An Update of Lectins from Marine Organisms: Characterization, Extraction Methodology, and Potential Biofunctional Applications

A novel lectin with a distinct Gal_Lectin and CUB domain mediates haemocyte phagocytosis in oyster Crassostrea gigas

Invertebrate lectins exhibit structural diversity and play crucial roles in the innate immune responses by recognizing and eliminating pathogens. In the present study, a novel lectin containing a Gal_Lectin, a CUB and a transmembrane domain was identified from the Pacific oyster Crassostrea gigas (defined as CgGal-CUB). CgGal-CUB mRNA was detectable in all the examined tissues with the highest expression in adductor muscle (11.00-fold of that in haemocytes, p < 0.05). The expression level of CgGal-CUB mRNA in haemocytes was significantly up-regulated at 3, 24, 48 and 72 h (8.37-fold, 12.13-fold, 4.28-fold and 10.14-fold of that in the control group, respectively) after Vibrio splendidus stimulation. The recombinant CgGal-CUB (rCgGal-CUB) displayed binding capability to Mannan (MAN), peptidoglycan (PGN), D-(+)-Galactose and L-Rhamnose monohydrate, as well as Gram-negative bacteria (Escherichia coli, V. splendidus and Vibrio anguillarum), Gram-positive bacteria (Micrococcus luteus, Staphylococcus aureus, and Bacillus sybtilis) and fungus (Pichia pastoris). rCgGal-CUB was also able to agglutinate V. splendidus, and inhibit V. splendidus growth. Furthermore, rCgGal-CUB exhibited the activities of enhancing the haemocyte phagocytosis towards V. splendidus, and the phagocytosis rate of haemocytes was descended in blockage assay with CgGal-CUB antibody. These results suggested that CgGal-CUB served as a pattern recognition receptor to bind various PAMPs and bacteria, and enhanced the haemocyte phagocytosis towards V. splendidus.

Effects of chilling and cryoprotectants on glycans in shrimp embryos

Glycans are carbohydrates present in every organism that bind to specific molecules such as lectins, a diverse group of proteins. Glycans are vital to cell proliferation and protein trafficking. In addition, embryogenesis is a critical phase in the development of marine organisms. This study investigated the effects of chilling and cryoprotective agents (CPAs) on glycans in the embryos of Stenopus hispidus. The glycan profiles of embryos of S. hispidus at the heartbeat stage were analyzed using lectin arrays. The results of analyses revealed that mannose was the most abundant glycan in the S. hispidus embryos; mannose is crucial to cell proliferation, providing the energy required for embryonic growth. Additionally, the results reveled that chilling altered the content of several glycans, including fucose and Gla-GlcNAc. Chilling may promote monosaccharide accumulation, facilitating osmotic regulation of cells and signal molecules to aid S. hispidus embryos in adapting to cold conditions. Changes were also observed in the lectins NPA, orysata, PALa, ASA, discoidin II, discoidin I, UDA, PA-IIL, and PHA-P after the samples were treated with different CPAs. DMSO may minimize cell damage during exposure to chilling by preserving cell structures, membrane properties, and functions. The present study is the first to investigate the profiles and functions of glycans in shrimp embryos subjected to low-temperature injuries. This study enhances the understanding of cell reproduction during embryogenesis and provides valuable information for the study of glycans in embryos.

Potential Involvement of the South American Lungfish Intelectin-2 in Innate-Associated Immune Modulation

Intelectins belong to a family of lectins with specific and transitory carbohydrate interaction capabilities. These interactions are related to the activity of agglutinating pathogens, as intelectins play a significant role in immunity. Despite the prominent immune defense function of intelectins, limited information about its structural characteristics and carbohydrate interaction properties is available. This study investigated an intelectin transcript identified in RNA-seq data obtained from the South American lungfish (Lepidosiren paradoxa), namely LpITLN2-B. The structural analyses predicted LpITLN2-B to be a homo-trimeric globular protein with the fibrinogen-like functional domain (FReD), exhibiting a molecular mass of 57 kDa. The quaternary structure is subdivided into three monomers, A, B, and C, and each domain comprises 11 β-sheets: an anti-parallel β-sheet, a β-hairpin, and a disordered β-sheet structure. Molecular docking demonstrates a significant interaction with disaccharides rather than monosaccharides. The preferential interaction with disaccharides highlights the potential interaction with pathogen molecules, such as LPS and Poly(I:C). The hemagglutination assay inhibited lectins activity, especially maltose and sucrose, highlighting lectin activity in L. paradoxa samples. Overall, our results show the potential relevance of LpITLN2-B in L. paradoxa immune defense against pathogens.

