Structural and Functional Characterization of New Lipid Transfer Proteins with Chitin-Binding Properties: Insights from Protein Structure Prediction, Molecular Docking, and Antifungal Activity.

Faced with the emergence of multiresistant microorganisms that affect human health, microbial agents have become a serious global threat, affecting human health and plant crops. Antimicrobial peptides have attracted significant attention in research for the development of new microbial control agents. This work's goal was the structural characterization and analysis of antifungal activity of chitin-binding peptides from Capsicum baccatum and Capsicum frutescens seeds on the growth of Candida and Fusarium species. Proteins were initially submitted to extraction in phosphate buffer pH 5.4 and subjected to chitin column chromatography. Posteriorly, two fractions were obtained for each species, Cb-F1 and Cf-F1 and Cb-F2 and Cf-F2, respectively. The Cb-F1 (C. baccatum) and Cf-F1 (C. frutescens) fractions did not bind to the chitin column. The electrophoresis results obtained after chromatography showed two major protein bands between 3.4 and 14.2 kDa for Cb-F2. For Cf-F2, three major bands were identified between 6.5 and 14.2 kDa. One band from each species was subjected to mass spectrometry, and both bands showed similarity to nonspecific lipid transfer protein. Candida albicans and Candida tropicalis had their growth inhibited by Cb-F2. Cf-F2 inhibited the development of C. albicans but did not inhibit the growth of C. tropicalis. Both fractions were unable to inhibit the growth of Fusarium species. The toxicity of the fractions was tested in vivo on Galleria mellonella larvae, and both showed a low toxicity rate at high concentrations. As a result, the fractions have enormous promise for the creation of novel antifungal compounds.

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.

Structural study and antimicrobial and wound healing effects of lectin from Solieria filiformis (Kützing) P.W.Gabrielson.

The SfL-1 isoform from the marine red algae Solieria filiformis was produced in recombinant form (rSfL-1) and showed hemagglutinating activity and inhibition similar to native SfL. The analysis of circular dichroism revealed the predominance of ß-strands structures with spectra of ßI-proteins for both lectins, which had Melting Temperature (Tm) between 41 °C and 53 °C. The three-dimensional structure of the rSfL-1 was determined by X-ray crystallography, revealing that it is composed of two ß-barrel domains formed by five antiparallel ß chains linked by a short peptide between the ß-barrels. SfL and rSfL-1 were able to agglutinate strains of Escherichia coli and Staphylococcus aureus and did not show antibacterial activity. However, SfL induced a reduction in E. coli biomass at concentrations from 250 to 125 µg mL-1, whereas rSfL-1 induced reduction in all concentrations tested. Additionally, rSfL-1 at concentrations from 250 to 62.5 µg mL-1, showed a statistically significant reduction in the number of colony-forming units, which was not noticed for SfL. Wound healing assay showed that the treatments with SfL and rSfL-1 act in reducing the inflammatory response and in the activation and proliferation of fibroblasts by a larger and fast deposition of collagen.

Trypsin/α-Amylase Inhibitors from Capsicum chinense Seeds: Characterization and Antifungal Activity against Fungi of Agronomic Importance.

BACKGROUND: Protease inhibitors (PIs) have attracted attention due to their important roles in plant defense. OBJECTIVE: The objective of this work was to characterize and evaluate the antimicrobial activity of the peptides of a family of serine PIs from Capsicum chinense Jacq. seeds. METHODS: Initially, PIs were extracted from the seeds and subjected to purification by chromatography, resulting in three different peptide enriched fractions (PEFs) termed PEF1, PEF2 and PEF3. Subsequently, the PEF3 was subjected to trypsin inhibition assays, α-amylase activity assays, antimicrobial activity assays on phytopathogenic fungi, and assays to determine the likely mechanisms of action. RESULTS: The PEF3 was composed of three protein bands with molecular masses ranging between 6 and 14 kDa. The amino acid residues of the ~6 kDa band showed high similarity with serine PIs. PEF3 inhibited the activity of the enzymes trypsin, human salivary α-amylase, and Tenebrio molitor larval α-amylase and inhibited the growth of phytopathogenic fungi, showing 83.7% loss of viability in Fusarium oxysporum. PEF3 induced reactive oxygen species in Colletotrichum lindemuthianum and F. oxysporum to dissipate their mitochondrial membrane potential and activated caspases in C. lindemuthianum. CONCLUSION: Our results reinforce the importance of PIs in plant defense mechanisms against phytopathogenic fungi as well as in their biotechnological applications for the control of plant pathogens.

