Purificação, caracterização bioquímica, estrutural e atividade antibacteriana de uma galectina da esponja marinha Aiolochroia crassa (Hyatt, 1875)

Abstract

Sponges are organisms belonging to the phylum Porifera and produce a diverse arsenal of active biomolecules important to the pharmaceutical industry, as they can exhibit antimicrobial, antiviral, anti-inflammatory, antimitotic, and other activities. Among these molecules are lectins. Lectins are proteins or glycoproteins that reversibly bind to mono- or oligosaccharides. The species Aiolochroia crassa belongs to the class Desmospongiae and shows broad potential in the production of compounds that could be used as biomedical tools. The aim of this study was to purify a lectin from A. crassa, determine the biochemical and structural characteristics of the isolated lectin, and evaluate its antimicrobial effects in inhibiting bacterial biofilms and in combination with antibiotics. The lectin from Aiolochroia crassa (AcrL) was purified through ammonium sulfate precipitation followed by affinity chromatography on a Sepharose 4B matrix. In SDS-PAGE, the new lectin is a monomer of approximately 15 kDa. In the hemagglutination activity assay, the protein was stable in neutral-alkaline pH and at temperatures below 70ºC. The hemagglutination activity of AcrL was inhibited by PSM type II and III glycoproteins, fetuin, BSM, and asialofetuin. In the isothermal calorimetry (ITC) study, the lectin showed high affinity for the glycoprotein fetuin with a Ka of 3039x104 M-1 . In MS/MS amino acid sequencing, AcrL has 146 amino acids with a combined molecular mass of 16,201 Da. This protein has an amino acid sequence containing conserved residues typical of the galectin family. The secondary structure prediction of AcrL by circular dichroism showed that the protein is composed of 4% α-helix, 40% β-sheet, 22% β-turns, and 34% random structures, with a melting temperature determined at 84.5ºC. The three-dimensional structure prediction of AcrL showed that the lectin is composed of a typical galectin β-sandwich, with two antiparallel β-sheets consisting of five strands each. AcrL was able to agglutinate and significantly reduce biofilms of bacterial strains of Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli. Additionally, when combined with the antibiotics ampicillin, tetracycline, and oxacillin, it showed synergistic and/or additive activity against S. aureus and S. epidermidis. Thus, a new protein was isolated, and the presented results will serve as a basis for biotechnological application in a biological model against pathogenic bacteria.