Unlocking the Therapeutic Potential of a Manila Clam-Derived Antioxidant Peptide: Insights into Mechanisms of Action and Cytoprotective Effects against Oxidative Stress

Reactive oxygen species (ROS) are implicated in various pathological conditions due to their ability to induce oxidative damage to cellular components. In this study, we investigated the antioxidant properties of a peptide isolated from the hydrolysate of Manila clam (Ruditapes philippinarum) muscle. Purification steps yielded RPTE2-2-4, exhibiting potent scavenging activities against DPPH•, HO•, and O2•-, akin to Vitamin C. Structural analysis showed that the isolated peptide, LFKKNLLTL, exhibited characteristics associated with antioxidant activity, including a short peptide length and the presence of aromatic and hydrophobic amino acid residues. Moreover, our study demonstrated the cytoprotective effects of the peptide against H2O2-induced oxidative stress in HepG2 cells. Pretreatment with the peptide resulted in a dose-dependent reduction in intracellular ROS levels and elevation of glutathione (GSH) levels, indicating its ability to modulate cellular defense mechanisms against oxidative damage. Furthermore, the peptide stimulated the expression of the cytoprotective enzyme heme oxygenase-1 (HO-1), further reinforcing its antioxidant properties. Overall, our findings highlight the potential of the Manila clam-derived peptide as a natural antioxidant agent with therapeutic implications for oxidative stress-related diseases. Further investigation into its mechanisms of action and in vivo efficacy is warranted to validate its therapeutic potential.

Largemouth bass galectin, MsGal-9: Mediating various functions as a pattern recognition receptor and a potential damage-associated molecular pattern

Galectins are lectins that bind to β-galactose and are widely expressed in immune system tissues, playing pivotal roles in innate immunity through their conserved carbohydrate-recognition domains (CRDs). In this present investigation, a tandem-repeat galectin was discovered in the largemouth bass, Micropterus salmoides (designated as MsGal-9). The open reading frame of MsGal-9 encodes two CRDs, each containing two consensus motifs that are essential for ligand binding. MsGal-9 is expressed in various tissues of the largemouth bass, with particularly high expression levels in the liver and spleen. The full-length form of MsGal-9, as well as the N-terminal (MsGal-9-N) and C-terminal (MsGal-9-C) CRDs, were individually recombined. Their ability for nonself recognition was studied. The three recombinant proteins were able to bind to glucan (GLU), peptidoglycan (PGN), and lipopolysaccharide (LPS), with MsGal-9 displaying the highest binding activity. Furthermore, rMsGal-9-N exhibited higher binding activity towards GLU in comparison to rMsGal-9-C. Further investigations revealed that the full-length rMsGal-9 could significantly bind to Gram-positive bacteria, Gram-negative bacteria, and fungi, while rMsGal-9-C specifically bound to Escherichia coli. However, rMsGal-9-N did not exhibit significant binding activity towards any microbes. These findings indicate that MsGal-9 requires both CRDs to cooperate in order to fulfill its nonself recognition function. All three recombinant proteins demonstrated agglutination activity towards various microbes, with MsGal-9 and MsGal-9-N displaying a similar broad binding spectrum, while MsGal-9-C agglutinated three types of bacteria. Moreover, both MsGal-9 and MsGal-9-N were capable of coagulating largemouth bass red blood cells, whereas MsGal-9-C lacked this ability. However, MsGal-9-C played a significant role in enhancing the encapsulation of leukocytes in comparison to MsGal-9-N. All three proteins acted as potential damage-associated molecular patterns (DAMPs), inducing apoptosis in leukocytes.

