications also observed in other algae lectins related to the group. The threedimensional structure and carbohydrate-binding site were predicted and analyzed using structural bioinformatics tools, revealing that CiL-2 exhibits a typical Type-H lectin structure, consisting of a β-sandwich with two antiparallel β-sheets, and a classic hexamer oligomerization state observed in the main representatives of the group. CiL-2 monosaccharidebinding site contained all the amino acids interacting with ligands conserved in this lectin family for a monomer. An extended site common in lectins of algal origin was also observed, likely used to accommodate polysaccharides and glycoproteins with GalNAc residues. The predicted molecular function, biological process, and protein location indicate that CiL-2 is a typical Type-H lectin, emphasizing its specificity for GalNAc and its ability to perform various functions in the cell. CiL-2 is a molecule with antimicrobial potential in combination with the antibiotic tetracycline, showing synergy against Staphylococcus aureus strains. Therefore, this study contributes to establishing CiL-2 as a new macroalga lectin with a determined primary structure, aiding in the understanding and functional and phylogenetic classification of lectins from these organisms.