Isolation and characterization of a sex-specific lectin in a marine red alga, Aglaothamnion oosumiense Itono

Exploring the Structural Diversity and Biotechnological Potential of the Rhodophyte Phycolectome

Lectins are non-covalent glycan-binding proteins found in all living organisms, binding specifically to carbohydrates through glycan-binding domains. Lectins have various biological functions, including cell signaling, molecular recognition, and innate immune responses, which play multiple roles in the physiological and developmental processes of organisms. Moreover, their diversity enables biotechnological exploration as biomarkers, biosensors, drug-delivery platforms, and lead molecules for anticancer, antidiabetic, and antimicrobial drugs. Lectins from Rhodophytes (red seaweed) have been extensively reported and characterized for their unique molecular structures, carbohydrate-binding specificities, and important biological activities. The increasing number of sequenced Rhodophyte genomes offers the opportunity to further study this rich source of lectins, potentially uncovering new ones with properties significantly different from their terrestrial plant counterparts, thus opening new biotechnological applications. We compiled literature data and conducted an in-depth analysis of the phycolectomes from all Rhodophyta genomes available in NCBI datasets. Using Hidden Markov Models capable of identifying lectin-type domains, we found at least six different types of lectin domains present in Rhodophytes, demonstrating their potential in identifying new lectins. This review integrates a computational analysis of the Rhodophyte phycolectome with existing information on red algae lectins and their biotechnological potential.

Research progress in microalgae nutrients: emerging extraction and purification technologies, digestive behavior, and potential effects on human gut

Microalgae contain a diverse range of high-value compounds that can be utilized directly or fractionated to obtain components with even greater value-added potential. With the use of microalgae for food and medical purposes, there is a growing interest in their digestive properties and impact on human gut health. The extraction, separation, and purification of these components are key processes in the industrial application of microalgae. Innovative technologies used to extract and purify microalgal high-added-value compounds are key for their efficient utilization and evaluation. This review's comprehensive literature review was performed to highlight the main high-added-value microalgal components. The technologies for obtaining bioactive compounds from microalgae are being developed rapidly, various innovative, efficient, green separation and purification technologies are emerging, thus helping in the scaling-up and subsequent commercialization of microalgae products. Finally, the digestive behavior of microalgae nutrients and their health effects on the human gut microbiota were discussed. Microalgal nutrients exhibit favorable digestive properties and certain components have been shown to benefit gut microbes. The reality that must be faced is that multiple processes are still required for microalgae raw materials to final usable products, involving energy, time consumption and loss of ingredients, which still face challenges.

Red macroalgae in the genomic era

Rhodophyta (or red algae) are a diverse and species-rich group that forms one of three major lineages in the Archaeplastida, a eukaryotic supergroup whose plastids arose from a single primary endosymbiosis. Red algae are united by several features, such as relatively small intron-poor genomes and a lack of cytoskeletal structures associated with motility like flagella and centrioles, as well as a highly efficient photosynthetic capacity. Multicellular red algae (or macroalgae) are one of the earliest diverging eukaryotic lineages to have evolved complex multicellularity, yet despite their ecological, evolutionary, and commercial importance, they have remained a largely understudied group of organisms. Considering the increasing availability of red algal genome sequences, we present a broad overview of fundamental aspects of red macroalgal biology and posit on how this is expected to accelerate research in many domains of red algal biology in the coming years.

Hydrogen peroxide signalling mediates fertilization and post-fertilization development in the red alga Bostrychia moritziana

Reactive oxygen species (ROS) signalling has a multitude of roles in cellular processes throughout biology. We hypothesized that red algal fertilization may offer an interesting model to study ROS-mediated signalling, as the stages of fertilization are complex and unique. We detected the localization of ROS production microscopically and monitored the expression of three homologues of NADPH oxidase in reproductive cells during fertilization. ROS were instantaneously produced by spermatia (sperm) when they attached to female trichogynes, diffused across the cell membrane in the form of H2O2, and triggered ROS generation in the carpogonium (egg) as well as carpogonial branch cells which are not in direct contact with spermatia. The expression of NADPH oxidase homologues, RESPIRATORY BURST OXIDASE HOMOLOGUES (BmRBOHs), began to be up-regulated in the female plant upon gamete binding, peaking during the fertilization process and descending back to their original level after fertilization. Pre-treatment with diphenylene iodonium or caffeine blocked gene expression as well as H2O2 production. Post-fertilization development was also inhibited when the redox state of the plants was perturbed with H2O2 at any time before or after the fertilization. Our results suggest that H2O2 acts as an auto-propagating signalling molecule, possibly through Ca2+ channel activation, and regulates gene expression in fertilization as well as post-fertilization development in red algae.

Man-Specific, GalNAc/T/Tn-Specific and Neu5Ac-Specific Seaweed Lectins as Glycan Probes for the SARS-CoV-2 (COVID-19) Coronavirus

Seaweed lectins, especially high-mannose-specific lectins from red algae, have been identified as potential antiviral agents that are capable of blocking the replication of various enveloped viruses like influenza virus, herpes virus, and HIV-1 in vitro. Their antiviral activity depends on the recognition of glycoprotein receptors on the surface of sensitive host cells-in particular, hemagglutinin for influenza virus or gp120 for HIV-1, which in turn triggers fusion events, allowing the entry of the viral genome into the cells and its subsequent replication. The diversity of glycans present on the S-glycoproteins forming the spikes covering the SARS-CoV-2 envelope, essentially complex type N-glycans and high-mannose type N-glycans, suggests that high-mannose-specific seaweed lectins are particularly well adapted as glycan probes for coronaviruses. This review presents a detailed study of the carbohydrate-binding specificity of high-mannose-specific seaweed lectins, demonstrating their potential to be used as specific glycan probes for coronaviruses, as well as the biomedical interest for both the detection and immobilization of SARS-CoV-2 to avoid shedding of the virus into the environment. The use of these seaweed lectins as replication blockers for SARS-CoV-2 is also discussed.