Physicochemical properties and antimicrobial activities of MytiLec-1, a member from the mytilectin family of mussels

MytiLec-1, the recombinant form of a mussel lectin from Mytillus galloprovincialis, was purified by affinity chromatography and showed the maximum hemagglutination activity at a temperature range of 10 °C to 40 °C and at pH 7.0 to 9.0. Denaturants like urea and acidic-guanidine inhibited its hemagglutination activity significantly. MytiLec-1 was found to be metal-independent though Ca2+ slightly increased the activity of chelated MytiLec-1. The lectin suppressed 65 % growth of Pseudomonas aeruginosa (ATCC 47085) at 200 μg/ml and reduced the formation of biofilm (15 % at 200 μg/ml). Comparing to Shigella sonnei (ATCC 29930), Shigella boydii (ATCC 231903) and Shigella dysenteriae (ATCC 238135), Bacillus cereus (ATCC 14579) was slightly more sensitive to MytiLec-1. At a concentration of 200 μg/disc and 100 μg/ml, MytiLec-1 prevented the growth of Aspergillus niger and agglutinated the spores of Aspergillus niger and Trichoderma reesei, respectively. Amino acid sequences, physicochemical properties and antimicrobial activities of MytiLec-1 were compared with three other lectins (CGL, MTL and MCL from Crenomytilus grayanus, Mytilus trossulas and Mytilus californianus, respectively) from the mytilectin family of bivalve mollusks. It reconfirms the function of these lectins to recognize pathogens and perform important roles in innate immune response of mussels.

New l-Rhamnose-Binding Lectin from the Bivalve Glycymeris yessoensis: Purification, Partial Structural Characterization and Antibacterial Activity

In this study, a new l-rhamnose-binding lectin (GYL-R) from the hemolymph of bivalve Glycymeris yessoensis was purified using affinity and ion-exchange chromatography and functionally characterized. Lectin antimicrobial activity was examined in different ways. The lectin was inhibited by saccharides possessing the same configuration of hydroxyl groups at C-2 and C-4, such as l-rhamnose, d-galactose, lactose, l-arabinose and raffinose. Using the glycan microarray approach, natural carbohydrate ligands were established for GYL-R as l-Rha and glycans containing the α-Gal residue in the terminal position. The GYL-R molecular mass determined by MALDI-TOF mass spectrometry was 30,415 Da. The hemagglutination activity of the lectin was not affected by metal ions. The lectin was stable up to 75 °C and between pH 4.0 and 12.0. The amino acid sequence of the five GYL-R segments was obtained with nano-ESI MS/MS and contained both YGR and DPC-peptide motifs which are conserved in most of the l-rhamnose-binding lectin carbohydrate recognition domains. Circular dichroism confirmed that GYL is a α/β-protein with a predominance of the random coil. Furthermore, GYL-R was able to bind and suppress the growth of the Gram-negative bacteria E. coli by recognizing lipopolysaccharides. Together, these results suggest that GYL-R is a new member of the RBL family which participates in the self-defense mechanism against bacteria and pathogens with a distinct carbohydrate-binding specificity.

Diverse Transcriptome Responses to Salinity Change in Atlantic Cod Subpopulations

Adaptation to environmental variation caused by global climate change is a significant aspect of fisheries management and ecology. A reduction in ocean salinity is visible in near-shore areas, especially in the Baltic Sea, where it is affecting the Atlantic cod population. Cod is one of the most significant teleost species, with high ecological and economical value worldwide. The population of cod in the Baltic Sea has been traditionally divided into two subpopulations (western and eastern) existing in higher- and lower-salinity waters, respectively. In recent decades, both Baltic cod subpopulations have declined massively. One of the reasons for the poor condition of cod in the Baltic Sea is environmental factors, including salinity. Thus, in this study, an oligonucleotide microarray was applied to explore differences between Baltic cod subpopulations in response to salinity fluctuations. For this purpose, an exposure experiment was conducted consisting of salinity elevation and reduction, and gene expression was measured in gill tissue. We found 400 differentially expressed genes (DEGs) involved in the immune response, metabolism, programmed cell death, cytoskeleton, and extracellular matrix that showed a subpopulation-dependent pattern. These findings indicate that osmoregulation in Baltic cod is a complex process, and that western and eastern Baltic cod subpopulations respond differently to salinity changes.