Inhibition of Serine Protease, α-Amylase and Growth of Phytopathogenic Fungi by Antimicrobial Peptides from Capsicum chinense Fruits.

Plant fungal diseases cause major problems for the global economy. Antimicrobial peptides have aroused great interest in the control of phytopathogens, as they are natural molecules and have a broad spectrum of inhibitory activity. Herein, we have tried to identify and characterize antimicrobial peptides present in fruits of Capsicum chinense and to evaluate their enzymatic and antifungal activities. The retained fraction obtained in the anion exchange chromatography with strong antifungal activity was subjected to molecular exclusion chromatography and obtained four fractions named G1, G2, G3, and G4. The 6.0-kDa protein band of G2 showed similarity with protease inhibitors type II, and it was able to inhibit 100% of trypsin and α-amylase activities. The protein band with approximately 6.5 kDa of G3 showed similarity with sequences of protease inhibitors from genus Capsicum and showed growth inhibition of 48% for Colletotrichum lindemuthianum, 49% for Fusarium lateritium, and 51% for F. solani and F. oxysporum. Additionally, G3 causes morphological changes, membrane permeabilization, and ROS increase in F. oxysporum cells. The 9-kDa protein band of G4 fraction was similar to a nsLTP type 1, and a protein band of 6.5 kDa was similar to a nsLTP type 2. The G4 fraction was able to inhibit 100% of the activities of glycosidases tested and showed growth inhibition of 35 and 50% of F. oxysporum and C. lindemuthianum, respectively. C. chinense fruits have peptides with antifungal activity and enzyme inhibition with biotechnological potential.

Codium isthmocladum lectin 1 (CiL-1): Interaction with N-glycans explains antinociceptive and anti-inflammatory activities in adult zebrafish (Danio rerio).

Inflammation and oxidative stress are processes associated with different human diseases. They are treated using drugs that have several side effects. Seaweed are sources of potentially relevant natural compounds for use as treatment of these disorders. Lectins are able to reversibly interact with complex carbohydrates and modulate cell membrane glycosylated receptors through this interaction. This study aimed to determine the antinociceptive and anti-inflammatory potential of CiL-1 in adult zebrafish by modulation of TRPA1 through lectin-glycan binding. Possible neuromodulation by TRPA1 channel was also evaluated by camphor pretreatment. CiL-1 was efficacious at all tested doses, revealing anti-nociceptive and anti-inflammatory effects in adult zebrafish. This galactose-binding lectin was also able to reduce the content of ROS in brain and liver. In silico analyses showed CiL-1 interactions with both ligands tested. LacNac2 presents the most favorable binding energy with the protein. The interaction occurs at 4 subsites as an extended conformation at the site. LacNac2-Sia had a less favorable curved-shape interaction energy. Based on the predictions made for the oligosaccharides, a tetra-antenate putative glycan was schematically constructed, illustrating an interaction between TRPA1 N-glycan and CiL-1. This binding seems to be related to CiL-1 anti-inflammatory activity as result of receptor modulation.

Structural characterization of a galectin isolated from the marine sponge Chondrilla caribensis with leishmanicidal potential.

BACKGROUND: Solving primary structure of lectins leads to an understanding of the physiological roles within an organism and its biotechnological potential. Only eight sponge lectins have had their primary structure fully determined. METHODS: The primary structure of CCL, Chondrilla caribensis lectin, was determined by tandem mass spectrometry. The three-dimensional structure was predicted and the protein-carbohydrate interaction analysed by molecular docking. Furthermore, the anti-leishmanial activity was observed by assays with Leishmania infantum. RESULTS: The amino acid sequence consists of 142 amino acids with a calculated molecular mass of 15,443 Da. The lectin has a galectin-like domain architecture. As observed in other sponge galectins, the signature sequence of a highly conserved domain was also identified in CCL with some modifications. CCL exhibits a typical galectin structure consisting of a ß-sandwich. Molecular docking showed that the amino acids interacting with CCL ligands at the monosaccharide binding site are mostly the same as those conserved in this family of lectins. Through its interaction with L. infantum glycans, CCL was able to inhibit the development of this parasite. CCL also induced apoptosis after eliciting ROS production and altering the membrane integrity of Leishmania infantum promastigote. CONCLUSIONS: CCL joins the restricted group of sponge lectins with determined primary structure and very high biotechnological potential owing to its promising results against pathogens that cause Leishmaniasis. GENERAL SIGNIFICANCE: As the determination of primary structure is important for biological studies, now CCL can become a sponge galectin with an exciting future in the field of human health.

Antibacterial activity of a new lectin isolated from the marine sponge Chondrilla caribensis.