Characterization of a Novel Mannose-Binding Lectin with Antiviral Activities from Red Alga, Grateloupia chiangii

Lectins have the ability to bind specific carbohydrates and they have potential applications as medical and pharmacological agents. The unique structure and usefulness of red algal lectin have been reported, but these lectins are limited to a few marine algal groups. In this study, a novel mannose-binding lectin from Grateloupia chiangii (G. chiangii lectin, GCL) was purified using antiviral screens and affinity chromatography. We characterized the molecular weight, agglutination activity, hemagglutination activity, and heat stability of GCL. To determine the carbohydrate specificity, a glycan microarray was performed. GCL showed strong binding affinity for Maltohexaose-β-Sp1 and Maltoheptaose-β-Sp1 with weak affinity for other monosaccharides and preferred binding to high-mannan structures. The N-terminal sequence and peptide sequence of GCL were determined using an Edman degradation method and LC-MS/MS, and the cDNA and peptide sequences were deduced. GCL was shown to consist of 231 amino acids (24.9 kDa) and the N-terminus methionine was eliminated after translation. GCL possessed a tandem repeat structure of six domains, similar to the other red algal lectins. The mannose binding properties and tandem repeat structure of GCL may confer it the potential to act as an antiviral agent for protection against viral infection.

Purification and partial characterization of a lectin protein complex, the clathrilectin, from the calcareous sponge Clathrina clathrus

Carbohydrate-binding proteins were purified from the marine calcareous sponge Clathrina clathrus via affinity chromatography on lactose and N-acetyl glucosamine-agarose resins. Proteomic analysis of acrylamide gel separated protein subunits obtained in reducing conditions pointed out several candidates for lectins. Based on amino-acid sequence similarity, two peptides displayed homology with the jack bean lectin Concanavalin A, including a conserved domain shared by proteins in the L-type lectin superfamily. An N-acetyl glucosamine - binding protein complex, named clathrilectin, was further purified via gel filtration chromatography, bioguided with a diagnostic rabbit erythrocyte haemagglutination assay, and its activity was found to be calcium dependent. Clathrilectin, a protein complex of 3200kDa estimated by gel filtration, is composed of monomers with apparent molecular masses of 208 and 180kDa estimated on 10% SDS-PAGE. Nine internal peptides were identified using proteomic analyses, and compared to protein libraries from the demosponge Amphimedon queenslandica and a calcareous sponge Sycon sp. from the Adriatic Sea. The clathrilectin is the first lectin isolated from a calcareous sponge and displays homologies with predicted sponge proteins potentially involved in cell aggregation and interaction with bacteria.

Functional recombinants designed from a fetuin/asialofetuin-specific marine algal lectin, rhodobindin

Plant lectins have attracted much attention for biomedical applications including targeted drug delivery system and therapy against tumors and microbial infections. The main problem of using lectins as a biomedical tool is a batch-to-batch variation in isoforms content. The production of lectins using recombination tools has the advantage of obtaining high amounts of proteins with more precise properties, but there are only a handful of functional recombinant lectins presently available. A fetuin/asialo-fetuin specific lectin, Rhodobindin, has unique tandem repeats structure which makes it useful in exploiting for recombinant lectin. We developed three functional recombinant lectins using E. coli expression system: one from full cDNA sequence and two from fragmentary sequences of Rhodobindin. Hemagglutinating activity and solubility of the recombinant lectins were highest at OD 0.7 cell concentration at 20 °C. The optimized process developed in this study was suitable for the quality-controlled production of high amounts of soluble recombinant lectins.

Identification of three proteins involved in fertilization and parthenogenetic development of a brown alga, Scytosiphon lomentaria

Metabolic pathways of cell organelles may influence the expression of nuclear genes involved in fertilization and subsequent zygote development through a retrograde regulation. In Scytosiphon lomentaria, inheritance of chloroplast is biparental but mitochondria are maternally inherited. Male and female gametes underwent different parthenogenetic outcomes. Most (>99%) male gametes did not differentiate rhizoid cells or survived beyond four-cell stage, while over 95% of female gametes grew into mature asexual plants. Proteomic analysis showed that the protein contents of male and female gametes differed by approximately 1.7%, 12 sex-specific proteins out of 700 detected proteins. Three sex-specific proteins were isolated and identified using CAF-MALDI mass spectrometry and RACE-PCR. Among them, a male gamete-specific homoaconitate hydratase (HACN) and a female gamete-specific succinate semialdehyde dehydrogenase (SSADH) were predicted to be the genes involved in mitochondrial metabolic pathways. The expression level of both mitochondrial genes was dramatically changed at the fertilization event. During parthenogenetic development the male-specific HACN and GTP-binding protein were gradually down-regulated but SSADH stayed up-regulated up to 48h. To observe the effect of chemicals on the expression of these genes, male and female gametes were treated with γ-aminobutyric acid (GABA), hydrogen peroxide and L-ascorbic acid. Among them GABA treatment significantly reduced SSADH gene expression in female gamete but the same treatment induced high upregulation of the gene in male gamete. GABA treatment affected the behavior of gametes and their parthenogenetic development. Both gametes showed prolonged motile stage, retarded settlement and subsequent parthenogenetic development. Our results suggest that male and female gametes regulate mitochondrial metabolic pathways differentially during fertilization, which may be the reason for their physiological and behavioral differences.