Molecular cloning, expression, and functional analysis of a putative lectin from the pearl oyster (Pinctada fucata, Gould 1850)

Marine lectins are a group of proteins that possess specific carbohydrate recognition and binding domains. They exhibit various activities, including antimicrobial, antitumor, antiviral, and immunomodulatory effects. In this study, a novel galectin-binding lectin gene named PFL-96 (GenBank: OQ561753.1) was cloned from Pinctada fucata. The PFL-96 gene has an open reading frame of 324 base pairs (bp) and encodes a protein comprising 107 amino acids. The protein has a molecular weight of 11.95 kDa and an isoelectric point of 9.27. It contains an N-terminal signal peptide and a galactose-binding lectin domain. The sequence identity to lectin proteins from fish, echinoderms, coelenterates, and shellfish ranges from 31.90 to 40.00 %. In the phylogenetic analysis, it was found that the PFL-96 protein is closely related to the lectin from Pteria penguin. The PFL-96 recombinant protein exhibited coagulation activity on 2 % rabbit red blood cells at a concentration of ≥8 μg/mL. Additionally, it showed significant hemolytic activity at a concentration of ≥32 μg/mL. The PFL-96 recombinant protein exhibited significant antibacterial activity against Bacillus subtilis, Staphylococcus aureus, Candida albicans, and Vibrio alginolyticus, with minimum inhibitory concentrations (MIC) of 4, 8, 16, and 16 μg/mL, respectively. The minimum bactericidal concentrations (MBC) were determined to be 8, 16, 32, and 32 μg/mL, respectively. Furthermore, the PFL-96 recombinant protein exhibited inhibitory effects on the proliferation of Hela tumor cells, HepG2 tumor cells, and C666-1 tumor cells, with IC50 values of 7.962, 8.007, and 9.502 μg/mL, respectively. These findings suggest that the recombinant protein PFL-96 exhibits significant bioactivity in vitro, contributing to a better understanding of the active compounds found in P. fucata. The present study establishes a fundamental basis for further investigation into the mechanism of action and structural optimization of the recombinant protein PFL-96. The aim is to develop potential candidates for antibacterial and anti-tumor agents.

Invertebrate C1q Domain-Containing Proteins: Molecular Structure, Functional Properties and Biomedical Potential

C1q domain-containing proteins (C1qDC proteins) unexpectedly turned out to be widespread molecules among a variety of invertebrates, despite their lack of an integral complement system. Despite the wide distribution in the genomes of various invertebrates, data on the structure and properties of the isolated and characterized C1qDC proteins, which belong to the C1q/TNF superfamily, are sporadic, although they hold great practical potential for the creation of new biotechnologies. This review not only summarizes the current data on the properties of already-isolated or bioengineered C1qDC proteins but also projects further strategies for their study and biomedical application. It has been shown that further broad study of the carbohydrate specificity of the proteins can provide great opportunities, since for many of them only interactions with pathogen-associated molecular patterns (PAMPs) was evaluated and their antimicrobial, antiviral, and fungicidal activities were studied. However, data on the properties of C1qDC proteins, which researchers originally discovered as lectins and therefore studied their fine carbohydrate specificity and antitumor activity, intriguingly show the great potential of this family of proteins for the creation of targeted drug delivery systems, vaccines, and clinical assays for the differential diagnosis of cancer. The ability of invertebrate C1qDC proteins to recognize patterns of aberrant glycosylation of human cell surfaces and interact with mammalian immunoglobulins indicates the great biomedical potential of these molecules.

Oral vaccination with recombinant Lactobacillus casei with surface displayed OmpK fused to CTB as an adjuvant against Vibrio mimicus infection in Carassius auratus