A new lectin from the marine sponge Chondrilla caribensis (CCL) was isolated by affinity chromatography in Sepharose 6B media. CCL is a homotetrameric protein formed by subunits of 15,445 ±2Da. The lectin showed affinity for disaccharides containing galactose and mucin. Mass spectrometric analysis revealed about 50% of amino acid sequence of CCL, which showed similarity with a lectin isolated from Aplysina lactuca. Secondary structure consisted of 10% α-helix, 74% ß-sheet/ß-turn and 16% coil, and this profile was unaltered in a broad range of pH and temperatures. CCL agglutinated Staphylococcus aureus, S epidermidis and Escherichia coli, and it was able to reduce biofilm biomass, but showed no inhibition of planktonic growth of these bacteria. CCL activity was inhibited by α-lactose, indicating that Carbohydrate Recognition Domain (CRD) of the lectin was involved in antibiofilm activity.

Structural characterization of two isolectins from the marine red alga Solieria filiformis (Kützing) P.W. Gabrielson and their anticancer effect on MCF-7 breast cancer cells.

As described in the literature, Solieria filiformis lectin (SfL) from the marine red alga S. filiformis was found to have antinociceptive and anti-inflammatory effects. In this study, we characterized two SfL variants, SfL-1 and SfL-2, with molecular mass of 27,552Da and 27,985Da, respectively. The primary structures of SfL-1 and SfL-2 consist of four tandem-repeat protein domains with 67 amino acids each. SfL-1 and -2 showed high similarity to OAAH-family lectins. 3D structure prediction revealed that SfL-1 and -2 are composed of two ß-barrel-like domains formed by five antiparallel ß-strands, which are connected by a short peptide linker. Furthermore, the mixture of isoforms (SfLs) showed anticancer effect against MCF-7 cells. Specifically, SfLs inhibited 50% of viability in MCF-7 cells after treatment at 125µg.mL-1, while the inhibition of Human Dermal Fibroblasts (HDF) was 34% with the same treatment. Finally, 24h after treatment, 25% of MCF-7 cells were in early apoptosis and 35% in late apoptosis. Evaluation of pro- and anti-apoptotic gene expression of MCF-7 cells revealed that SfLs induced caspase-dependent apoptosis within 24h.

Isolation, biochemical characterization and antibiofilm effect of a lectin from the marine sponge Aplysina lactuca.

A new lectin was isolated from the marine sponge Aplysina lactuca (ALL) by combining ammonium sulfate precipitation and affinity chromatography on guar gum matrix. ALL showed affinity for the disaccharides α-lactose, ß-lactose and lactulose (Ka=12.5, 31.9 and 145.5M-1, respectively), as well as the glycoprotein porcine stomach mucin. Its hemagglutinating activity was stable in neutral acid pH values and temperatures below 60°C. ALL is a dimeric protein formed by two covalently linked polypeptide chains. The average molecular mass, as determined by Electrospray Ionization Mass Spectrometry (ESI-MS), was 31,810±2Da. ESI-MS data also indicated the presence of three cysteines involved in one intrachain and one interchain disulfide bond. The partial amino acid sequence of ALL was determined by tandem mass spectrometry. Eight tryptic peptides presented similarity with lectin I isolated from Axinella polypoides. Its secondary structure is predominantly ß-sheet, as indicated by circular dichroism (CD) spectroscopy. ALL agglutinated gram-positive and gram-negative bacterial cells, and it were able to significantly reduce the biomass of the bacterial biofilm tested at dose- dependent effect.

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.

H-3, a new lectin from the marine sponge Haliclona caerulea: purification and mass spectrometric characterization.

A new lectin from the marine sponge Haliclona caerulea (H-3) was isolated using a combination of hydrophobic interaction chromatography and ion-exchange chromatography. H-3 is a protein with three distinct bands on SDS-PAGE: 9 kDa, 16 kDa and 18 kDa. Nevertheless, on gel filtration and N-PAGE, H-3 showed a symmetrical peak and a unique band, respectively. Hemagglutinating activity of H-3 was stable at neutral pH and temperatures up to 60 °C. N-Acetylgalactosamine and porcine stomach mucin were the most potent inhibitors of H-3. Primary structure of the lectin was determined using tandem mass spectrometry, and it showed no similarity to any members of the animal lectin families. Top down fragmentation revealed some posttranslational modifications in H-3, including glycosylation. The glycan composition of H-3 was determined, and its structure was predicted. Furthermore, H-3 is a blue protein, binding to a chromophore(-597) by weak interactions, and this is the first time that the interaction between one lectin and a natural chromophore has been shown.