Vibrio mimicus (V. mimicus) is a pathogenic bacterium that causes diseases in humans and various aquatic animals. A particularly efficient way to provide protection against V. mimicus is through vaccination. However, there are few commercial vaccines against V. mimics, especially oral vaccines. In our study, two surface-display recombinant Lactobacillus casei (L. casei) Lc-pPG-OmpK and Lc-pPG-OmpK-CTB were constructed using L. casei ATCC393 as an antigen delivery vector, outer membrane protein K (OmpK) of V. mimicus as an antigen, and cholera toxin B subunit (CTB) as a molecular adjuvant; furthermore, the immunological effects of recombinant L.casei in Carassius auratus (C. auratus) were assessed. The results indicated that oral recombinant L.casei Lc-pPG-OmpK and Lc-pPG-OmpK-CTB stimulated higher levels of serum-specific immunoglobulin M (IgM) and increased the activity of acid phosphatase (ACP), alkaline phosphatase (AKP), superoxide dismutase (SOD), lysozyme (LYS), lectin, C3, and C4 in C. auratus, compared with control groups (Lc-pPG group and PBS group). Furthermore, the expression of interleukin-1β (IL-1β), interleukin-10 (IL-10), tumor necrosis factor-α (TNF-α), and transforming growth factor-β (TGF-β) in the liver, spleen, head kidney, hind intestine and gills of C. auratus was significantly increased, compared with that in the controls. These results demonstrated that the two recombinant L. casei strains could effectively trigger humoral and cellular immunity in C. auratus. In addition, two recombinant L.casei strains were able to survive and colonize the intestine of C. auratus. Importantly, after being challenged with V. mimicus, C. auratus fed Lc-pPG-OmpK and Lc-pPG-OmpK-CTB exhibited greater survival rates than the controls (52.08% and 58.33%, respectively). The data showed that recombinant L. casei could elicit a protective immunological response in C. auratus. The effect of the Lc-pPG-OmpK-CTB group was better than that of the Lc-pPG-OmpK group, and Lc-pPG-OmpK-CTB was found to be an effective candidate for oral vaccination.

Multiomic Approach for Bioprospection: Investigation of Toxins and Peptides of Brazilian Sea Anemone Bunodosoma caissarum

Sea anemones are sessile invertebrates of the phylum Cnidaria and their survival and evolutive success are highly related to the ability to produce and quickly inoculate venom, with the presence of potent toxins. In this study, a multi-omics approach was applied to characterize the protein composition of the tentacles and mucus of Bunodosoma caissarum, a species of sea anemone from the Brazilian coast. The tentacles transcriptome resulted in 23,444 annotated genes, of which 1% showed similarity with toxins or proteins related to toxin activity. In the proteome analysis, 430 polypeptides were consistently identified: 316 of them were more abundant in the tentacles while 114 were enriched in the mucus. Tentacle proteins were mostly enzymes, followed by DNA- and RNA-associated proteins, while in the mucus most proteins were toxins. In addition, peptidomics allowed the identification of large and small fragments of mature toxins, neuropeptides, and intracellular peptides. In conclusion, integrated omics identified previously unknown or uncharacterized genes in addition to 23 toxin-like proteins of therapeutic potential, improving the understanding of tentacle and mucus composition of sea anemones.

Structural and functional analysis of a tandem repeat galacturonic acid-binding lectin from the sea hare Aplysia californica

A d-galacturonic acid-specific lectin, named AcL, was purified from the sea hare Aplysia californica by galactose-agarose affinity chromatography. AcL has a molecular mass of 27.5 kDa determined by MALDI-TOF mass spectrometry. This lectin shows a good affinity for d-galacturonic acid and a lower affinity for galactosides: raffinose, melibiose, α and β-lactose, and d-galactose. We determined the amino acid sequence of AcL by trypsin digestion and subsequent peptide analysis by mass spectrometry, resulting in a 238 amino acid protein with a theoretical molecular mass of 26.4 kDa. The difference between the theoretical and experimental values can be attributed to post-translational modifications. Thiol-disulfide quantification discerned five disulfide bonds and three free cysteines. The structure of Acl is mainly comprised of beta sheets, determined by circular dichroism, and predicted with AlphaFold. Theoretical models depict three nearly identical tandem domains consisting of two beta sheets each. From docking analysis, we identified AcL glycan-binding sites as multiple conserved motifs in each domain. Furthermore, phylogenetic analysis based on its structure and sequence showed that AcL and its closest homologues (GalULs) form a clear monophyletic group, distinct from other glycan-binding proteins with a jelly-roll fold: lectins of types F and H. GalULs possess four conserved sequence regions that distinguish them and are either ligand-binding motifs or stabilizing network hubs. We suggest that this new family should be referred to as GalUL or D-type, following the traditional naming of lectins; D standing for depilans, the epithet for the species (Aplysia depilans) from which a lectin of this family was first isolated and described.